PSbMV causes downward rolling of the leaf margins in field peas. These symptoms are difficult to recognise under field conditions (Photo: NSW DPI).
Test field pea seed for virus
by Mary Raynes, Industry Development Manager–southern
While the rain in many parts of the NSW and Victorian cropping zone over summer is very welcome, there is a heightened risk of early aphid flights that may spread viruses in young pulse crops.
Under similar conditions in early 2014 aphid numbers built up on summer weeds and pastures, moving into young pulse crops soon after emergence. Several types of aphids are vectors of viral diseases, which can not be treated once infection has occurred.
Growers need to plan for the heightened risk of virus infection and spread in pulse crops this season.
Seed-borne diseases, such as Pea seed-borne mosaic virus (PSbMV) in field pea, represent a particular, high risk situation because infected seed will produce infected plants throughout a crop. Although the plants infected with PSbMV from seed usually die before maturity they provide a ready source of the virus to be spread by aphids from the start of the season.
Susceptibility to seed transmission varies within the field pea varieties. PBA Wharton, grown in South Australia and Victoria, and Yarrum, grown in southern NSW, are resistant to PSbMV, while the other current field pea varieties are all susceptible to different degrees.
The outcome of sowing seed with different levels of virus infection can vary greatly from year to year and site to site. Testing field pea seed for seed-borne viruses and discarding seed lots with unacceptable infection levels will reduce virus incidences in the crop, particularly in the early stages of crop development.
According to Joop van Leur, Plant Pathologist, Tamworth Agricultural Institute, NSW Department of Primary Industries, crops sown with virus infected seed also become a threat to neighbouring paddocks. For example, the Australian PSbMV strains are not seed-transmitted in faba bean or lentil, but these crops are highly susceptible to the virus. PSbMV can cause severe seed staining in faba bean that leads to down grading of the harvest.
Early virus infections in the 2014 season increased the risk of virus-infected seed being present at harvest and potentially retained for sowing. Even low levels of virus-infected seed can have devastating results under conditions that favour aphid movement, particularly early in the season.
Mr van Leur said that tests done at the Tamworth Agricultural Institute on pea seed lots harvested in 2014 showed unusually high levels of PSbMV infection, confirming that the 2014 season was particularly favourable for virus infection.
Plants infected during the season will produce seed that, depending on the time of infection, can be virus-infected, keeping the cycle of infection going from season to season. Seed samples with even a small percentage of infected seed are considered high risk for PSbMV in field pea.
To minimise losses follow an Integrated Disease Management Strategy that begins with using seed that has been tested for PSbMV, and shown to be safe, or sowing a variety resistant to PSbMV seed transmission. Other strategies that reduce the risk of aphids spreading viruses are sowing into stubble within the recommended sowing window at high seeding rates to promote early canopy development, isolating the crop from legume pastures and controlling weeds that host aphids.
Two laboratories currently offer PSbMV screening services in Australia: AGWEST Plant Laboratories (08 9368 3721) and TASAG Elisa Testing Services (03 6233 6845).
Contact the laboratory for sampling procedures, including their analysis request form. Samples must be representative and graded. Testing for PSbMV costs approximately $550–600 per sample and takes about three weeks.
Input from NSW Primary Industries is gratefully acknowledged.