STABILITY OF TERRESTRIAL ECOSYSTEMS AS TO PEST ORGANISMS: AN
AXIOMATIC APPROACH
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT
PESTS: AN AXIOMATIC APPROACH. PART II
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT
PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN
THE PART I
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18_Axiom8-1.doc
AXIOM 8(1) FACTORS of DISTURBANCE of ECOSYSTEM STABILITYto PLANT
PESTS and their EFFECTS
To keep ESPPs in any ecosystem on the admissible level as long
as possible, it should know the factors, which disturb it. A
meaning of the term "disturbance" needs in some sidelight. It
should pay attention on the difference between life strategy of
biocenoses and destination of articenoses.
The life strategy of biocenoses is directed on keeping ESPPs
biomass of the category D‑I on the level 3.1. "Proper control." The
decrease ESPPs in this category of biomass under diverse stressors
to the level 3.2. "Lag control" endangers biocenoses by a change of
composition of dominants. The decrease ESPPs of it on the level
3.3."Late control" results in destruction of biocenoses.
Contrary, on the biomass of the category D‑II, a decrease ESPPs
on the levels 3.2. and 3.3. has no a destructive character. In some
environmental conditions, it takes place an often decrease ESPPs to
the level 3.3. "Late control." The advanced Tolerance of dominants
allows biocenoses to survive in spite of the common affection by
herbivores. It is necessary, however, a periodic suppression of
herbivores by CESPPs 2.5. "Effects of crowding", which provides a
reprieve for restoring of vitality of dominants. Therefore, on
biomass of the category D‑I, a disturbance changes a character
of an ecosystem, and it is undesirable, whereas on biomass of the
category D‑II due to advanced Tolerance the term
a "disturbance" has no obligatory a negative sense.
The destination of articenoses, which is determined by people,
is directed on keeping the level ESPPs 3.1. "Proper control" both
in biomass of the categories D‑I and D‑II. When signs of a decrease
of ESPPs from the level ESPPs 3.1. "Proper control" appear, CESPPs
2.6. "Human control measures" usually need to be entered in an
operation. This is necessary in agricultural crops, where decrease
of yielding and keeping of quality of production are the main
concern of ecosystems. In ecosystems of other concern, the need of
application CESPPs 2.6. "Human control measures" depends on local
circumstances.
All the stressors, which decrease ESPPs from the level 3.1.
"Proper control", will be referred to as factors disturbing
ecosystem stability to plant pests (FDESPPs). Further, it will be
considered the conditions, at which diverse FDESPPs are active, and
their effects on dominants will be shown.
It has been declared the skepticism as to the durability
(persistence) of plant resistance to PPs, which is implied as
Antibiosis, due to arising of new pathotypes of phytopathogens and
new biotypes of herbivores, which would capable to overcome the
resistance.
Indeed, frequency of hereditary changes in PPs is much greater
than that in their host-plants. The microevolutionary process that
leads to a lost of the resistance in the system of interrelations "
a host-plant - a consumer" has been considered
by D. Pimental (1961 and other publications), and has got
the special term the "genetic feed-back mechanism." Beside the
mathematical proof, D. Pimental has given a number of
examples, which illustrate the action of this mechanism in nature.
It is known a row of cases, at which plant cultivars loss their
resistance to PPs in innumerous years after wide-scale growing of
these cultivars as field crops.
However, a lot of facts demonstrate the presence of an opposite
trend. In this connection, it should mention the words by
R.L. Gallun and G.S. Khush (1980, pp. 82‑83),
namely: "The breakdown of resistance may occur after few years
although in some cultivars resistance remains for the last
50 years."
Consider prospects of keeping of plant resistance to PPs taking
into account of FDESPPs and the circumstances, at which they are
active, as well as the ways to counteract losses of the
resistance.
8.1. Anthropic-1
8.1.1. Growing of cultivars in the range of exotic herbivores
r-strategists
Breakage of the prerequisites:
2.1.1.P.1. A hereditary ability of a plant taxon (species,
subspecies, phenological forms, varieties strains, hybrids, lines)
to resist against a given taxon of PPs
2.2.1.P.2. Adaptation of parasites and pathogens to overcome
resistance of their hosts
2.2.1.P.9. Presence of effective vectors of pathogens
8.1.1.1. CESPPs A.2.1.1.2.1. , 2.2.1., and 2.2.3. failed
8.1.1.1.1. Repeated arising of aggressive biotypes inducing
outbreaks of the herbivores
As examples of this category, it can be used the cases offered
by M.D. Pathak (1970). This is a list of pest insects,
including the Hessian fly, Mayetiola destructor and five species of
aphids, which overcome Antibiosis of their host-plants repeatedly
by producing aggressive biotypes. They are the raspberry aphid,
Amphoraphora rubi, the spotted alfalfa aphid, Theriophis maculata,
the greenbug, Schizaphis graminum, the corn leaf aphid,
Rhopalosiphum maidis, and the pea aphid, Acyrthosiphon pisum.
All the above species are r-strategists. The fly produces up to
five generations per season, whereas the aphids have to ten ones or
even more. The more number of generations of a herbivore per year,
the more hereditary changes in its population, the more probability
of arising of mutants with genes, which are able to overcome
host-plant Antibiosis, rather that Antibiosis in host-plants to the
above herbivores is not well-developed, if any.
These species feed on plant’s parts, which related to biomass of
the category D- II. In native lands of the herbivores, these
parts are protected by CESPPs A.2.1.1.3.1.2. "Tolerance to
herbivores, Repair or compensation of losses of host-plant tissues"
in cooperation with CESPPs 2.2.1. "Natural enemies of invertebrate
herbivores", A.2.1.2.1.1. "Superevasion from herbivores." or
2.1.1.4.1. "Evasion from herbivores." Being exotic species in North
America, they hardly to suffer seriously on the part of natural
enemies. At such circumstances, Tolerance is insufficient for
self-protection of host-plants. If breeding of varieties having
Antibiosis to the herbivores was conducted, the Antibiosis,
however, occurred to be not potent, when to take into account
specificity of tissues under the affection - young tillers,
juvenile parts of stems, and foliage. There are the grounds,
therefore, to consider the hereditary prerequisites of CESPPs
Antibiosis in the given case as failed ones. In literature, such
Antibiosis is characterized as monogenic one or the vertical
resistance.
A combination of the above factors: advanced capacity of the
herbivores - r-strategists to produce aggressive biotypes, low
activity, if any, of resident natural enemies of these exotic
herbivores, and weak expression of CESPPs A.2.1.1.2.1. "Antibiosis
to herbivores" in the crops results in the loss of Antibiosis.
Hereditary prerequisites of this Antibiosis in the above conditions
failed.
In this context, it should paid attention that in exotic
herbivores K-strategists, an arising of aggressive biotypes has not
been traced. This fact was reported again by M.D. Pathnak (1970),
in particular, in the wheat stem sawfly, Cephus cinctus and the
European corn borer, Ostrinia nubilalis. Further, the plant’s
parts, which are affected by these species, might by provided more
developed Antibiosis than that in the above herbivore
r-strategists. So that, hereditary prerequisites of CESPPs
A.2.1.1.2.1. "Antibiosis to herbivores" in the K-strategists are
rather durable ones.
Consider the ways to withstand an activity of FDESPPs 8.1.1.
"Growing of cultivars in the range of exotic herbivores
r-strategists." These ways are practicing of CESPPs A.2.1.2.1.1.
"Superevasion from herbivores", A.2.1.1.3.1.2. "Tolerance to
herbivores, Repair or compensation of losses of host-plant
tissues", and 2.2.1. "Natural enemies of invertebrate herbivores"
by means of introducing of them.
The Hessian fly is known in North America from XVIII century,
and it continues to be a serious pest mainly of the spring wheat
until now. It has been bred a number of cultivars with Antibiosis
to this pest, but duration of efficacy of this trait is limited due
to arising of aggressive biotypes of the pest. The author has not
found in literature reports about introducing of natural enemies of
the Hessian fly. Probably, such attempts were been conducted, but
they were not insistent.
The aggressiveness of the Hessian fly in America is more
expressed than that in Europe. That fact might be explained by
difference in activity of natural enemies of the Hessian fly in the
compared continents.
Considering of the well-documented situation with the Hessian
fly in Russia is able to bring clearness in the issue. This pest
probably invaded in this country in the middle of XIX century
or its aggressiveness was a result of mutation of a native species,
as A.F. Kryshtal (1950) supposed. Over nearly a century, it
was very dangerous, when its outbreaks arose with short
intervals.
The first outbreak was recorded in Russia in 1847. Since the
outbreaks were reported to be in 1879‑1885, 1890, 1896‑1898,
1906‑1908, 1911‑1913, 1923‑1925, 1937‑1938, 1948‑1955, 1961‑1963
(Pavlov, 1967, pp. 47‑48). The level of affection becomes
clear from the report by A.Ph. Kryshtal (1947, p. 12).
According to this scholar, in 1938, the fly's outbreak was the most
sever over 40‑50 preceding years. On 1,621,731 hectares
of the surveyed area in Ukraine, density of the fly (the number of
larvae or pupae per square meter of the soil surface) reached in
the spring wheat 300 individuals on 34.8% of the area and 1000
individuals on 8.6% of the area. In the winter wheat, the affection
with the rate over 300 individuals was on 12.8% of the crop's
area
Eventually, in USSR, the damage due to the Hessian fly has
become less. After 1960-ies, outbreaks of the Hessian fly were
recorded and forecasted in 1979‑1980, 1991‑1992 and in 2000‑2001
(Biletsky, 1994). However, any general increase of density of this
species in 1987‑2001 in Ukraine was not recorded
(G.A. Posylayeva, pers. comm. and author's observations). Over
last decades, in the Forest-Steppe biome in Ukraine, it is known
only one case of significant damage due to this species, namely: in
1972 several hectares of the winter wheat were damaged seriously by
the fly in a breeding center (L.A. Burdenyuk,
pers. comm.).
