Responseofpeachtreegrowthandcroppingtosoilwater ...l(lurnal ofHorticultural Science (1989)64(5)541-552 Responseofpeachtreegrowthandcroppingtosoilwater...

l(lurnal of Horticultural Science (1989) 64 (5) 541-552

Response of peach tree growth and cropping to soil waterdeficit at various phenological stages of fruit development

By S.-H. LI,J* J.-G. HUGUET,l P. G. SCHOCHJ and P. ORLAND<YJI.N.R.A.-S.R.I.V., Domaine de Gotheron, 26320 St Marcelles Valence, France

zI.N.R.A., Station d' Agronomie, Centre de Recherche Agronomique d' Avignon, 84140Montfavet, France

JI.N.R.A., Station de Bioclimatologie, Centre de Recherche Agronomique d'Avignon, 84140Montfavet, France

SUMMARY

Four- and five-year-old 'Merrill Sunda~ce' peach trees, protected from rainfall by poly-ethylene film covers, were fully irrigated using micro-sprinkler (irrigatio~ schedulingbased on a tensiometer technique), or subjected to water stress at different phenologicalstages of fruit growth. Water deficit imposed during the first phase of rapid growthsignificantly increased fruit size at harvest during two experimental years when comparedwith the control full-irrigation treatment, while smaller fruits were produced from treesreceiving an imposed water deficit during the final accelerated fruit growth, or throughoutthe fruit development period. When water deficit was applied to the trees during the pithardening phase and the first two phases of fruit development, fruit size was not affected.However, shoot extension growth and limb diameter increases were limited wheneverwater supply was restricted. After-effects on limb expansion growth and benefits of waterstress on fruit growth were obvious during the post-stress period. Moreover, prematurefruit drops after the June-drop were reduced for all the water stress treatments. The levelof total soluble solids was higher in fruits from the trees subjected to water stress duringthe final rapid phase of fruit growth, and flower bud production was improved on treesgiven a restricted supply of water during the critical period of flower bud induction.

~

IT is widely acknowledged that field crops suchas wheat, maize, sorghum and pea are moresensitive to water stress at particular stages ofdevelopment (Begg and Turner, 1976; Grignac,1985). At these critical stages, for example atflowering for peas (Hiler et aI., 1972) and atgrain swell for sorghums (Langlet, 1973), arestricted water supply reduces crop yield mostseverely.

With fruit trees, there is little quantitativeinformation on their cmpping responses towater stress at different phenological stages.Chalmers et al. (1984) concluded from previousexperiments on peach and pear trees thatreduced water supply during the early stages offruit growth until the end of shoot growth, didnot affect final fruit size, number or yield.

.Permanent address: Horticulture Department, HuazhongAgricultural University, Wuhan, People's Republic ofChina.

.o1t

Nevertheless, Vidaud et al. (1987) consideredthe period from the beginning of fruit pit hard-ening until the end of shoot growth in peachtrees to be a critical phase for fruit size and yieldresponses to water supply. The effects of waterstress during the final stage of rapid fruit growthon final fruit size have been reported as eitherof little importance (Irving and Drost, 1987) orremarkable (LOtter et aI., 1985).

All these investigations on fruit trees wereconducted under natural condition. Since thewater requirements of fruit trees are relativelylow during the first and second phases of fruitdevelopment (Li et al., 1989a), a little rainfallduring these periods can remove the water.stress status in trees. Therefore, a strict experi-mental control of soil water status is required todetermine the effects of water deficit on fruittrees at different phenological stages.

This paper reports an experiment designed to

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-. --~-

542 Soil water deficits and peach

elucidate the behaviour of peach trees growingin the field under water stress at different phe-nological stages, carried out under the protec~tion of polyethylene film covers for theexperimental plot. We studied.in particular:first, tree growth, such as shoot extension andstem diameter expansion, and fruit growth pat-terns, secondly, fruit bud production, fruit dropand yield and thirdly, fruit quality and fruitstorage.

