Alfalfa dwarf disease, a viral complex affecting alfalfa crop in … TRUCCO PPT... · 2018-12-20 · Geographical distribution of AAV in Argentina 64 % 64 % Alfalfa mosaic virus (AMV)

Instituto de Patología Vegetal

Centro de Investigaciones

Agropecuarias

Alfalfa dwarf disease, a viral complex

affecting alfalfa crop in Argentina

Trucco, V.M., Bejerman, N., de Breuil, S., Cabrera Mederos, D., Lenardon, S., Giolitti, F.

Main production purposes: green forage, conserved forage and seed production

Direct grazing Rolls Cubes

Pellets Bales Mega bales

Silage Haylage Seed

ALFALFA CROP IN ARGENTINA

An essential component of bovine meat and milk production

It is the forage crop with the largest cultivated area: over 3.2 million hectares in 2017

The most important forage species

ALFALFA DWARF DISEASE – ADD: Symptoms

Generalized chlorosis of the plant Shortened internodes (dwarfism, bushy appearance)

Diseased stem Asymptomatic stem

ALFALFA DWARF DISEASE – ADD: Symptoms

Leaflet deformations

Chlorosis in the ribs

Vein enations of varying size on the abaxial surfaces of leatlet

ALFALFA DWARF DISEASE – ADD: Symptoms

Virus Order Family Genus

Alfalfa mosaic virus (AMV) - Bromoviridae Alfamovirus

Alfalfa dwarf cytorhabdovirus (ADV) Mononegavirales Rhabdoviridae Cytorhabdovirus

Bean leafroll virus (BLRV) - Luteoviridae Luteovirus

Alfalfa enamovirus-1 (AEV-1) - Luteoviridae Enamovirus

Alfalfa leaf curl virus (ALCV) - Geminiviridae Capulavirus

Viruses detected in alfalfa plants

Collectively called Argentine Alfalfa Viruses (AAV)

Before ADD detection, the only viral disease reported was that caused by AMV

Now, there are five known viruses in alfalfa crop, including AMV

Images taken from: http://viralzone.expasy.org/

How widespread is ADD in Argentina

- 169 surveyed alfalfa fields

- 17 provinces were surveyed

ADD has a wide distribution in our country: it was detected in all surveyed provinces

It is highly prevalent in alfalfa crops (with a prevalence of 87.0%)

Notably, the fields where ADD

was not detected correspond to young alfalfa crops (less than one year old)

ADD: geographical distribution in Argentina

Detected Undetected

Geographical distribution of AAV in Argentina

64 %

64 %

100% Alfalfa mosaic virus (AMV)

Bean leafroll virus (BLRV)

Alfalfa enamovirus-1 (AEV-1)

Alfalfa dwarf cytorhabdovirus (ADV) 72 %

Alfalfa leaf curl virus (ALCV) 86%

Except for BLRV in Chaco, all five viruses were detected in at least one of the ADD sampled fields from each surveyed province

Prevalence values ranging from 64 to 100%.

AMV was the only one of the five viruses detected in all ADD-infected alfalfa samples.

AAV are highly prevalent and have a wide geographical distribution

AAV Prevalence

Viruses can spread to an agricultural crop mainly due to the use of infected seeds, the behavior of vectors and the presence of alternative hosts.

Transmission by seeds Transmission by

vectors

Alternative host survey

Source: http://www.pregonagropecuario.com/cat.php?txt=6107

Seed transmission assay

Seed transmission was recorded only for AMV (3.75%)

Seeds from plants infected with the five viruses were sown.

In total: 672 seedlings.

We carried out vector transmission assays of ADD

Black aphids colonizing ADD-infected alfalfa plants were

collected

Transmission tests were carried out with 5 and 10

aphid/healthy plant

ADD transmission by A. craccivora was confirmed at

a rate of 2 and 10 %.

Aphid transmission assay with black aphids (Aphis craccivora)

Black aphids that were colonizing ADD-infected alfalfa plants were collected

Extraction of nucleic acids

Viral detection by molecular methods

VIRAL DETECTION IN BLACK APHIDS COLLECTED FROM ALFALFA FIELD

Single aphids

Group of 10 aphids

All five viruses were detected:

AMV

ADV

ALCV

AEV-1

BLRV

Except for ADV, the other viruses were detected in single, double and even triple infections:

ALCV

BLRV:ALCV

AEV-1:BLRV:ALCV

AMV:BLRV:ALCV

Black aphids are natural carriers of AAV

ADV

Sampling sites of symptomatic weeds.