Even in the Steppe zone, where activity of the fly is usually
more expressed, it has not been recorded over 1990-ies the decrease
of grain yield in the winter wheat at the highest of the revealed
values of the density - affection of 46% of tillers in fall and
presence of cocoons in 14% in sheaths of stems in summer (Krut,
1992; 1998, pp. 51‑52).
In the past, aggressiveness of the Hessian fly in the Steppe
zone was higher. This problem was studied by P.I. Susidko
(1969), who reported the following terms of Hessian fly outbreaks
in the south of Ukraine (Ibid., pp. 19, 27): 1881, 1884‑1885,
1890, 1892, 1896‑1897, 1907‑1908, 1910‑1911, 1922‑1924, 1930‑1932,
1937‑1938, 1947‑1948, 1951‑1952, 1959, 1966. In 1959, on irrigated
wheat fields, the density of the Hessian fly exceeded
1000 larvae per square meter of the soil surface, so that one
affected stem contained in average more than three larvae
(Ibid.).
This species has developed SP – up to five generations per year
that allows it to give a quick rise of density.
P.I. Susidko (1969, p. 19) stressed that outbreaks of
the Hessian fly did not demonstrate any periodicity. Its High
density continued one-two years. Since then, it took place a
depression, which continued from one to ten years.
This view contradicts one keeping by Eu.S. Biletsky (1994),
who attempts to connect arising of Hessian fly outbreaks with the
periodicity of the solar activity.
As a cause of fluctuation of fly’s density, it might be
diversity of weather situations. The role of weather has been
stressed by A.F. Kryshtal (1972, pp. 504‑506). He has
noted that sharp change weather situation in spring from cold to
continual warm one promotes to growth of the density. Contrary, a
return of cold weather in spring after short warm weather induces
mortality of the neonate larvae. The stable wet weather during
summer does not promote an increase of the density, because the
flies are active, but they unable find host-plants in the
vulnerable stage – with young tillers, which are absent. On the
other hand, at droughty summer, the flies stay in diapause. In
fall, they become active and find abundant young tillers on winter
wheat fields. In addition, wet weather over summer promotes
activity of chalcidid parasites of the Hessian fly, whereas
droughty summer suppresses them (Rubtsov, 1938).
As an explanation of the trend to decrease of aggressiveness of
the Hessian fly, it can be proposed an adaptation of resident
natural enemies to use this species as a host. For substantiation
of this proposition, it can serve the data offered
by A.V. Znamensky (1926, p. 213). These data allow
comparing mortality of a fall generation of the Hessian fly in
Poltava (Ukraine) in 1923 at the early sowing date, and in
Lafayette, Ind. (USA). The observations in Lafayette were conducted
between September 11 and October 16, 1921. As to Poltava,
the data are obviously original ones by A.V. Znamensky. A
source of the data for Lafayette was not noted. In the
Table 38, it is shown the comparative mortality of a fall
generation of the Hessian fly in the stages of egg, larva, and
pupa.
Table 38. The comparative mortality of the Hessian fly in
Poltava (Ukraine) in 1923, and in Lafayette, Ind. (USA) in 1921
Location
Crop
The number of studied objects
Percentage of plantlets with eggs
Percentage of objects with larvae and pupae
The number of eggs per plantlet
The overall number of eggs
The overall number of larvae and pupae
Survivorship, percentage
Plantlets
Tillers
The number of tillers per plantlet
Plantlets
Tillers
1
2
3
4
5
6
7
8
9
10
11
12
Poltava
The winter wheat
212
1695
8
100
44
52
56
11872
28
0.23
The winter rye
189
1701
9
87
7
6
19
3116
7
0.22
Lafayette
The winter wheat
50
135
2.7
100
69
44
36
1796
284
15.8
The winter rye
50
410
8
90
6
0.7
12
580
7
1.3
The Table 38 demonstrates the great difference in survivorship
of the Hessian fly between the areas. In Lafayette, Ind. (USA), the
survivorship was much higher than that in Poltava (Ukraine). The
difference can be due to the better adaptation of natural enemies
(probably parasites and pathogens) to this insect host in Poltava
comparing with that in Lafayette.
Why does the activity of natural enemies of the Hessian fly in
Poltava is greater than that in Lafayette? The answer is the rich
fauna of relatives of the Hessian fly in Ukraine. In Europe,
including Ukraine, it was recorded a number of species of the genus
Mayetiola: M. avenae March., M. dactylidis Kieff.,
M. destructor Say, M. joannisi Kieff., M. schoberi
Barnes, and M. poae Bosc. (Mamayeva and Mamayev, 1981).
In Ukraine, on the Hessian fly, it has been recorded twenty
species of parasites (Bilanovs’ky, 1940, cited in
A.F. Kryshtal, 1974, p. 505). From them, the most
numerous are Eupteromalus micropterus, Merisus destructor,
Platigaster minutula, and Eupelmella vesicularis.
As an example of potency of the parasites, it can serve the wasp
Platygaster minutula Lind., Proctotrupidae, which oviposites in
eggs of the Hessian fly, and the progeny finishes development in
larvae or pupae; due to polyembriony, 15‑20 larvae of the parasite
develop from one of its egg (Shchegolev et al., 1949,
p. 389).
An activity of the parasites is high in vicinity of forest plots
and shelterbelts (Kryshtal, 1974, p. 505).
In wild vegetation, important role in SES is played by CESPPs
2.1.1.4.1. "Evasion from herbivores" operating on the level of
separate plants. In crops, it is very effective of CESPPs
A.2.1.2.1.1. "Superevasion from herbivores." Sowing of winter wheat
in the optimal dates, which have been determined for diversity of
States, prevents exposition of plants in vulnerable stage on the
flies (Fernald, 1926, p. 316).
The Superevasion is prospective concerning the spring wheat. In
fact, "In the spring-wheat section late seeding will not apply. It
seems likely, on the contrary, that the earlier it is sown in
spring the less it will suffer from the Hessian fly" (Fernald,
1926, p. 317).
The trait A.2.1.1.3.1.2. ''Tolerance to herbivores, Repair or
compensation of losses of host-plant tissues'' allows the crops to
survive in spite of significant activity of the Hessian fly.
Turning to the Table 38, it is noticable high general
tillering of the crops – eight tillers in the winter wheat and nine
tillers in the winter rye. Abundant tillering allows to plants to
tolerate losses of their tillers due to affection by the fly in
fall, and to restore tillers in spring. To overwinter succesfully,
a plant needs in only two tillers.
Nevertheless, CESPPs A.2.1.2.1.1. "Superevasion from herbivores"
is insufficient for reliable protection of the spring wheat and in
the winter wheat on condition that it grows in southern areas,
where the fly can be active over winter. In such a situation, it is
need cultivation of the varieties possessing the trait of expressed
Antibiosis to the Hessian fly.
The Antibiosis is prospective, particularly in North Kazakhstan.
Here, Mayetiola destructor is a tiresome pest (Yevdokimov et al.,
1986). In these climatic conditions, it is possible to grow only
the spring wheat, so that Superevasion is insufficient for the
protection. Arid climate does not promote abundant general
tillering, so that Tolerance is also insufficient. Further, areas
of natural woody ecosystems and shelterbelts, where pest's
parasites and predators find favorable conditions for overwintering
and additional (imaginal) feeding, are actually absent. At last,
here it is practiced the soil treatments without digging
up. In this area, it is necessary the surface tillage -
sharing for protection of the soil from wind erosion. That is why
the fly overwinters successfully into shready stalks, whereas the
wheat is grown as a monoculture.
At growing of wheat cultivars with Antibiosis to the Hessian
fly, recurrence of outbreaks takes place at arising of aggressive
biotypes of the pest. Contrary, growing of the winter wheat in the
conditions, where Superevasion is effective, Tolerance is
developed, and natural enemies of the fly are prosperous, results
in unlimited keeping of its density on the Insignificant level.
Population dynamics of the exotic species of aphids is similar
to that of the Hessian fly. This suggesion is concerned to the
above-cited species Amphoraphora rubi on the raspberry, Theriophis
maculata on the alfalfa, Schizaphis graminum on the wheat and the
sorgum, Rhopalosiphum maidis on the sorgum and the corn, and
Acyrthosiphon pisum on the pea, rather that Antibiosis against them
is not expressed well. In their EEs in the native land, the role of
Tolerance and activity of natural enemies is supposedly great one,
so that there is no need in developed Antibiosis. A cooperation of
all the above CESPPs provides admissible suppression of their
density. Contrary, in the recently invaded area, low activity of
natural enemies results in rather soon loss of Antibiosis. On the
other hand, Tolerance is insufficient for self-protection in the
conditions of high activity of herbivores – r-strategists.
Causes of outbreaks of the Russian wheat aphid, Diuraphis noxia
Mordv. (in the contemporary Russian literature, this species is
known as Brachycolus noxius Mordv.) can be included in this
category of FDESPPs. In Russia, this species was described at the
end of XIX century, when it occurred to be very abundant. In
fact, N.A. Kholodkovsky (1912, p. 488) reported that this
species (at that time, it was used the name the barley aphid,
Brachycolus korotnevi Mordv.) was appeared sometimes in huge masses
in south of Russia, and its imagoes composed vast clouds. Probably,
this species penetrated into this country shortly before the
outbreak. Eventually, density of this species has become Low
although breeding of resistance cultivars has not been
conducted.
Contemporary literature does not report about outbreaks of this
species in the areas of its former abundance in East Europe.
Diuraphis noxia is mentioned as a satellite of more important
pest - Sitobion avenae in south Ukraine (Nikolenko and Omel'chenko,
1974). In the Forest-Steppe zone, the role of the aphid is
considered as insignificant. In fact, the studies in 1976-1979
showed the presence of four species of aphids on the winter wheat,
including Diuraphis noxia, however, the occurrence of Sitobion
avenae equaled 92.4% (Dudnik, 1983, p. 6).
In East Germany, participation of Sitobion avenae in a total
aphid stock on the winter wheat was about 90% (Assman and Wetzel,
1990) that also suggested the minor role of Diuraphis
noxia.