MATERIALS AND METHODS

Experimental site and plant materialsThis study was conducted during the growing

season of 1987 and 1988 in the, Gotheronexperimental orchard ofthe Institut National dela Recherche Agronomique near Valence in themiddle Rhone Valley of France. The orchardsoil was stony alluvial with the mechanical com-position of 15% clay, 30% silt and 54% sandafter removing the stones. Field capacity wasabout 17% and wilting point about 8% byweight.

The materials selected for this trial were pea-ches, cv. Merrill Sundance (Prunus persica (L.)Batsch), a late ripening cultivar on 'Rubira'rootstock planted in the spring of 1984. The

trees, trained in a double Y conformation, wespaced 3.5 m apart within the rows and 5apart between rows.

Irrigation treatmentsA 0.1 ha surface area of the orchard was PI'

tected from rainfall from 24 April 1987 (8after full bloom) to 22 September 1988 (aftthe harvest) by using covers of black polethylene films (6 or 8 m width and 200 J.l.mthicness) (Figure 1). Th~ ridges under the trwere about 2.2 m wide, supported on a frabout 0.6 m high which consists of fiat irarches (gauge: 5xl4mm) and 'Provenreec!s: the ends of the arches (0.1? cm Ionwere pushed into the ground and all the archwere bound toge~her with seven parallel 1'0of 'Provence' reeds aligned along the. tre~ 1'0.Water could thus be supplied by micro-spriklers (two per tree) which wetted an area abo1.2 m in diameter at a discharge rate of 20 Ih-The junctions of two polyethylene films.which 'Provence' reeds were:wrapped were ti ,to the arches, one:Ove1't.Qeother, and the abofilm was cut to accommodate the tree truand also to permit control of water applicatio

Six treatments were applied respectively

FIG. 1Covers protecting the experimental plot from rainfall. The arrow indicates the junction of two polyethylene films.

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Trunk gi{th Tree crown sizeIrrigation (cm) (m3)Y

Control 25.1 :t 0.& 5.8 :t 0.31st PWS 26.2 :t 0.5 6.3 :t 0.42nd PWS 25.5 :t 0.9 6.1 :to.43rd PWS 25.3 :t 0.8 5.7:t 0.21+ 2 PWS 26.6 :t 1.0 6.2 :t 0.21+2+3 PWS 25.4 :t 0.5 5.3 :t 0.4

S.-H. LI, J.-G. HUGUET, P. G. SCHOCHand P. ORLANDO

six rows of 7 to 10 trees, selected for uniformityof the trunk girths and tree crown size (Table I).No guard rows were used and a root-cuttingtreatment was carried out, down t050 em, halfway between the rows, before the film coverwas installed, to limit crossed-root effects. Thesix treatments applied were as follows:

A: control. Trees were irrigated wheneverthe mean of the soil water potential, derivedfrom the readings" of three tensiometersinstalled at 0.5 m depth and 0.5 mfrom theemitters, reached. about -60 kPa. The soilwater potential usually rose to about -lO,kPaafter irrigation. The first irrigation wasapplledon 8 May 1987 andon 3 May 1988;

B: water stress during the firs.t phase of fruitdevelopment (1st PWS). Trees did not receiveany water. during the first stage of rapid fruitgrowth (for description of the fruit develop-ment phases, see the reviews of Bollard (1970)and Romani and Jennings (1971», and werethen irrigated as in treatment A;

C: water stress during the second phase of fruitdevelopment (2nd PWS). Irrigation occurred atone-third the frequency of treatment A duringthe stage of fruit pit hardening. For the remain-ing time, the irrigation scheduling was asapplied in treatment A;

D: water stress during the third phase of fruitdevelopment (3rd PWS). Irrigation was appliedat one-third the frequency of treatment Aduring the final stage of rapid fruit growth. Forthe remaining time, the irrigation schedulingwas as applied in treatment A;

E: water stress during the first two phases offruit development (1+ 2 PWS). Irrigation sched-uling was the same as in treatment B for the first

TABLEITrunk girths and tree crown sizes before the differential

irrigation treatments were started

111

.Average followed by standard deviation.yTree crown size (V) estimated according to:

V = (D2 x H)/8where D is the mean crown diameter (average of S-N diam-eter and E- W diameter), H the crown height (Zhang et af. ,1979).

