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Temperate Pulse Viruses: Beet Western Yellows Virus (BWYV)

Note Number: AG1419
Published: July 2010
Updated: April 2013

Mohammad Aftab and Angela Freeman, Virologists 

Beet western yellows virus (BWYV) has an extremely wide host range and is distributed worldwide. Hosts include temperate pulses (chickpea, faba bean, lentil, field pea and vetch), pasture legumes (clover, medics and lucerne), canola and many perennial weeds. BWYV is transmitted persistently by a large number of aphid species, but it is not transmitted mechanically or through seed. It persists between crop seasons on alternate hosts such as perennial weeds, lucerne and summer brassicas. Control measures include monitoring and spraying aphids, as well as the eradication of alternate virus reservoirs such as weeds.

What to look for

The general diagnostic symptoms of BWYV in pulses include yellowing, rolling and stiffening of leaves, and stunting. In canola, they include reddening in young plants and ill-thrift in older plants. Symptoms for individual crop, pasture and weed hosts are as follows:

• Kabuli chickpeas develop pale, chlorotic leaves with stunted plants (Figures 1 and 2).
• Desi chickpeas develop purple leaves with mild stunting.
• Lentils develop yellowing on lower and middle leaves, but tips grow out green. Stunting may occur (Figure 3).
• Field peas develop leaf yellowing and stunting.
• Faba beans develop leaf yellowing, tip necrosis and stunting.
• Canola develops reddening of lower leaves, stunting, yellow margins, but can be symptomless.

Symptoms of BWYV in pasture:

• Subterranean clover develops systemic leaf reddening.
• Lucerne is symptomless

Symptoms of BWYV in common weeds of southern Australia:

• Marshmallow develops leaf yellowing, young leaves are cup shaped and reduced in size (Figure 4).
• Bifora develops yellow and purple leaves. Late infection causes no stunting.
• Wild radish leaves develop yellow blotches and stunting.
• Three-horned bedstraw develops reddening of top leaves.
• Prickly sowthistle develops yellowing on lower leaf margins.

Economic importance

In recent years BWYV has emerged as an important virus problem in pulse crops in south eastern states (Victoria, South Australia and New South Wales) (Table 1, page 3).

The virus level has increased in chickpea, lentil and field pea crops since 2007. Chickpea surveys in 2009 in Victoria, New South Wales and South Australia highlight the high incidence of this virus in both Desi and Kabuli crops. The virus and its aphid vectors survive during summer in weeds and pastures such as mustards, turnips and lucerne. Aphids carry the virus into winter pulse crops from these sources.

BWYV is reported in a range of crops worldwide. In oilseed rape in UK, BWYV caused 26 per cent yield loss in field trials (Jay et al. 1999). In Australia, the virus is responsible for yield losses in pulses, canola and vegetable crops. Western Australian researchers found BWYV in 59 per cent of canola crops, while the within crop virus incidence was up to 65 per cent. Subsequent canola yield was reduced 37 per cent (Coutts and Jones 2000).

Disease cycle

Plant viruses are sub-microscopic disease agents. They live inside plant cells, and depend entirely on their host plants for reproduction. Once a plant is infected with a virus it cannot be cured. BWYV persists over summer in weed or summer pasture hosts. The virus is not seed-borne, and is spread from host plants into crops by aphids, which act as the vector for transmission of the virus.

Transmission

BWYV is transmitted by several aphid species in a persistent manner. Persistent viruses are carried in the aphid’s body, and can be transmitted to healthy plants during feeding. The aphids will remain infective throughout their life. In DPI surveys of southern Australia many aphid species were found to transmit BWYV. They include cowpea aphid (Aphis craccivora), foxglove aphid (Aulacorthum solani), cabbage aphid (Brevicoryne brassicae), ornate aphid (Myzus ornatus), green peach aphid (Myzus persicae), lucerne blue green aphid (Acyrthociphon kondoi), sowthistle green aphid (Hyperomyzus lactucae) and spotted alfalfa aphid (Therioaphis trifolii forma maculata).

Host range

The host range of BWYV is very wide, and most temperate pulse crops grown in southern Australia are hosts. Pulse hosts include chickpea, lentil, field pea, faba bean and vetch; pasture legumes like lucerne, clovers and medics; tropical legumes such as French bean and soybean, as well as other field crops like canola, and sunflower. Horticultural crops like crucifers and lettuce, and many common weeds are also infected by the virus. Infected weeds and forage brassicas are of particular importance, as they host BWYV over the summer and in the early autumn.

DPI surveys in Victoria and South Australia identified a number of weed hosts of BWYV such as marshmallow (Malva parviflora), muskweed (Myagrum perfoliatum), wild radish (Raphanus raphinistrum), prickly sow thistle (Sonchus asper), three-horned bedstraw (Galium tricornutum) and bifora (Bifora testiculata).