It was reported that Diuraphis noxia is a species of the Central
Asia origin (Schliephake et al., 1998). It spreads westward
beginning with XIX century. The Low density of this species in
Europe in nowadays might be explained by adaptation of
resident natural enemies to suppress it.
FDESPPs 8.1.1. cooperates with FDESPPs 8.6.1. "Invasion of
exotic taxa of phytopathogens or herbivores, which are able to
overcome 2.1.1.2."
8.1. Anthropic-1
8.1.2. Growing of a single cultivar on vast areas
Breakage of the prerequisites:
2.1.1.P.1. A hereditary ability of a plant taxon (species,
subspecies, phenological forms, varieties strains, hybrids, lines)
to resist against a given taxon of PPs
8.1.2.1. CESPPs A.2.1.1.2.2. failed
8.1.2.1.1. Arising of high virulent pathotypes in resident
phytopathogens r-strategists inducing epiphytoties
The more an area of growing of a cultivar, the greater a
probability of a contact of its plants with virulent pathotypes
existing in nature, the more abundant agents of phytopathogens
contact with these plants, the greater a danger of arising of new
virulent pathotypes. That is why a trait of Antibiosis to
phytopathogens can be lost over innumerous years after beginning of
growing of a resistant cultivar on vast areas. This factor is of
big importance in the present time. Modern agriculture practiced in
developed countries is characterized by the growing of a few
cultivars of a crop on vast area. This is a general trend of the
progress, when the best cultivars quickly get recognition of
numerous growers.
Resistant cultivars growing on minute areas, for examples in
nurseries of breeding centers stay out of above threats. Here, a
trait of the resistance remains much longer than that in the
situation described above.
This FDESPPs is potent in phytopathogens r‑strategists such as
the rust and mildew species having numerous generations per year
and high mobility of their spores. As consequencies of r‑strategy,
it is great hereditary variability. Within a species of the
phytopathogens, there exist hundreds of pathotypes. In them, it
lacks the stage of saprophy, which are characteristic for
K‑strategists, in particular for the root rots. A lack of
saprophagy promotes a hereditary variability in a phytopathogen’s
population.
The selection with the trend of an increase of virulence leads
to extinction both of the pathotype and their host‑plants as well
as to defeat of a high‑virulent pathotype in competition with
pathotypes of less virulence. At this trend, the durability of
host-plant Antibiosis is low, but this is a blind alley in
microevolution of phytopathogens. This trend, which appears at
growing of a single cultivar on vast areas, directs of a
phytopathogen on the way of of high, but short-time virulence.
When growing a cultivar over vast areas, a loss of CESPPs
A.2.1.1.2.2. "Antibiosis to phytopathogens" is influenced by
diversity in virulence of subspecies taxa of a phytopathogen
depended on a locality. M.P. Lesovoy (1977, and subsequent
publications) stated that composition of races (and pathotypes)
within a species is diverse even on rather small distance. Thus, in
Ukraine, there are twenty Regions. M.P. Lesovoy and co-workers
reported that among these Regions, there are significant
differences, in particular as to virulence of pathotypes. The
occurrence of them (eigtheen pathotypes of the race 77 of the leaf
rust) on seven wild gremineous species in some localities is so
significant that growing in them of certain varieties of the winter
wheat is took the risk (Lesovoy, 1977, p. 24). Notably, that
presence of high virulent pathotypes does no preclude thriving of
wild plant species.
The diversity yielding of crops depending on a locality is known
long ago. In Soviet Union, it was organized a service of the Seed
Testing Stations – test plots, where newly bred varieties were
proved on diverse agronomic traits. In Ukraine, in every Region, it
has operated such a Station. The differences in yielding indeed
were recorded in spite of varieties were grown in favorable for a
given crop habitats, and differences in climatic conditions
sometimes were little. After advantages of a variety are proved, a
recommendation to grow a variety in a given Region is given.
It is accepted that at growing of a variety with monogenic
(vertical) resistance on vast areas, it will be overcome by
r-strategists during few years at least in some localities.
When FDESPPs 8.1.2. "Growing of a single cultivar on vast areas"
operates in a cooperation with FDESPPs 8.1.3. "Growing of cultivars
in the conditions of a lack of operation of CESPPs A.2.1.2.4.1."
loss of CESPPs A.2.1.1.2.2. "Antibiosis to phytopathogens" gets
more probable.
In phytopathogens K-strategists, the situation is different one.
The fact is the potato varieties resistant over many years to the
wart (cancer) disease, Synchytrium endobioticum Schild., whereas in
the case of the potato leaf blight, Phytophthora infestans (Ment.)
De Bary the trait of resistance is of short duration.
Yu.T. D’yakov (pers. comm.) explains these facts by different
strategies of these phytopathogens: the category "K" in the case of
the cancer, and "r" in the case of the blight.
8.1. Anthropic-1
8.1.3. Growing of cultivars in the conditions of a lack of
operation of CESPPs A.2.1.2.4.1.
Breakage of the prerequisites:
2.1.1.P.1. A hereditary ability of a plant taxon (species,
subspecies, phenological forms, varieties strains, hybrids, lines)
to resist against a given taxon of PPs
A.2.1.2.P.2. In articenoses, a resemblance of a dominant stock
to that in biocenoses or special cultural practices with the aim of
effective operation of CESPPs 2.1.2.
8.1.3.1. CESPPs A.2.1.1.2.2. failed
8.1.3.1.1. Arising of high virulent pathotypes in resident
phytopathogens r-strategists inducing epiphytoties
Host-plants select their phytopathogens on virulence. Only those
pathotypes of them survive, which are able either to co-exist with
host-plant Antibiosis or to overcome it. As to the latter, i.e. a
loss of Antibiosis, the successful pathotypes produce agents, whose
chance on survivorship is different depending on a character of a
stock of host-plants within an ecosystem. If the stock consists of
a single cultivar, its protective trait (Antibiosis) is the same in
all the plants. Therefore, there are no obstacles for a successful
pathotype to infest all the stock. Because the number of
generations per year in r‑strategists is numerous, an infection
spreads quickly over a stock. This capacity is called a high
aggressiveness of a pathotype.
Further, in this situation, it increases virulence of a
phytopathogen species due to an increase of participation of the
most virulent pathotype. This is so because in the conditions of an
unlimited spread of infection, it arises an intensive competition
among micelia. In the competition, it survives the micelia, which
have better possibility to suppress Antibiosis of host-plant, so
that they force out less virulent pathotypes. Therefore, at the
monotonous hereditary composition of a stock of host‑plants, it
gives rise new pathotypes with ever‑increasing virulence. This
trend, however, takes place on susceptible cultivars. Contrary, on
the cultivars with Tolerance, take place an opposite trend. Then,
less-virulent pahotypes force out high-virulent pathotypes.
From ancient times, humans have known consequences of the above
process. Therefore, they bred and used so called land races of
crops. Now, it is known that a land race is composed by a number of
hereditary very different entries, which, however, are identical in
their agronomical, phenological, and morphological traits.
This problem was considered above in this text at characteristic
of CESPPs of the category A.2.1.2.4.1. "Hereditary heterogeneity of
a stock of host-plants." In the same Section, it mentioned the ways
to counteract the process of increasing agressiveness and virulence
of phytopathogens. The ways consist in development of methods as to
increase of hereditary diversity in a stock of crops. In other
words, this is the concept of intrafield diversification, which
concerns growing of divers cultivars in mixture. In such
conditions, both virulence and aggressiveness of phytopathogens are
dumped; it survives the pathotypes, which are able to coexist with
their host-plants, so that Tolerance thrives.
In the case of operation of CESPPs 2.1.1.3.2. "Tolerance to
phytopathogens" and intrafield heterogeneity, the more virulent
pathotypes have no advantages comparing with less virulent ones.
Therefore, the above mentioned trend of forcing out of
high-virulent cultivars by less-vitulent ones becomes especially
expressed.
The FDESPPs 8.1.3. operates usually jointly with FDESPPs 8.1.2.
"Growing of a single cultivar on vast areas" that
redouble the negative effect of such cultural practices.
8.1. Anthropic-1
8.1.4. Growing of cultivars in the conditions unfavorable for
expression of
CESPPs A.2.1.1.2.
Breakage of the prerequisites:
2.1.1.P.1. A hereditary ability of a plant taxon (species,
subspecies, phenological forms, varieties strains, hybrids, lines)
to resist against a given taxon of PPs
2.3.P.2. Limitation of aggressiveness of PPs
8.1.4.1. CESPPs A.2.1.1.2.1. and A.2.1.1.2.2. failed
8.1.4.1.1. Affection by phytopatogens and herbivores
It was recorded a phenomenon, which considering by scholars as
an evidence of dependence of expression of Antibiosis genes on
ambient temperatures. The case stories were considered above at
characteristic of CESPPs 2.3. "Routine weather suppression."
In short words, affection of some wheat varieties by the Hessian
fly occurred to be equals 3% at 15°C and 97% at 27°C (Painter,
1958). The similar results were obtained in another study (Sosa and
Foster, 1976).
In phytopathogens, it was recorded a sudden loss of Antibiosis
to the leaf rust on the winter wheat at a sharp skip of the weather
situation from cold spring to hot summer (Gorlach, 1958,
p. 147). The loss took place two seasons. At other weather
situations, these varieties were resistant to the leaf rust over
many years.
At last, significant fluctuations of Antibiosis depending on
weather situation were recorded in species of the cabbage to
Plasmodiophora brassicae Wor. (Tyuterev, 1981).
These cases show that Antibiosis to PPs can be lost in some
seasons at specific weather situation or even continually if a
variety is grown in the climatic conditions, where destructive
weather situation is common.