543

phase, as in treatment C for the second phase,and as in treatment A for the last phase of fruitdevelopment;

F: water stress during the three phases of fruitdevelopment (1+2+3 PWS). Irrigation sched-uling was as in treatmentB for the first phase, asin treatment C for the second phase, and as intreatment D for the last phase of fruitdevelopment.

The volume of water applied during the twoyears at various stages for the six treatmentsand the dates of the start and end of the threephases are given in Table II.

MeasurementsEight shoots of the previous season per tree

were marked in both years at the 'beginning ofthe growing season. Their flower numbers andsubsequent fruitlets borne were controlled toestimate the stress effects on June drop. Afterphysiological drop of fruits, peaches were handthinne<ilO to 15 em apart on 22 June in 1987and on 13June in 1988, i.e. four or five peacheswere left on the long shoots (Vidaud andClanet, 1978; Mitcham, 1980). The remainingfruit lets after hand thinning and fruits at har-vest were counted for each tree, allowing thepremature fruit drop to be determined.

The total growth increment of all new shootson the previous season's shoots marked abovewas measured at the end of each phase in 1987,.but only the length of the terminal new shootswas measured in 1988. The rate of stem diam-eter expansion was assessed by dendrometermeasurement on two limbs per treatment in1987 and by the hand measurement on one limbper tree in 1988. The dendrometer system usedlinear variable displacement transducer(Huguet, 1985) mounted in an INVAR frameas described by Li et al. (1989a). Seven to tentagged fruits on. two previous season's shootsper tree were usually measured every week tofollow the fruit growth pattern. Measurementswere made on the peach suture between 0600and 0800 hours until harvest time.

All the fruits from each tree were weighed atharvest. On the first picking date, percentagesoluble solids were determined on ten fruits pertree with a refractometer. Moreover, a box of18 selected peaches, placed in the paper cells ofa honeycomb, per tree was examined at inter-vals for rot under home conditions.

TABLEIIVolume of irrigation water applied to 'Merrill Sundance'

peach trees during the different phases of fruit growth

Water applied (m3/ha)during fruit growth phase

Irrigation treatment I II III

1987Control 553 949 20691st PWS 0 949 20692nd PWS 553 388 20693rd PWS 553 949 8951+2 PWS 0 388 20691+2+3 PWS 0 388 895Phases: start 8 May 27 June 7 Aug.

end 26 June 6 Aug. 24 Sept.

1988Control 414 1059 18161st PWS 0 1059 18162nd PWS 414 364 18163rd PWS 414 1059 6201+2 PWS 0 364 18161+2+3 PWS 0 364 620Phases: start 3 May 29 June 10 Aug.

end 28 June 9 Aug. 22 Sept.


Flower bud density data were obtained bysampling flower bud number on eight shoots, 30to 60 cm long, per tree only in December 1987.

Statistical analysisThe replicated blocks in the present study

consisted of 7-10 single trees of each irrigationtreatment. Due to the absence of a randomizedblock arrangement, the method of one-wayanalysis of variance (Dagnelie, 1975; Zhang etal., 1979) was used in the statistical analysis ofthese data.

,.

RESULTSShoot extension growth

Water stress imposed during the first andsecond phase of fruit development respectivelyresulted in a significant reduction of shootextension growth during the stress period inboth years, as shown in Table III. The totalextension growth increment was reduced byabout 25% in 1987 (all the new shoots on theprevious season's shoot) and from 11 to 40% in1988 (terminal shoots). However, there wereno obvious differences in shoot growth duringthe second phase between the treatments 2ndPWS and 1+2 PWS, nor between the controltrees and the rewatered trees (e.g. treatment1st PWS).