Management

BWYV is spread by aphids. Perennial weeds, self-sown pulses, canola and forage brassicas can act as a "green bridge" that allows aphids and the virus to survive between seasons. Therefore, weed management and aphid control are important strategies.

Green bridge management

• It is important to manage the green bridge, and eliminate infection sources by controlling host weeds that act as a reserve for aphids and the virus over summer, and between seasons. Management of virus and its vector aphids in forage brassicas in southern Victoria is also important to reduce the likelihood of viruliferous aphids moving into winter pulse crops.

Chemical control

• Consider using a seed-dressing with the insecticide imidacloprid (registered as Gaucho 350® for use in field peas, faba beans and lentils) in years where there has been extensive weed growth over the summer and autumn months. This can prevent the aphid feeding for up to 2 months after crops germinate. Monitor crops, as early aphid control is essential to manage aphid infestations and minimise spread of the virus.

Resistance

• Breeding of pulses for BWYV resistance is being undertaken, but no resistant varieties are currently available.

Cultural

• Aphids are attracted to bare earth, and more virus damage occurs where plant densities are low.
  
• Retaining the previous year’s cereal stubble as ground cover will reduce aphid infestation.
  
• Sow at optimal seeding rate to encourage early canopy closure, and reduce aphid attraction to plants next to bare soil.
• Control in-crop and fallow weeds to remove sources of infection.
• Distance pulse crops from lucerne and forage brassicas, which can act as reservoirs for aphids and viruses.
  
• Given the wide host range of BWYV, consider sowing pulse crops away from canola.
  

Further references

More information can be obtained from the DPI Information Note Series:

DPI Information Series

Victorian Winter Crop Summary

Winter Pulse Disorders: The Ute Guide.

Seed Health Testing in Pulse Crops (AG1250)

Pulse Australia - Virus control in chickpea–special considerations

Pulse Australia Tech-Notes Autumn 2010 - Chickpea "sudden death" in 2009

Detailed information can be obtained from:

Coutts BA and Jones RAC (2000) Australian Journal of Agricultural Research 51, 925-936.

Coutts BA, Hawkes JR and Jones RAC (2006). Australian Journal of Agricultural Research 57, 975-982.

Coutts BA, Webster CG and Jones RAC (2010) Crop and Pasture Science 61, 321-330. 

Jay CN, Rossal S and Smith HG (1999) Journal of Agricultural Science Cambridge 133, 131-139.

Johnstone GR and Duffus JE (1984) Australian Journal of Agricultural Research 35, 821-830

Latham, LJ, Smith LJ and Jones RAC (2003). Australian Journal of Plant Pathology 32, 387-391.

Maling T, Diggle AJ, Thackray DJ, Siddique KHM and Jones RAC (2008) Phytopathology 98, 12: 1280-1290.

Maling T, Diggle AJ, Thanckray DJ, Siddque KHM and Jones RAC (2010) Crop and Pasture Science 61, 132-144.

Contact/Services available from DPI

DPI Field Crops Pathology, Grains Innovation Park, 110 Natimuk Rd, Horsham 3400. Tel (03) 5362 2111, or the DPI Customer Service Centre 136 186.

Acknowledgement

This Information Note (AG1419) was written by Mohammad Aftab and Angela Freeman, Bacteriology & Virology – DPI Horsham. It was reviewed by Frank Henry, Farm Services Victoria, April 2013. Financial support by the GRDC is gratefully acknowledged.

Table 1: Percentage of pulse crops infected with beet western yellows virus in south eastern Australia, and within crop virus incidence 

Virus Survey	Faba bean		Chickpea		Field pea		Lentil
State/Year	% of sampled crops infected	within crop virus incidence   range %	% of sampled crops infected	within crop virus incidence   range %	% of sampled crops infected	within crop virus incidence   range %	% of sampled crops infected	within crop virus incidence   range %
Victoria
2004	0	0	13	1	7	1	0	0
2006 Pea only	*	*	*	*	100	4-28	*	*
2007	67	1-8	100	18-61	100	8-36	88	5-39
2008	*	*	*	*	*	*	*	*
2009 chickpea only	*	*	100	5-69	*	*	*	*
South Australia
2003	9	1	33	1	0	0	0	0
2004	0	0	*	*	16	1-6	7	1
2005	2	1-2	*	*	1	1	1	1
2006	67	2-5	100	3-8	0	0	100	9-36
2007	90	1-57	100	8-25	100	3-79	100	17-73
2009	*	*	58	1-19	*	*	*	*
New South Wales
2006 Southern	33	6	*	*	62	1-63	*	*
2009 Southern	*	*	71	3-58	*	*	*	*
2009 Northern	*	*	73	1-29	*	*	*	*
Note: * = crops not sampled/not tested; 0 = virus not found. In 2008 in Victoria 20 canola crops were sampled, 5 crops were found infected with BWYV within crop infection range was 1-2%.  In 2009, 4 canola crops were also sampled from South Australia, 2 crops were infected and within crop. BWYV infection ranged 11-30%.