8.1. Anthropic-1
8.1.5. Growing of cultivars in the conditions intensifying SP of
PPs
Breakage of the prerequisites:
2.1.1.P.1. A hereditary ability of a plant taxon (species,
subspecies, phenological forms, varieties strains, hybrids, lines)
to resist against a given taxon of PPs
2.3.P.2. Limitation of aggressiveness of PPs
2.4.P.1. Keeping of severity of the season of an year when
activity of PPs is suppressed
8.1.5.1. CESPPs A.2.1.1.2.1., A.2.1.1.2.2., and A.2.1.2.1.
failed
8.1.5.1.1. Affection by phytopathogens and herbivores
In tropical and subtropical climates, PPs are able do not stop
their development over entire year. Application of irrigation leads
to the same situation even if climate of an area includes a dry
season. The factor of a seasonal limitation does not operate, when
growing of agricultural crops in greenhouses independently to
climate of an area, if summer interval in growing does not
practiced. In such conditions, it increases both the number of
generations of PPs and velocity of completion of life cycle. In so
doing, an increase of populations becomes maximal.
Because CESPPs 2.4. "Periodic (bottle-neck) suppression" does
not operate, CESPPs A.2.1.2.1. "Superevasion" does not operate
also. Further, an amount of agents of phytopathogens becomes so
large that they can overcome even advanced Antibiosis.
The same might be true for herbivores, especially sap-sucking
ones. This is an increase of their aggressiveness.
A virulence of phytopathogens grows also. This is so because at
competition of overcrowded micelia, the most virulent mutants
obtain selective advantage. The stages of saprophagy and dormancy,
which retard selection on the best parasitism, are absent. This is
an additional factor of increase of virulence. Thus, CESPPs
A.2.1.1.2. "Antibiosis" is ineffective.
The above conditions are very valuable for estimation of CESPPs
A.2.1. "Plant resistance to PPs." If an entry occurs to be
resistant in such a severe pressing on the part PPs, its resistance
would be durable in less severe conditions.
8.1. Anthropic-1
8.1.6. Growing of cultivars with spontaneous decrease of CESPPs
A.2.1.1.2.2. especially at specific weather situations
Breakage of the prerequisites:
2.1.1.P.1. A hereditary ability of a plant taxon (species,
subspecies, phenological forms, varieties strains, hybrids, lines)
to resist against a given taxon of PPs
2.3.P.2. Limitation of aggressiveness of PPs
8.1.6.1. CESPPs A.2.1.1.2.2. failed
8.1.6.1.1. Affection by phytopathogens
This category of losses of CESPPs A.2.1.1.2.2. "Antibiosis to
phytopathogens" has not been described in literature yet.
Therefore, it deserves a consideration in detail, rather that the
counteraction to this FDESPPs seems to be prospective to bring
clearness in the principal issues of plant resistance to PPs.
The widely accepted concept assumes that plant resistance to PPs
is durable if it has the polygenic character, whereas a durability
of the monogenic resistance occurs is a rare event. However, it is
not easily to gain an understanding, which kind of character
(monogenic or polygenic) a resistance has in a concrete case.
To illustrate this statement, consider the case of a loss of
resistance of the winter wheat varieties Avrora and Kavkaz to the
leaf rust, Puccinia recondita Rob. ex Desm. f. sp. tritici
Erikss.
In the North Caucasus Area of Russia after 1960, the winter
wheat variety Bezostaya-1 got a wide spread ensuring highest grain
yield for that time – 4-5 metric tons per hectare in the best
environmental conditions. With the aim to shift this variety by
more productive ones, in 1968, it was bred the varieties Avrora and
Kavkaz, which produced 5-6 metric tons of grain per hectare.
High resistance to the leaf rust, which was a serious disease in
that region, was a valuable trait of these varieties.
M.P. Lisovyi (2001, p. 17) reported that "Any known in
that time race of the leaf rust did not affect them. The author of
these varieties Academician P.P. Luk’yanenko supposed that
their resistance to the phytopathogen would be not never lost."
The valuable traits of these varieties resulted in the rush
increase of areas of cultivation of them. In the North Caucasus and
Ukraine, the areas reached such values: in 1971 – 19,000 ha,
in 1972 – 337,000 ha, and in 1973 – 1,367,000 ha. In
1973, it came a crash. M.P. Lisovyi (2001, p. 18) wrote:
"The fact of a loss of the resistance by the varieties so affected
of health state of the breeder Academician P.P. Luk’yanenko
that he died due to a heart infarction on a field of the wheat got
brown in result of affection with the rust."
What is the cause of such sudden loss of the resistance?
M.P. Lisovyi (1977) supposed that the cause consisted in an
arising of new high virulent pathotypes of the race 77 of the
leaf rust. They were marked 16, 20, 22, 23, 25, 26, and 28.
Further, he considered this case as a didactic example of a failure
of the monogenic (vertical) resistance (Lisovyi, 2001,
p. 18).
But there exists a doubt as to validity of this statement. The
resistance was considered as monogenic one, despite these varieties
had been bred as resistant to all the races of the leaf rust as it
was noted above. Further, it is rather strange that new-arisen high
virulent pathotypes of the race 77 so quickly (during one
growing season) spread over the vast areas. It needs an additional
information to explain the above questions.
First of all, the studies in the North Caucasus in 1973 at the
epiphytoty of the leaf rust did not find out any new high virulent
pathotypes of the race 77 (Rudnev et al., 1975). The main pathotype
that induced this epiphytoty was the well-known 103 of the
race 77. Further, this pathotype affected not only the
varieties Avrora and Kavkaz, but all the varieties grown in this
region, including Bezostaya‑1, as well as the wild gramineous
species – Agropyrum dereshrum Fisch., Aegilops sp., Bromus
squarrosus L., B. arvensis L. ,and B. scoparius L. As to the wild
species, it is difficult to suppose that they also have the
monogenic type of the resistance.
The report by E.D. Rudnev et al (1975) suggests an impact
of the factor unconnected with the increase of virulence of the
phytopathogen, which has induced this general epiphytoty of
cereals. As to the case of Avrora and Kavkaz, another line of
reports indicates on operation of inapparent processes in heredity
of these varieties.
In 1969‑1970, resistance of these varieties to the leaf rust was
studied by means of artificial inoculation by diverse pathotypes of
the leaf rust (Shopina et al., 1972; Krayeva and Alekseyeva, 1972).
These studies showed that most part of plants in Avrora and Kavkaz
were resistant to all the rust pathotypes, but a few plants were
susceptible to the race 143; some plants were susceptible to the
races 77 and 122. In addition, the percentage of susceptible plants
depended on a provenance of seeds ("lines" according to these
scholars’ words). Those from the L’vov Region (Ukraine) were
affected by the leaf rust on the level 60-80% –much more than the
plants from seeds grown in other Regions.
The similar results were obtained in studies in Ukraine also
before the epiphytoty (Lesovoy and Fyodorova, 1974). In that time,
nearly 95% of plants within Avrora and Kavkaz were resistant to all
the pathotypes of the leaf rust, whereas the rest were susceptible
to a number pathotypes including the wide-spread races 21, 57, 77,
92, 130, 149, as well as the new, but unidentifined races marked
X1, X3, X8, X9. The proportion of the unindentified races was only
2-8% in various experiments.
Further, the studies by V.F. Peressypkin et al. (1975) revealed
a decrease of resistance of Avrora and Kavkaz over several years in
succession, and an influence of ecological conditions on the rate
of the resistance loss.
What is the factor, which has caused this epiphytoty? In
literature, there is a legible answer to this question. Here are
the words by P.S. Udintsov (1974, p. 39): "In last year
(in 1973), in the period of vegetation in North Caucasus, in the
Regions of the Center (the Forest‑Steppe), the Central Chernozem
Area, and the Volga River Basin, in many Regions of Ukraine, it
occurred to be very favorable weather conditions for activity of
the leaf rust on the wheat. The widest spread of this disease was
recorded in the Krasnodar Region. Here, in the preceding fall, it
was accumulated a great many infection on voluntary wheat. After a
good overwintering and exclusively favorable conditions for the
phytopathogen in spring and summer, it arose an epiphytoty of the
disease. In some fields, the wheat varieties Avrora and Kavkaz,
which formerly were considered as resistant to this phytopathogen,
were affected on 80‑95% especially on areas with early sowing dates
and a high rate of fertilization by nitrogen comparing with the
rate of fertilization by phosphorus and potassium."
E.D. Rudnev et al. (1975) also supposed that the epiphytoty
was provoked by weather conditions favorable for activity of the
leaf rust, rather than by arising of a high virulent pathotype.
The provocative role of weather situation favorable for the leaf
rust was noted in the previous literature. Here is the report by
M.V. Gorlenko (1973, p. 217): "According to the data by
A.A. Gorlach (1954), a sharp change of outer conditions led to
weakening and subsequent loss of wheat resistance to the leaf rust.
In 1951 and 1953, in the Belaya Tserkov District (Ukrainian SSR)
after prolonged cool in spring, it came suddenly hot weather. This
led to serious affection of resistant varieties of the wheat by the
leaf rust. Bad overwintering also can increase susceptibility of
resistant varieties. Therefore, to be resistant to the leaf rust,
varieties need to be provided by traits of winter-hardness and
drought-hardness."
In The V.M. Remeslo Myronivka Institute of Wheat, in 1999
it was observed the mass affection by the leaf rust of all the
wheat entries with the exception of the variety Kryzhynka. Here, in
2001 at uncommonly wet weather in spring and summer, nearly all the
entries were affected by the root rots and the saprophagous fungi
on spikes. The only exception was the variety Remeslivna.
Nevertheless, in above cases, a decrease of the resistance took
place only over a season with the peculiar weather situation. On
the other hand, the epiphytoty of 1973 showed the continual fail of
the resistance in the Avrora and Kavkar. In a result, these
varieties disappeared from grower’s fields.
An irrigation of wheat fields practiced in areas of arid (warm)
climate enhances affection of the wheat with the leaf rust, so that
a decrease of grain yield reaches 4‑5% (Chumakov, 1963, cited in
J. Lilley, 1976). This finding might be explained by setting
up optimal conditions for vital activity of the leaf rust at
combination of high humidity of air and favorable ambient
temperatures. These data suggest heavy affection by the leaf rust,
because irrigation increases grain yield if it does not accompanied
by disease. This is another example of greater importance of
weather situation than hereditary grounds of resistance to a
phytopathogen.