Shoot extension growth stopped in mid-Julyor at the end of July for the trees of all the

treatments. Thus, the water stress imposedduring the third phase of fruit development didnot affect the shoot elongation of 'Merrill Sun-dance' peach trees. Even in the second year, thepotential of shoot growth during the first phasewas very similar between the control treatmentand 3rd PWS. At the end of phase I, an averageof 41.5 cm shoot growth increment was.recorded for the control trees in 1988comparedwith a 38.8 cm shoot growth increment for treesof the treatment 3rd PWS.

Limb expansion growth. All the water stress treatments stronglyreduced final stem diameter increment in bothyears if compared with the control trees (Figure2). Limb expansion growth under 2nd PWS and'3rd PWS treatments was limited as soon aswater stress was imposed on the trees. More-over, the final reduction of limb diameter incre-ment by restricted water supply was found todepend on the time at which water stress wasapplied to trees, but not on the duration ofwater stress or on the restricted amount ofwater finally applied.

All trees which had suffered water stressduring the first phase (treatments 1st PWS, 1+2PWS and 1+2+3 PWS) had a much smallerincrement of limb diameter than those water-stressed during the second or third phase.

The patterns of limb expansion growth were

TABLE IIIEffects of water deficit imposed during different phenologicalstages on the shoot extension growth of cv. Merrill Sun dancepeach trees, expressed as the extension growth increment ofall the new shoots per previous season's shoot in 1987 and the

extension growth increment of terminal shoot in 1988

Shoot groWth increment (em) duringIrrigation treatment phase I phase II

1987Control1st PWS2nd PWS3rd PWS1+2 PWS1+2+3 PWS

1988Control1st PWS2nd PWS3rd PWS1+2 PWS1+2+3 PWS

184.7 a'133,0 b191.8 a212.8 a153.0 b148.9 b

81.8 ab99.7 a61.0c82,2 ab68.4 be67.3 be

41.5 a33.6c39.6ab38.8 ab35.8bc36.9bc

16.6 ab13.4 be11.0 cd17.2 a9.9d

12.3 cd

'Figures followed by different letters are significantly dif-ferent at P = 0.05.

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S.-H. LI, J.-G. HUGUET, P. G. SCHOCH and P. ORLANDO 545

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FIG. 2Limb growth of 'Merrill Sundance' peach trees in 1987 (top) and in 1988(bottom) in response to water deficit applied during different phenologicalphases of fruit development: Control (8--.), 1st PWS treatment(0---0), 2nd PWS treatment (A-A), 3rd PWS treatment(6---6), 1+2 PWS treatment (8-8) and 1+ 2+3 PWS treatment

(0---0).

very similar between the trees of treatments 1stPWS, 1+2 PWS and 1+2+3 PWS, with nomarked differences in final increment of limbgrowth, except that ofthe 1st PWS treatment in1988. For trees in this treatment, limb diameterincreased more rapidly during the last phasethan those of the other two treatments.

Trees in the 3rd PWS treatment, with areduced amount of water of 1174 m3ha-1applied in 1987 and of 1196m3ha-1 in 1988, hada greater increment of final limb diameter thanthose of the 1st PWS treatment with a reducedwater volume of 553 m3ha-I in 1987 and 414m3ha-I in 1988.

Fruit growth and fruit size at harvestSeasonal fruit growth of 'Merrill Sundance'

peaches shows a classical pattern of three dis-tinct growth periods (Figure 3).

In 1987, water stress imposed on trees did notinfluence fruit growth until the end of thesecond phenological phase: there were no sig-

. nificant differences in fruit size between all thetreatments before 1 August. On 7 August,fruits on the trees of treatments 2nd PWS and1+ 2 PWS were significantly smaller than thoseon the control trees. Unlike the effect of pre-vious treatments, fruits of the 1st PWS treat-ment were larger than the control ones. Waterstress imposed during the phase III limited fruitgrowth, resulting in a significantly smaller fruitsize in the treatment 3rd PWS from 2 Septem-ber. However, ftuit size in the treatments 2ndPWS and 1+ 2 PWS became similar to that inthe controls about 1 and two weeks after remov-ing the water stress. This similarity in size wasthen maintained until maturity.