Dichondra repens with mosaic, calico, leaf deformation and papillae.

Trifolium repens with chlorosis, enations and leaf deformation.

Melilotus spp. with foliar deformation and chlorotic mosaic

Sonchus oleraceus with calico.

Alternative hosts AMV (+)

Trifolium pratense with mild yellowing in leaves.

AMV (+)

AMV (+)

AMV (+)

ADV (+) AEV-1 (+)

This is the first record of:

- Trifolium pratense infected with AMV in Argentina

- Dichondra repens as natural host of AMV worldwide

- Trifolium repens as natural host of ADV and AEV-1 worldwide

AMV (+)

What about seed production

Preliminary assay conducted in Guanacache (San Juan). Selected alfalfa plants are tagged with ribbons.

Asymptomatic alfalfa plants and plants showing symptoms of chlorosis and vein enations were selected.

No significant difference was observed in the average weights of 100 seeds A decrease of up to 38% in seed production was

observed in plants showing chlorosis and enations symptoms

The symptoms affects the number of produced seeds. The affected plants produce a lower number of seeds.

Asymptomatic plants Symptomatic plants7,00

8,00

9,00

10,00

11,00

12,00

13,00

14,00

15,00

16,00

17,00

weig

ht

of

seed

s p

er

pla

nt

(gra

ms)

Total weight of seeds per plant Mean weight of 100 seeds per plant

Asymptomatic plants Symptomatic plants0,200

0,208

0,215

0,223

0,230

Mean

weig

ht

of

100 s

eed

s p

er

pla

nt

(gra

ms)

(n=106)

AMV(0; n=21) AMV(1; n=85)

ALCV(0; n=7) ALCV (1; n=78)

ADV(0; n=33)

AEV-1 (0; n=29)

BLRV(0; n=11) BLRV(1; n=18)

AEV-1 (1; n=4)

ADV(1; n=45)

BLRV(0; n=19)

BLRV(1; n=26)

AEV-1(0; n=15) AEV-1 (1; n=11)

(n=106)

AMV(0; n=21) AMV(1; n=85)

ALCV(0; n=7) ALCV (1; n=78)

ADV(0; n=33)

AEV-1 (0; n=29)

BLRV(0; n=11) BLRV(1; n=18)

AEV-1 (1; n=4)

ADV(1; n=45)

BLRV(0; n=19)

BLRV(1; n=26)

AEV-1(0; n=15) AEV-1 (1; n=11)

Viral detection (%) in symptomatic and asymptomatic samples

AMV BLRV ADV AEV-1 ALCV

Asymptomatic plants 61.8% 60.0% 65.5% 18.2% 72.7%

Symptomatic plants 96.2% 66.0% 58.5% 35.8% 96.2%

Virus presence was related to seed production and presence of symptoms

Classification tree using number of seeds / plant as a dependent variable and presence of viruses (= 1: presence; = 0: absence) as return variables. Principal component analysis. Data from diseased and healthy samples are indicated in red

and green circles, respectively

BUT, which of the viruses have the most important effect on seed production and symptom development?

Classification tree

The effect of AAV in seed production was analyzed.

-5,00 -2,50 0,00 2,50 5,00

PC 1 (31,6%)

-5,00

-2,50

0,00

2,50

5,00

PC

2 (

17

,9%

)Symptomsnum. seeds/plant

AMV

BLRV

ADV

AEV-1

ALCV

Symptomsnum. seeds/plant

AMV

BLRV

ADV

AEV-1

ALCV

Symptomatic plants

Asymptomatic Plants

Principal component analysis

Healthy alfalfa plant

ADD

Co-infection with AMV-ALCV

These plants showed symptoms that resemble those of ADD: - Leaflet deformation - Vein enation - Chlorosis

AMV-ALCV synergism could cause the ADD symptoms

Have you seen these types of symptoms in your country?

Thank for your attention

Verónica M. Trucco Email: [email protected] Tel: +54-0351-4973636/4343

Contact:

“Do not go where the path may lead, go instead where there is no path and leave a trail” R.W. Emerson

Av. 11 de Septiembre 4755 (X5020ICA)

Instituto de Patología Vegetal

Centro de Investigaciones

Agropecuarias