The similarity of such effects might be seen at considering the
data of laboratory studies, where the resistance was evaluated at
optimum for vital activity of phytopathogen agents. In fact, the
varieties of winter wheat Myronivs’ka‑33 and Myronivs’ka‑34 were
nearly immune to the leaf rust at evaluating in conventional
breeding nurseries. However, when they were evaluated being
inoculated by this phytopathogen in the laboratory conditions, a
significant part of their plants (32‑67%) was susceptible or had
low resistance (Rudenko, 1997).
In the environmental conditions favorable for a given
phytopathogen species, it grows infectious loading by its agents
and their vitality, i.e. its aggressiveness. This brings danger for
any its host-plant. In addition, these conditions are able to
decrease protective response of host-plants, because for expression
of resistance trait, it needs staying of environmental factors in
some range.
In fact, there are the data about the important role of air
temperature for expression of resistance in the wheat against the
stem rust. N.H. Luig and S. Rajaram (1972) showed that
genes of resistance to the stem rust, Puccinia graminis Pers. f.
tritici Erikss et Henn. are inactivated at temperatures 27‑30°C.
The same might be true for the resistance to the leaf rust in the
varieties Avrora and Kavkaz. High percentage of susceptible plants
in populations of them from the L’vov Region according to
G.A. Krayeva and T.P. Alekseyeva (1972) suggests validity
of this idea. The climate of the L’vov Region differs significantly
from the above-mentioned territories (the Kiev Region, and
especially the Krasnodar Region). This resistance can be fixed in
heredity of the varieties being temperature-depended or
moisture-depended.
Turning to the question of the character of rust resistance in
the varieties Avrora and Kavkaz, it should note that the
supposition as to the monogenic type is based on the only
experiment. In the experiment, it was obtained F1B1 of the first
backcross with Avrora and Kavkaz as donors of the resistance, and
the variety Mironovskaya-808 as a recipient. In this generation,
the number of plants resistant and susceptible to the race 77
corresponded the ratio 1:1 at rather low index of validity (P) –
0.95+/-0.25 (Lesovoy, 1977, p. 40).
The conclusion from this experiment that the resistance of
Avrora and Kavkaz has a monogenic character is dubious, rather that
exactly M.P. Lisovyi (2001, p. 17), has spoken the words:
"Any known in that time race of the leaf rust did not affect them."
This is charateristic just for polygenic resistance.
How do to explain above data from concepts of genetics? It has
been known the patterns of gene activity within a taxon, which was
defined by N.V. Timofeyeff-Ressovsky as the penentrance and
the expressiveness of a gene (cited in M.E. Lobashov, 1967,
pp. 567‑568). The penentrance is determined by percentage of
organisms with a certain trait, when the organisms stay in the same
conditions. This index shows a uniformity of a taxon’s population.
The expressiveness is determined by percentage of organisms with a
certain trait, when they stay in diverse conditions. Thus, the
latter shows the response of a gene on factors of the
environment.
The varieties Avrora and Kavkaz had the high penentrance of gene
resistance to the leaf rust in the conditions far from optimum for
this phytopathogen, but their expressiveness occurred to be low,
when the conditions become optimal. In subsequent years, this
defect took place at any conditions, i.e. the trait of the high
penentrance can be lost entirely.
The capacity of the variety Bezostaya-1 to produce good yielding
in the conditions favorable for aggressiveness of the leaf rust
implies advanced expressiveness of this variety.
In the field evaluation of resistance of wheat varieties to the
leaf rust, the Myronivs’ka‑33 and Myronivs’ka‑34 had high
penentrance in the non-optimal conditions to the rust, and the low
indices of expessiveness in the optimal for the rust conditions in
a laboratory.
Above consideration allows drawing some conclusions as to causes
of loss of resistance on the example of well-studies interrelations
– the wheat and the leaf rust as follows:
i) The speculations as to resistance to the leaf rust is
determined exceptionally by the number of relevant genes are not
convincing.
ii) There exist the factors, which induce a progressive decrease
of the resistance in successive generations with participation of
destructive effect of some weather factors.
iii) The loss of resistance might be induced by an operation of
FDESPPs 8.1.6. "Growing of cultivars with spontaneous decrease of
CESPPs A.2.1.1.2.2. especially at specific weather situations."
iv) The loss of resistance might be induced by an operation of
FDESPPs 8.1.4. "Growing of cultivars in the conditions unfavorable
for expression of CESPPs A.2.1.1.2."
v) It might be the effect of FDESPPs 8.1.6. in successive
generations proceeds as follows. The plants within a stem stock
compete with each other. In so doing, they undergo natural
selection on the part of diverse stressors (capacity to utilize
resources, to withstand frost, resistance to other phytopathogens,
etc.). Plants with the better capacity can have advantages
comparing with plants having resistance to the leaf rust.
Percentage of the latter decreases, i.e. penentrance of the gene of
resistance in successive generations becomes lower.
DISCUSSION
The data on FDESPPs of the category 8.1. "Anthropic (hereditary
imperfection of cultivars at certain circumstances") inspire to
consider the issue of durability of plant resistance to PPs in the
context of microevolutionary processes in the system "a host-plant
– a consumer." In so doing, it will be used the data for both in
agricultural crops and wild species, as to phytopathogens and
herbivores.
The epiphytoty of 1973 allows understanding a sense of plant
resistance to phytopathogens in crops. The sense consists in a
holding of grain yield, rather than in low values of affection
indices. This becomes clear, when comparing the yielding and
affection of various wheat varieties.
In 1973 in North Caucasus, the losses of grain yield were the
following: Avrora – 20%, Kavkaz – 16%, Bezostaya‑1 – 9%
(A.A. Morozova, 1974, cited in N.M. Stepanov et al.,
1976). The less loss in Bezostaya-1 is of a special interest. The
matter of fact that before the epiphytoty, this variety was known
as susceptible to the leaf rust in contrast to the resistant Avrora
and Kavkaz. All the plants of Bezostaya‑1 were susceptible to most
of pathotypes of the leaf rust (Krayeva and Alekseyeva, 1972).
In the the study by A.M. Dymchenko et al. (1990), it was
evaluated of resistance of sixty-seven wheat varieties at heavy
doses of inoculum by eight pathotypes of the leaf rust. In it,
Bezostaya-1 occurred to be the first as to rate of affection
(75‑100% of a leaf surface) and the least as to yield loss –
0.6‑0.8 metric tons per hectare.
The capacity of Bezostaya‑1 to maintain high grain yielding at
heavy loading of pathogen’s agents is a good example of supremacy
of CESPPs A.2.1.1.3.2."Tolerance to phytopathogens" comparing with
CESPPs A.2.1.1.2.2. "Antibiosis to phytopathogens" as a means of
self-protection.
The data of studies cited above show that an inoculation by
actually all the pathotypes including those known as high virulent
on Bezostaya‑1 occurs to be successful. Hence, this variety is able
to enter in compatible interrelations with every of them. According
to the classification of the present report, this is CESPPs
A.2.1.1.3.2.2.1. "Tolerance to phytopathogens, Symbiosis with
former parasites, Compatibility."
The gene sources, which determine such traits of Bezostaya-1 are
shown by M.E. Lobashov (1967, pp. 639‑640). In this book,
it is presented the pedigree of this variety. Among its ancestors,
there are twenty-one varieties including well-known foreign and
resident ones close to land races. The former includes Squarehead,
Spyk, Lancaster, Fulz, Klein‑33, Kanred, Rieti and others. The
resident varieties are presented by Ukrainka, Krymka, Yefimovka,
Mestnaya (this Russian word means "local"). One of the nearest
ancestors is the variety Skorospelka-2. (this Russian word means an
"early matured crop"). This implies that Bezostaya‑1 has one more
trait – CESPPs A.2.1.2.1.2. "Superevasion from phytopathogens."
In subsequent years, to replace Bezostaya‑1, it has been growing
the more productive varieties with significant A.2.1.1.3.2.
"Tolerance to phytopathogens" to the leaf rust. One of them, it was
the variety Myronivs’ka‑61, which having a moderate numeric score
of the resistance - 5 (the maximal score in the scale is 9), had
been a leader in Ukraine as to grain yielding over 10 years
until 2000.
In 1990, this variety was aworded with the Golden medal in
All-Union Exhibition of Achievements of Soviet Economics in Moscow.
Such an awordment occurred to be the last in history. In 1991,
Soviet Union underwent a collaps.
Yu.T. D’yakov (1985, p. 168) has reported that the
Tolerance is accepted as most prospective factor of resistance of
the wheat and the oat against the mildew, Erysiphe graminis D.C.,
f. tritici March. At breeding on the resistance, it is practiced to
cull both heavy affected plants and immune ones, whereas plants
with the moderate level of the affection are selected. The mildew
has exclusive capacity to produce new pathotypes, so that its
capacity to overcome Antibiosis is well developed. The immune
plants have less productivity than those with the moderate level of
affection, because the former spend more resources for
self-protection.
The heredity of wild plant species has not been changed by
breeding. Therefore, it should suppose that the hereditary base of
their resistance to phytopathogens is quite potent. That is why, it
is interesting to consider these interrelations. The study have
been conducted by M.P. Lesovoy (1977, p. 24) on seven
species of wild cereal species showed that they year after year
have signs of affection by eighteen biotypes of the 77 race of
the leaf rust. The wild species are considered by this scholar as a
source of high virulent infection for cultivated cereals, and as a
cause of significant losses of grain yield.
The effect of the leaf rust on productivity or vitality of wild
species has not been studied. But simple speculations suggest that
the negative effect is negligible, if any. Otherwise, vitality of
plants in these species would be suppressed, and they would be
replaced by healthy competitors. Thus, the considered
interrelations are concerned to the Tolerance. Most probably this
is CESPPs 2.1.1.3.2.2.1. "Tolerance to phytopathogens, Symbiosis
with former parasites, Compatibility" or CESPPs 2.1.1.2.3.2.2.2.
"Tolerance to phytopathogens, Symbiosis with former parasites,
Mutualism."