In 1988, treatment effects on fruit develop-ment were similar to those in 1987, except with

'lst PWS. From early July, the fruit diameter onthe trees of this latter treatment was signifi-cantly greater than that of the other treatments,including that of the control treatment.

At harvest, fruit size was considerably


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FIG. 3Fruit growth of 'Merrill Sundance' peaches in 1987 (top) and in 1988 (bottom)in response to water deficit applied during different phenological phases of fruitdevelopment: Control (8-8), 1st PWS treatment (0---0), 2ndPWS treatment (A-A), 3rd PWS treatment (6---6), 1+2 PWStreatment (8-8) and 1+2+3 PWS treatment (0---0). Vertical

bars represent L.S.D. at P = 0.05.

improved by the treatment 1st PWS, anincrease of 12 g in both years, when comparedwith that of the control treatment (Table IV).By contrast, significantly smaller fruits wereobtained on the trees of the treatments 3rdPWS and 1+2+3 PWS. A decrease of 1~14 gin 1987 and 12-15 g resulted from the two pre-vious water-stress treatments. As in treatments2nd PWS and 1+ 2 PWS, water deficit had littleeffect on the final fruit fresh weight.

Fruit-set and crop yieldEffects of water deficit applied at different

phenological stages on fruit-set were evaluated

L

by studying fruit drops of June and pre-harv(Table IV).

Water stress imposed on peach trees did nenhance the"ir June-drop. In 1987, fruit-setwater-stressed trees (treatments 1st PWS, 1PWS and 1+2+3 PWS) was 20.6%, a valsimilar to that with normally irrigated tr(mean of control, 2nd PWS and 3rd PWS trements). In 1988, the extent of fruit drop inwater-stressed trees was similar or less imtant than that of the control trees, although'significant differences existed.

However, water deficit at every stageduring all stages of fruit development improv

S.-H. LI, J.-G. HUGUET, P. G. SCHOCH and P. ORLANDO 547

TABLEIVInfluence of water deficit imposed during different phenological stages of fruit development on the cropping characteristics of cv.

Merrill Sundance peaches

Fruit Fruit drop Mean Fruit budJune fruit number prior to Fruit fruit number per

Irrigation drop' after maturity' production weight m shoottreatment ('Yo) thinning ('Yo) (kg/tree) (g) length

I

1987Control 75.5b' 122.7 a 16.4 a 16.71ab 164.1 b 45.8b1st PWS 77.3 b 120.0 a 7.6b 19.64 a 176.1 a 48.3 ab2nd PWS 76.1 b 122.0 a 5.3b 19.39 a 167.5 b SO.3a3rd PWS 85.0 a 92.5b 5.0b 13.68 b 154.0 c 48.0 ab1+ 2 PWS 77.5 b 124.0 a 7.5 b 19.01 a 165.9 b 49.9 a1+2+3 PWS 83.3 a 85.1 b 5.0b 12.16 b 150.5 c 49.7 a

1988Control 60.0 370.0 6.3 43.75 126.2 b1st PWS 60.2 350.0

*'6.8 45.16. 138.5 a

2nd PWS 51.6 383.0 3.4 44.84 121.0 be3rd PWS 46.9 380.9 4.7 42.18 116.2 cd1+2 PWS 57.2 353.8 4.5 42.00 124.3 bc1+2+3 PWS 55.7 326.0 2.2 35.35

.110.9 d

,From full bloom to the end of physiological drop., From hand thinning after fruit physiological drop to harvest.,Figures followed by different letters are significantly different at P = 0.05.

fruit set after June drop in 1987. A significantlymore important fruit drop after the June phys-iological drop to maturity was found with thecontrol trees than the water-stressed ones. Thiseffect on premature fruit drop disappeared in1988. For this second year, few fruits droppedprior to maturity on all the experimental trees,including the control ones, and no significantdifferences were observed.

In 1987, fruit drop and fruit size werereflected in crop yield. A yield increase of 14 to18% was recorded on the trees under the treat-ments 1st PWS, 2nd PWS and 1+2 PWS whencompared with the fruit production of the con-trol trees, but this improvement was statis-tically significant only at about P = 0.10. Inaddition, a lower yield, a decrease of 18 to 27%compared with the control, was obtained on thetrees under 3rd PWS and 1+2+3 PWS treat-,

\II

TABLE VContent of the total soluble solids of cv. Merrill Sundance

peach fruits (first picking) related to irrigation treatment

Soluble solids ('Yo)in 1987 in 1988Irrigation treatment

12.8 be'12.5 c13.0 ab13.2 a12.8 be13.2 a

13.2 be13.6 ab13.1 c14.1 a13.3 be13.7 ab

Control1st PWS2nd PWS3rd PWS1+2 PWS1+2+3 PWS,

Figures followed by different letters are significantly dif-ferent at P = 0.05.

.

ments, because of a lighter load of total fruitletsafter hand thinning (Table IV) resulting fromthe greater June fruit drops, and smaller fruit.In 1988, there were no significant differences inyield. However, the trees of the 1+2+3 PWStreatment produced about 16-22% fewer fruitscompared with the others.

Fruit qualityTrees subjected to water stress only during

the third phase (treatments 3rd PWS and1+2+3 PWS) produced fruits with higher totalsoluble solids at harvest in both years than didthe control trees (Table V). However, waterstress imposed to trees during phase I or II, orphases I and II had no obvious effect on thecontent of soluble solids in the fruits.

Water stress treatment applied during thethird phase improved fruit keeping capacity

TABLEVIRate of flower-induced buds (flower buds/total buds) of cv.Merrill Sundance peach trees in 1987 related to irrigation

treatment

Irrigation treatment Rate of flower-induced buds ('Yo)

51.6 c'56.2 be59.7 ab55.0 be59.6 ab61.5 a

Control1st PWS

'2nd PWS3rd PWS1+2 PWS1+2+3 PWS

'Figures followed by different letters are significantly dif-ferent at P = 0.05.


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FIG.4Peach fruit (the first picking) keeping capacity in the house condition in response to water deficit applied duringdifferent phenological phases of fruit development in 1987 (left) and in 1988 (right): Control (8-8). 1stPWS treatment (0---0), 2nd PWS treatment (A-A), 3rd PWS treatment (6---6).1 +2 PWStreatment (.-.) and 1+2+3 PWS treatment (0---0). Vertical bars represent L.S.D. at P = 0.05.

(Figure 4). Under home condition, fruits fromthe trees of the 3rd PWS and 1+2+3 PWStreatments rotted significantly less rapidly inboth years than did control fruits. At the end ofthe fruit keeping trial (1(}-14d after picking),about 4(}-50% of rotten fruits were recorded,for the control treatment, but only 12-30% forthe first two treatments. Water stress appliedduring the first two phases did not significantlyaffect peach fruit keeping capacity. In 1987, nosignificant differences were found between thecontrol treatment and the 1st PWS, 2nd PWSand 1+2 PWS ones. In 1988, however, fewerrotten fruits after picking were obtained on thetrees of the 1+ 2 PWS treatment as comparedwith control fruits.

Fruit bud productionWater stress imposed on peach trees during

any stage of fruit development did not decreasefruit bud formation (Table IV). On the con-trary, the trees given treatments 2nd PWS, 1+2PWS and 1+2+3 PWS produced significantlymore dense fruit buds than the control trees.