The durability of the CESPPs 2.1.1.3.2. "Tolerance to
phytopathogens" has the theoretical grounds. In this case,
microevolution of phytopathogens is directed on success in
competition with pathotypes, which co-exist with their host-plants,
rather than on growth of virulence. This fact has been noted by
J.F. Schafer (1971, p. 248) in the following words: "The
lack of selective pressure on the pathogen, making tolerance more
stable than true resistance (M.D. Simons) is the one big
advantage of tolerance over resistance which provides equal
protection."
Further, low virulent pathotypes at an operation of Tolerance
protect their host-plants from high virulent ones gaining a victory
in competition, when infesting of host-plants.
In this context, it should quote D.R. Marshal (1977,
p. 10): "…there is a strong negative correlation between the
number of genes for virulence carried by a pathogen biotype and its
fitness, it is by no means universally true."
Thus, the potent hereditary base of plants resistance in wild
grassy plants to phytopathogens – r‑strategists consists in
operation CESPPs 2.1.1.3.2. "Tolerance to phytopathogens", and
2.1.1.4.2. "Evasion from phytopathogens." When cultivars have such
traits, they are close in their self-protection to wild species
that do not decrease agronomic traits of the former.
There is the trend to consider the resistance to phytopathogens
as Antibiosis, i.e. to record signs of the affection, and do not
notice the traits of Tolerance and Evasion, which manifest
themseves by capacity to keep productivity in time and space. For
example, M.P. Lisovyi (2001, pp. 22‑23) characterizes the
variety Mironovskaya-808 as having no significant resistance to the
leaf rust, because numeric score of affection by this phytopathogen
is rather low. This variety, however, might be considered as having
advanced Tolerance to the leaf rust, because it keeps productivity
over a number of decades in diverse environmental conditions.
V.V. Shelepov et al. (2004, p. 432) characterize the variety
Myronovs’ka 61 and Myronovs’ka 65 as ones, which “are affected by
the diseases in medium level” (to the leaf rust and the mildue),
although their grain yield is highest within a list of the shown
varieties – 10. 24 and 10.30 metric tons per hectare
correspondently. This is a case, when Tolerance is concidered as
signs of affection. To the point, both the varieties were bred by
V.V. Shelepov.
Wild woody plants also have their heredity untouched by humans.
The prerequisite of their resistance to PPs 2.2.2.P.1. "A
hereditary ability of a plant taxa (species, subspecies,
phenological forms, varieties strains, hybrids, lines) to resist
against a given taxon of PPs" is supposed to be proper. It is
relevant to compare means of maintenance of their resistance to PPs
with those in grassy plants.
In wild woody plants, the durability of resistance to
phytopathogens is obviously the same as that in grassy species. In
trees, it is known the cases of increase of damage on the part of
resident species, and the cases of catastrophic mortality of trees
on vast areas up to extinction. The causes of the mass mortality
consist in penetrating into the range of a tree species the
phytopathogens, which have not been factors of natural selection
for this species. The same take place at growing of a tree species
in an areas isolated from its natural range, where it is attacked
by resident phytopathogens. The latter, again, have not been a
factor of the selection.
The examples of such events are well known. The epiphytoties
induced by species-invaders are those of the Dutch elm disease,
Cerastocystis ulmi (Buismen) C. Moreau, the East American
chestnut disease, Endotia parasitica (Murr.) A & A, and the
European stem rust, Cronartium ribicola Diet.
Heavy epiphytoties in trees grown outside of their natural range
in isolated areas are known for the rust fungus on the coffee tree
in Ceylon, West Africa and Brazil, the virus disease on the
cocoa-tree in Africa.
In nature, there exist, however, the obstacles to extinction
under impact of the high virulent phytopathogens. First of all,
this is CESPPs 2.1.2.4.1. "Hereditary heterogeneity of a stock of
host-plants." The second obstacle is CESPPs 2.2.3. "Natural enemies
of phytopathogens." They suppress virulence of phytopathogens, so
that the diseases induced by them get a chronic character, rather
than acute one.
Consider some facts, which might be supposed as an impact of
indeed natural enemies of phytopathogens. The discourse is given
according to Yu.T. D’yakov (1985, pp. 58‑62 and 205‑209).
The Dutch elm disease appeared in Europe in 1918, and over the
period more that 30 years killed millions of elm trees. In
1950‑ies, its virulence began to decrease. Newly affected trees
ceased to appear, and formerly effected trees recovered. It seemed
that the disease became similar to resident phytopathogens, which
affected exclusively weakened trees. However, in 1967, it began the
second epiphytoty of the disease the same as severe as the first
one. The studies showed that this epiphytoty was caused by a new
pathotype penetrated from Canada, whereas the first epiphytoty was
induced by a pathotype penetrated from China.
What is the cause of the decrease of virulence in the first
epiphytoty? The answer has not been found by the author in
literature. Nevertheless, the explanation of this phenomenon might
be inspired by studies of other diseases. The case is the East
American chestnut disease. In these studies, it was found out
pathotypes of the phytopathogen of low virulence. When they were
inoculated on trees affected by common pathotypes, i.e. of high
virulence, these trees began to recover. Further studies showed
that the pathotypes of low virulence contained own parasites –
virus-like particles, and the recovering of affected trees was a
result of a spread of the virus-like infection on a micelium of the
high virulent pathotype.
It is logical to suppose that if a hyperparasite appears in a
population of phytopathogen, and spread within it, this leads to a
decrease of its virulence. This is a hypothetical cause of the
decrease of virulence at the first epiphytoty of the Dutch elm
disease. The next step is to spread this hypothesis on other
invading taxa of phytopathogens.
The chain composed by a phytopathogen (a rust fungus), its
parasite (a bacterium) and hyperparasite (a bacteriophage) is known
on the wheat and other cereal species (Klement and Kiraly,
1957).
G.E. Russel (1978) has paid attention on the fact that
actually all the cases of losses of resistance to phytopathogens
are concerned situation, when operate physiological (biochemical)
mechanisms of this trait (in the present report, this is the CESPPs
A.2.1.1.2.2.2.1.) Such a category of plant self-defense occurred to
be less durable than other ones.
Contrary, the structural Antibiosis (in the present report, this
is CESPPs A.2.1.1.2.2.1.1.) operates over unlimited time. Probably,
the self-protection is especially durable if it consists of a
combination of external structures and toxic factors. The
protective means of such a principle has been developed by humans.
This is the Beaurdeaux mixture consisting of solutions of cupric
vitiriol and lime. It uses for spraying of plants before
phytopathogen's agents come on plant surface. This preparation has
been used over more one hundred years, but the resistance to it in
phytopathogens has not been found out yet (Robinson, 1980). As to
contemporary systemic fungicides, they become ineffective in not so
many years after beginning of usage of them in a wide-scale due to
acquired resistance of phytopathogens to the fungicides.
In a breeding process for selection the entries having the most
expressed resistance to PPs, it has been used the method of
evaluation of this trait in the conditions optimal for an
affection. For example, it is practiced growing of wheat entries in
areas of tropical climate optimal for activity of the rust
phytopathogens. This allows selection of entries with the less
affection. Naturally, they have the most potent hereditary base of
resistance to these phytopathogens. These are the grounds to
suppose that their resistance to them would be durable in less
severe environmental conditions. Screening of crop’s entries on PPs
resistance in the plots with increased loading by these organisms
is bases on the same principle. These measures use the FDESPPs
8.1.5. "Growing of cultivars in the conditions enhancing of SP of
PPs."
As to insect herbivores, the theoretical substantiation of
durability of Tolerance also has been done. E. Horber (1974) has
supposed that the Tolerance cannot be overcome by herbivores at
all. This is so because the plants with this trait are not
undergone selective pressure on the part of herbivores. The
Tolerance neither kills herbivores, nor suppresses vitality of
them. It allows to herbivores to reach significant density. In
turn, it provokes an activity of their natural enemies, which
suppress the hervivore hosts.
Insect defoliators and sap-sucking arthropods are exposed to
suppressive effect of weather factors – CESPPs 2.3."Routine weather
suppression." Therefore, the evolutionary evolving of herbivores in
the case of operation of CESPPs 2.1.1.3.1."Tolerance to herbivores"
moves in the direction to counteract these factors of mortality,
and to decrease the negative effect on their host-plants. Further,
presence of herbivores on plants in Moderate density exert even
beneficial effect of these plants by means of enrichment of the
soil. The sources of such enrichment are excrements of these
herbivores and their predators, especially birds, and bodies of
died herbivores. Honey dew of aphids enhances greatly activity of
nitrogen-fixing organisms in the soil.
The durability of CESPPs A.2.1.2.1.1."Superevasion from
herbivores" is based on the fact that vital activity of plants is
possible at lower temperatures than that in arthropod herbivores.
Moreover, they strengthen A.2.1.2.1.1. "Superevasion from
herbivores" by culling the host-plants with less expression of this
trait.
In this context, it should cite I.E. Pavlov (1967,
pp. 170‑171), who has reported that many varieties of the
barley (Nutans-187, Europeum, Winner, Nossovsky, and others) have
been bred many years ago. Nevertheless, their resistance to the
flies Oscinella frit L. and O. pusilla Mg. not only remains until
now, but even it is increasing. These varieties grow quickly in
spring, so that before the beginning of the flight period of the
flies, their tillers become hardened. Therefore, the flies’ larvae
cannot feed in them. Thus, the flies exert selection of most
fast-growing plants of the barley.
The Hessian fly, Mayetiola destructor is an interesting case of
sudden appearing as a pest, probably being a native species in the
range of its heavy damage in Russia. A.F. Kryshtal (1950) showed
that close relatives of the Hessian fly feed on cereal species in
humid habitats, whereas the fly feeds mainly in mesophytic habitats
on various varieties and species of the wheat, Triticum spp., the
rye, Secale spp., the barley, Hordeum spp. and on the
couch-grass, Agropyrum spp., in particular Agropyrum repens (L.)
P.B.
The change of habitats by the fly and growing of host-plants
favorable for ancestors of the fly has been accompanied by forming
of species traits and capacity to inflict heavy damage. A.F.
Kryshtal (1950) supposes that the family Itonididae (Cecidomyiidae)
in the present time is in a stage of abundant species forming.