DISCUSSION

The final size of peach fruits depends

basically on the cell number and size in tbmesocarp. Unlike shoot elongation and trunor limb expansion growth, cell division in t~mesocarp does not occur throughout frudevelopment, and cell enlargement is non-pngressive. Cell division occurs only during tlfirst growth period, starting about 20 days aft,full bloom and lasting about 40 days, whirapid cell expansion occurs during the lagrowth phase (Jackson, 1968; Bollard, 197(We have reported (Li et aI., 1989c and 1989that, under conditions of intense water stre!the growth rate of peach fruits was not ataffected during phase I, although a very lcwater potential of leaves and stomatal clostwere observed on these trees, while fruit exp~sion was significantly limited by water denduring the final growth phase. This resultconfirmed by the present study (Figure 3), SIgesting that cell enlargement appears more $Isitive to water stress than cell division (Hsi1973; Begg and Turner, 1976). Moreoverperiod of water stress imposed on peach trduring the first two phenological phases of fldevelopment favoured fruit growth a~removal of the water stress status in the tr(Figure 5). This favourable effect on f

:J: Z I I------ CONTROL

0---0 1 ST PWS-- 2 ST PWS

----- 1+2 PWS..~

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w 8~w0::0~I- 6~J:I/)w0::.....

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FIG. 5Daily rate of fruit fresh weight increase during post-stress period in1987. Fruit fresh weight was estimated according to fruit diameter:y

= 2.99<°05'U.)(y: fruit fresh weight in g, x: fruit diameter in mm) whichis obtained in the laboratory by sampling fruits on the guard trees at

intervals. Vertical bars represent L.S.D. at P = 0.05.

growth during the post-stress period, alsoobserved by Chalmers et ai. (1981) and Mitchelland Chalmers (1982), is difficult to explain.Since the rate of cell enlargement is dependenton its gross extensibility and turgidity status'(Green, 1968; Hsiao, 1973) and the cellturgidity status in those water-stressed fruits isthe same as in the control ones during the post-stress period, it is possible to suggest that cellextensibility would be increased. This effectmay be due to the violent changes of waterstatus in the cells, from a good turgidity statusto an important water deficit, or inverselyduring the period of water stress or at themoment of water stress removal.

The response of shoot elongation andincrease in limb diameter to water stress isclearly distinguished from that of fruit growthas described above. On one hand, shootelongation and limb diameter increase. wereimmediately inhibited whenever water supplywas restricted (Table II and Figure 2). On theother hand, the after-effect of water stress onlimb growth was obvious (Figure 6). During thepost-stress period, growth recovery for the

trees under treatments 1st PWS, 2nd PWS and1+ 2 PWS was never marked in 1987. Asregards shoot extension growth, neither after-effect nor favourable action of water stress wasevident during the post-stress period (Table II,comparison between the control and 1st PWS).

Leaf growth is often reported to be quitesensitive to water stress (Hsiao, 1973; Begg andTurner, 1976). Mild stress is enough to reducethe development of leaf area. However, theexpansion growth of leaves in peach trees isonly slightly sensitive to water stress (Li et af.,1989d). . At the water deficit imposed in thepresent experi~ent, water stress had no effecton the leaf surface area (results non-reported).

It is evident from the present study that thegrowth tolerance to drought varies with the dif-ferent organs of peach trees (Li et ai., 1989d).Based on the intensity of the growth inhibitionby water deficit; the sensitivity of organs towater stress may be placed in the followingorder of severity: limb diameter increase>shoot elongation growth> fruit growth >expansion of leaf area.

We had reported that a low level of water

8-- CONTROL

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FIG. 6Daily rate of limb diameter increase during post-stress period in 1987.Samples taken from dendrometer measurements on two trees in eachtreatment before the onset of stem shrinkage. Each point represents the

mean of the growth of three days.

supply might partly prevent premature fruitdrop in peach trees compared with high levels(Li and Huguet, 1989; Li et aI., 1989a). The1987 results in the present study show thatwater stress applied at any period also pre-vented fruit drop from hand thinning after theJune physiological drop to maturity (Table IV).In 1988, the premature fruit drop of the controltrees was slight, with a consequent absence ofsignificant differences in premature fruit dropbetween the control trees and the water-stressed ones. This phenomenon might beexplained by relatively dry soil conditions in thecontrol treatment plot. The micro-sprinklerswetted only about 13% of the experimentalsurface area. The remaining area was kept verydry, particularly in 1988, as a result of thecovers protecting the experimental plot. Thisexplanation can be supported by a trial on thesame cultivar in the same orchard. Trees of thesame age under natural conditions without filmcover protection, also irrigated by micro-sprin-

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,"

klers according to soil water potential (Isiometermethod), had a39.5% prematurefdrop in 1988 (unpublished data).