Consider the issue: what is the cause of differencies in
interelations of the Hessian fly with field crops, on the one hand,
and the fly with the couch-grasses, on the other hand? In the
European part of Russia, the Hessian fly was serious pest of cereal
crops (mainly the wheat) over nearly a century. The couch-grasses
are common host-plants for the fly. The couch-grasses are
wide-spread and tiresome long-standing weeds. The question is why
does being favorite host-plants of the fly, the couch-grasses have
not been undergone a depression?
This fact implies that the couch-grasses has effective
resistance probably of the categories of CESPPs 2.1.1.3.1.2.
"Tolerance to herbivores, Repair or compensation of losses of
host-plant tissues" and/or 2.1.1.3.1.3. "Tolerance to herbivores,
indifference to losses of host-plant tissues." The group of
couch-grasses has the trait to store abundant resources in their
root systems that allow it to produce seeds in spite of affection
of some part of tillers, and to restore their tillers, when
affection by grazing and insects colonization. In addition, it is
probable the significant role of 2.1.1.4.1. "Evasion from
herbivores."
In cereal cultivars, the traits serving as the above CESPPs are
expressed less. Therefore, Mayetiola destructor endangers them more
than the couch-grasses.
As an example of longevity of CESPPs A.2.1.2.1.1. "Superevasion
from herbivores", it can serve the usage in North America until now
the optimal (late) sowing dates of the winter wheat for protection
against the Hessian fly. This measure is practiced over a hundred
of years, but still is effective.
In woody plants, the CESPPs 2.1.1.2.1.2.1."Antibiosis to
herbivores, Physiological (biochemical), Permanent" is quite
durable. Long co-evolution of woody plants with their PPs has led
to development of exclusively multilateral traits of
self-protection of assimilative tissues in coniferous species and
vascular tissues in all the woody species. The protective product
of coniferous species – oleoresin consists of up to fifty toxic for
PPs substances. Also eucalyptes are protected by great diversity of
adequate substances. In volatiles of their foliage, it has been
found out about 270 organic compounds probably of a protective
concern (D’yakov, 1985, pp. 79‑80).
Nevertheless, it is necessary for self-protection of coniferous
tree species something more than only the presence of toxic
substances in tissues. In fact, in tissues of weakened trees, the
content of oleoresin is the same as that in healthy ones. This does
not provide an obstacle for numerous species consuming coniferous
species. The difference between healthy and weakened coniferous
trees consists in a capacity of the former to convey oleoresin to
attacking herbivores or to wounds that protects them against
phytopathogens. In a result, attacking PPs occur inside a toxic and
viscous product, whose amount is much greater than a mass of
herbivore bodies or agents of phytopathogens. On the air, oleoresin
becomes solid. Under such a complex effect, even rather large
beetles die. Killing of bark beetles in oleoresin on a stem surface
(in pitch tubes) or in bark of their host-trees is a common event.
The same takes place at attacks of healthy treea by other stem
borers, For example, A.S. Rozhkov (1982) reported about mortality
in exuding oleoresin up to 70% larvae of the longhorned beetle,
Xylotrechus altaicus Gebl.
The great variety of protective substances in coniferous and
eucalyptes species suggests that their resistance has indeed
polygenic character. This is the case of the factor durability.
An additional obstacle for surviving of PPs in coniferous
species consists in diversity of composition of turpentine within a
species. Among samples of turpentine taken in trees a plot, there
are no the trees having the same composition. Therefore, in such
ecosystems, it operates CESPPs 2.1.2.4.1. "Hereditary heterogeneity
of a stock of host-plants."
The complicated composition and peculiar physical properties of
oleoresin hamper to consume this product. It is free of consumers
with the exception of the little group of insects, which are called
"resinocols" (Mamayev, 1971). They need to pay for feeding such an
uncommon foodstuff by slow development and high mortality that
result in Low density.
The ecosystems of coniferous tree species, where conductive and
assimilative tissues concerned the biomass D‑I, they are propected
from PPs by CESPPs 2.1.1.2. "Antibiosis."
In woody deciduous tree species, CESPPs 2.1.1.2. "Antibiosis"
operates only in conductive tissues. This is the biomass of the
category D‑I. In the biomass D‑II of these species, it operates
CESPPs 2.1.1.3."Tolerance" and being in a cooperation with CESPPs
2.2."Natural enemies", 2.3."Routine weather suppression", and 2.4.
"Periodic (bottle-neck) suppression." These CESPPs provide
durability of ESPPs on the level 3.1. "Proper control" that is
demonstrated by flourishing of these ecosystems, if they have not
been disturbed by humans or natural force-majeur impacts.
As to the defoliators, which inflict insignificant damage for
host-trees, it is tolerable a decrease ESPPs to the level 3.2. "Lag
control" by CESPPs 2.1.2.1. "Superevasion" or 2.1.1.4. "Evasion" in
a cooperation with other CESPPs, so that these categories of
host-plant to PPs also provide ESPPs with durability.
The hereditary prerequisite of all the subcategories of the in
wild woody plant species retains in all the circumstances, except
the cases of invasion of species-strangers and growing of tree
species outside of their natural range.
To summing up. The durability of ESPPs is provided by
diverse CESPPs on condition that their hereditary prerequisite is
proper. Depending on the category of biomass, these CESPPs are the
following:
vi) On biomass of the category D‑II (assimilative tissues,
tillers), CESPPs 2.1.1.3. (A.2.1.1.3.) "Tolerance" (diverse
subcategories) and CESPPs 2.1.2.1. (A.2.1.2.1.) "Superevasion" or
2.1.1.4. "Evasion."
vii) On biomass of the category D‑I (vascular tissues,
assimilative tissues in evergreen coniferous species and in the
eucalyptes), 2.1.1.2. "Antibiosis", and 2.1.1.1.
"Nonpreference."
These points correspond to understanding of the durability of
plant resistance to PPs as having the polygenic (horizontal)
character. The suggestion as to durability of monogenic (vertical)
resistance needs to be proved. When operating with plant resistance
to PPs, it should, however, follow the phenotypic display of this
trait, rather than by speculations as to the number of the genes
being engaged.
The practical implications from these speculations are the
following:
viii) It needs to evaluate plant resistance to PPs (CESPPs
A.2.1.) in the provocative for PPs environmental (laboratory and
field) conditions. Importantly, it should take into account not
only numeric scores of affection, but also values of crop’s
yielding, practicing the pesticidal check.
ix) It needs to maintain CESPPs A.2.1. of a cultivar by
artificial selection of resistance plants in conditions of
increased infectious loading at seed farming.
It should recall that CESPPs 2.1. (A.2.1.) “Plant resistance to
PPs” is durable on condition that the presence of the following
prerequisites:
2.1.1.P.1. (A.2.1.1.P.1.) A hereditary ability of a plant taxa
(species, subspecies, phenological forms, varieties strains,
hybrids, lines) to resist against a given taxon of PPs,
2.1.1.P.2.(A. 2.1.1.P.2.) Level of physiological state of a
host-plant, which is close to proper one.
2.1.2.P.1. In biocenoses, forming of a dominant stock at the
natural conditions.
A.2.1.2.P.2. In articenoses, a resemblance of a dominant stock
to that in biocenoses or special cultural practices with the aim of
effective operation of CESPPs A.2.1.2.
8.2. Anthropic-2
8.2.1. Cultural practices disturbing physiological state of
dominants and obstacles for host-plant superevasion
Breakage of the prerequisites:
2.1.1.P.2. A level of physiological state of a host-plant, which
is close to proper one
2.1.2.P.2. In articenoses, a resemblance of a dominant stock to
that in biocenoses or special cultural practices with the aim of
effective operation of CESPPs A. 2.1.2.
8.2.1.1. CESPPs 2.1.1.1.1.3, 2.1.1.2., A.2.1.1.2., 2.1.1.3.1.2.,
A.2.1.1.3.1.2., 2.1.2.1., and A.2.1.2.1. failed
8.2.1.1.1. Affection by phytopathogens and herbivores
R. Painter (1951) has considered the resistance of trees to
pest insects as a special category of this trait – a physiological
resistance. It might be this view is a reflection of the fact that
the proper physiological state of trees as a prerequisite of
resistance in forest trees occurs to be disturbed very often.
The causes, why silviculture concedes agriculture in maintenance
of the proper physiological state of plants, consist in two
realities. Firstly, it is difficult to control the state of
perennual trees growing often in environmental conditions far from
optimum for a given tree species. The second, in agriculture in
field, defects of cultural practices become obvious in the same
year or within few years. Therefore, the defects of cultural
practices can be revealed easily.
Contrary, in silviculture, the improper cultural practices bring
their fruits often through dozens of years. Obviously, it is
difficult to reveal true causes of weakening of physiological state
of these, if the grounds of that were laid many years ago. In this
human activity, articenoses with improper composition of plants are
often established, so that the prerequisites 2.1.2.P.. and 2.2.1.P.
become disturbed that lays obstacles, in particular for operation
of Superevasion and activity of natural enemies.
Due to above peculiarities of silviculture, the cultural
practices in this province are characterized by the vast number of
defects. It is necessary for growing of healthy forest to bring the
defects on light. On the other hand, over centuries of its
existence, forestry has developed measures, which allow
establishing stable forest ecosystems even in severe environmental
conditions. Unfortunately, the achievements of forestry often are
not used in practice.
In silviculture, FDESPPs 8.2.1. "Cultural practices disturbing
physiological state of dominants and obstacles for host-plant
superevasion" includes a wide diversity of activities and operates
in complexes with many other FDESPPs composing diverse
combinations, in particular with 8.2.3., 8.2.4., 8.2.5., 8.2.6.,
8.2.7., 8.3.1., 8.3.2., 8.3.3., 8.3.4., 8.3.5., 8.3.6., 8.4.1.,
8.4.2. Therefore, later in this text, it will be numerous returns
to this FDESPPs, when considering of a cooperation of FDESPPs and
their complex effects.