The most pronounced effect of frequent igation and abundant water supply'improved fruit size (Guelfat-Reich and BArie, 1980; Daniell, 1982; Panine and Meria1985), the reduction in total soluble solid ctent in the harvested fruits and in the fstorage capa<;ity (Guelfat-Reich et aI., ISGuelfat-Reich and Ben-Arie, 1980; LOtteal., 1985; Irving and Drost, 1987). Our resuhowever, demonstrate that reduced W1supply during the first two phases of f.development did not affect final fruit Sizfharvest (Table IV), which agrees with CImers etal. (1984), nor fruit quality (Table V:Figure 4). The smaller size, higher level!total soluble solids and longer storage duralafter picking were characteristic of the frfrom trees subjected to water stress at thephase of fruit development.

S.-H. LI, J.-G. HUGUET, P. G. SCHOCH and P. ORLANDO

The density of flower bud productionincreased on the trees of the treatments 2ndPWS, 1+2 PWS and 1+2+3 PWS (Table IV).The study of the rate of flower-induced buds(ratio of flower buds to total buds) showed thatthis high density of flower buds was due to thestimulation of flower bud induction', in thesewater-stressed trees (Table VI). A significantcorrelation was found between the density offlower bud (y) and the rate of flower-inducedbud (x):

y = -44.5 + 2.09x (r2 = 0.901, P<O.OOl).*'Since full floral induction occurs from the end

of June to the first ten days of July for peachtrees in our region (Li et al., 1988 and 1989b),we can suggest that flower bud formation can beimproved only by water deficit applied duringthe critical period of flower bud induction.

ConclusionThere is considerable evidence that a period

of water deficit applied to peach trees duringparticular stages of fruit development is some-times beneficial. It is possible to control vigourof peach trees without reducing fruit size andyield and without affecting fruit quality by usingdeficit irrigation during the first rapid fruitgrowth and fruit pit hardening phases. Conse-quently, water consumption and time of prun- ,

551

ing may be reduced. Since a short water stressimposed during any phase can partly preventpremature fruit drop, fruit production mayincrease on water-stressed trees compared withthe normally irrigated ones. By improving fruitsize at harvest, water deficit during the firstphase is more useful than if applied during fruitpit hardening or during the first two phases.

. Although water deficit during the final fruitgrowth phase can improve fruit quality andstorage capacity, and reduce premature fruitdrop, the small fruits at harvest limit the appli-cation of w~ter deficit during this period exceptin peach cultivars with extra large fruit (e.g.fruit of 170 or 200 g). For these, a slight reduc-tion of fruit size, or even a fruit weight reduc-tion of 20 or 30 g at harvest does not diminishtheir market value. On the contrary, in somecountries such as France, fruits of moderatesize are sold more readily and at a good price.

We thank Mr C. Bussi (Engineer of INRAGotheron experimental orchard) for his con-stant support during this work, Mr C. Billot(Director of INRA Gotheron experimentalorchard) for the use of the facilities in theexperimental orchard, Miss L. Ron (INRAVersailles, Documentation service) for her crit-ical review of the manuscript and Mr M. HalnaduFretay and Miss F. Ressayre for their work inthe plot.

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(Accepted 20 June 1989)

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Responseofpeachtreegrowthandcroppingtosoilwater ...l(lurnal ofHorticultural Science (1989)64(5)541-552 Responseofpeachtreegrowthandcroppingtosoilwater...

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