Because the management in agriculture is controlled much better
than that in silviculture, the cases of improper cultural practices
in the former are rather rare. Nevertheless, the affection of the
winter wheat by the frit fly, Oscinella frit due to improper
cultural practices have been demonstrated by G.I. Vasechko (2001).
In the one case, the winter wheat was grown in the special test
with the diverse practices. In plots with surface tillage instead
of digging up and absence of fertilization, value to tillering
occurred to be low, percentage of tillers colonized by Oscinella
frit was much greater than that at proper cultural practices
(normal digging up and fertilization).
In the other case, the winter wheat was sown the large delay and
on the exhausted soil (after harvesting of the sugar beet). These
circumstances resulted in the same effect as that in above example.
It had to re-sow this field.
These examples suggest that in agriculture, maintanance of the
level ESPPs A.3.1."Proper control" needs in strict providing an
operation of prerequisites of CESPPs A.2.1.1.3. and A.2.1.2.1.
"Superevasion" both against herbivores and phytopathogens. The
usage of optimal sowing dates of winter and spring crops allows
decreasing of density of herbivores and affection by phytopathogens
to the Insignificant values.
8.2. Anthropic-2
8.2.2. Changes in the soil conditions unfavorable for
dominants
Breakage of the prerequisites:
2.1.1.P.2. A level of physiological state of a host-plant, which
is close to proper one
8.2.2.1. CESPPs 2.1.1.1.1.3., and 2.1.1.2.1.2. failed
8.2.2.1.1. Outbreaks of stem borers
The disturbance of physiological state of plants is common at
sharp change of water regime of the soil. The changes take place at
building of large water reservoirs (storage lakes on rivers) and
drainage of swamps. The reservoirs induce a lifting of the water
table, which exerts destructive effects of forest sometimes on
dozens kilometers outside of them. In a result, roots of the trees
growing in depressions occur continually in the water and die off.
The mortality of dominants takes place in riparian forest growing
on banks above dams in river’s valleys. Below dams, riparian forest
suffers due to cessation of flooding. Such causes of physiological
state of trees operate, in particular in Ukraine in vicinity of the
River Dnieper. On this river, it has been built several giants
reservoirs, which established a number of problems of the
above-mentioned character. After building of the grandiose Kakhovka
storage lake on the River Dnieper, the water table on the level
side of the Dnieper Valley rose on the distance thirty km for
fifteen years (Skaballanovich et al., 1979, p. 163).
The dieback and decline of trees are common on edges of a forest
with clear-cut areas in the humid habitats. Until integrity of a
forest massif is not disturbed, the water table stays on admissible
for tree vitality depth, because trees draw off water from the
soil. Contrary, after clear cutting, a water table lifts on the
soil surface, and a clear-cut area becomes a swamp. The latter
spreads in a near by forest, and trees in the range of a swamp die
off.
At drainage of territory, a water table brings down and stays
continually on a low level. In Soviet Union, digging of trenches in
swamps and humid forests was practiced often. The grounds of such
activity consist in an intention of the powerful Ministry of
Melioration to have objects, which prove necessity of existence of
this monster.
At absence of drought over several years after digging of the
trenches, the trees are able to spread their roots to the lowered
level of the water table and to survive. Contrary, at drought in
this period, the roots dry out and the trees die.
8.2. Anthropic-2
8.2.3. Damage of dominants by people or animals under human
assistance
Breakage of the prerequisites:
2.1.1.P.2. A level of physiological state of a host-plant, which
is close to proper one
2.2.2.P.1. Proper activity of predators, which operates in
cooperation with CESPPs of the category 2.4. Periodic (bottle-neck)
suppression
2.2.2.P.2. A size of area of an ecosystem sufficient for
providing of predators with vital requirements
8.2.3.1. CESPPs 2.1.1.2.2. ,2.1.1.1,1.3., 2.1.1.2.1.2. , and
2.2.2. failed
8.2.3.1.1. Affection by phytopathogens and herbivores
A mechanical control of weeds, which is conducted in afforested
areas annually until closing of their canopy, it is common damage
of young stems. Again, these wounds serve as an entrance for
infection. Therefore, application of herbicides is prospective for
control of weeds.
The heavy techniques, which are used for withdrawal of cut
trees, exerts damage of roots of reserved trees and wounds their
stems. The damage is most destrictive, when tree cutting is
conducted in warm period of year. In Tsarist Russia, it was
conventional to conduct all kinds of wood cutting in winter. In
Soviet Union and Former Soviet Union, all kinds of wood cutting are
conducted the whole year round. In so doing, timber becomes
endurable to rots.
In forests, which are often visited by people, for example those
of a recreative concern, it is common suppression of vitality of
tree’s roots due to trampling down of the soil, that result in
dieback or mortality of trees.
As to wild hoofed animals, a lack of their predators and
insufficient hunting lead to heavy damage of young trees. In
addition, the great damage is inflicted by cattle. Grazing of
cattle in forest is practiced widely in this country. Protection of
a young generation of forest from the grazing is limited by
plantations until closing of their canopy. After that, cattle is
able to penetrate into plantations freely. It is supposed to be
this is the main cause of affection of oak stems with the stem
cancer, which produces large tumors (Rudnev et al., 1975).
8.2. Anthropic-2
8.2.4. Affection by air pollution
Breakage of the prerequisites:
2.1.1.P.2. and A. 2.1.1.P.2. A level of physiological state of a
host-plant, which is close to proper one
8.2.4.1. CESPPs 2.1.1.1.1.3., 2.1.1.2.1., A. 2.1.1.2.1., and
A.2.1.1.2.2. failed
8.2.4.1.1. Outbreaks of stem borers in forests and signs of
diseases affecting agricultural crops
Now, it is not popular to explain the forest decline by
weakening of forest at improper silvicultural practices. The main
cause of the decline is supposed to be air pollution. This idea may
be seen in the quotation from W. Baltensweiler (1985,
p. 77): "The risk of outbreaks of bark beetles and forest
defoliators is enhanced in polluted ecosystems, either due to the
reduced vigor of the trees and/or altered characteristics of the
host-plants. The long lived trees are at a selective disadvantage,
therefore air pollution must be stopped and any insect impact,
which generally accelerates the "Waldsterben" should be avoided"
(p. 77, Summary).
The role of air pollution comparing with other stressors is,
however, unclear that may be seen in the following quotation:
"Since World War II repeated outbreaks, snow breakage and air
pollution combined caused the destruction of more than 100 000 ha
(Wentzel, 1982)" (Ibid., p. 81). This phrase suggests that
"repeated outbreaks, snow breakage and air pollution" are
independent phenomena."
As to conversion of mixed beech-silver fir forest into
overstocked spruce monocultures and exhaust of soil resources at
withdrawal of wood biomass, when cutting mentioned in the cited
paper, this is an obvious cause of repeated outbreaks and snow
breakage in Middle Europe. Contrary, the role of air pollution in
the wide-scale forest decline is not obvious.
It seems air pollution has become idèe fixe at explanation of
the forest decline. It should stress that effect of air pollution
is well detected by its location in vicinity of large industrial
enterprises. Further, it is characteristic for countries of the
Former Communist Block, where authority ignores protection of the
environment.
As an example of such a situation, it can serve the report by
V.V. Fomin and S.A. Shovnin (2001). The studies were
conducted in a region of a copper-melting plant in the Sverdlovsk
Region (Russia). It was shown that the heavy affection of forest
spread eastward the plant - up to 20 km as an entire area. Farther,
signs of the affection were recorded in separate plots of fewer
areas. This disposition of the affected areas was due to the
direction from the west of the prevailing winds in this area.
Westward the plant, the affection spread only on 5 km.
This report is consistent with the view by W.H. Smith
(1981). He has supposed that "Severe impact of air pollutants on
forests are dramatic, but judged relatively unimportant because of
their extremely localized nature" (cited
in W. Baltensweiler, 1985, p. 77).
In the publication, which probably expresses the view of United
Nations Organization, the pollution, although of another kind, is
considered as the only cause of Waldsterben in the industrial
countries (Horstkotte, 1995). This pollution is of the kinds of
exhaust gases and spoiled subsoil waters. Such pollution is
important as to human health, but its concern to Waldsterben is
dubious. If this view would true, mortality of trees would affect
first of all shade trees in settlements and road-side plantings.
However, Waldsterben takes place just in exploiting forests, whose
state is determined by silvicultural practices independently on
distance from the exhaust gases and spoiled subsoil waters. The
polluted subsoil waters cannot penetrate in mountain forest, which
often undergoes the decline, in particular in Germany. The exhaust
gases are hardly are able to kill the trees in remote mountain
forest. Being such poisonous, the gases would depopulate all the
settlements.
Again, the measures, which have been proposed in the above
article to counteract the forest decline, are wrong. The measures
are limited by a decrease of output of carbon dioxide (Ibid.,
p. 2). Firstly, the issue of carbon dioxide output is neither
air pollution, nor subsoil water pollution. Secondly, the
dependence of severity of droughts on output of carbon dioxide is
very dubious. Here are examples of a lack of the dependence. In
IX‑XI centuries, the technology was too weak to effect on
climate. Nevertheless, climate in the region of North Atlantic was
warmer than that now. Contrary, XVI‑XVIII centuries are known as
the Little Ice Age. In the peak of the cold and wet period, when
size of glaciers in Switzerland reached maximum, and the Rhone
River is south France was caught many times by ice (1556‑1595). In
the same period, the western areas of North America suffered due to
the severest drought. It continued over twenty years (1570‑1590),
and the values of precipitation composed over 20% of those typical
for XX century (Le Roy Laburie, 1971, pp. 213‑215).
Notably, that the sequoia trees, which at present time are close to
1000 years old, have survived this stress, as well as the
forest biome as a whole.
Further, air pollutants can serve as nutrients for plants. Here
is the citation from D.P. Ormrod (1978, p. 22): "White
pine seedling productivity increases with decrease in pH of
simulated acid rain from 5.6 to 2.3. in spite of near depletion of
available K, Mg and Ca ions in the soil at pH 2.3. (Wood and
Bormann 1977). Additions of HNO3 to the simulated rain are
associated with increased foliar N concentration."
Another report about beneficia