In 2017 researchers requested the industry to submit field pea samples infected with bacterial blight from all pea growing regions around Australia to help understand the prevalence of the pathovars within the pathogen population.
Bacterial blight disease in field peas is caused by the bacterial pathogen, Pseudomonas syringae pathovars syringae and pisi. Several races have been identified in the pisi pathovar, however there is no race specificity in the syringae pathovar. The national field pea breeding program actively breeds for resistance against both pathovars.
A total of 20 samples were analysed and processed for the isolation of bacteria. This was followed with a molecular analysis to differentiate the different pathovars. The sampling variety, location and bacterium identity is presented in the table below. All the confirmed bacterial samples in 2017 were confirmed as syringae pathovar.
|3BB17||Gunyah||Beulah – Vic||no Pseudomonas identified|
|4BB17||Oura||Horsham – Vic||syringae|
|5BB17||Twilight||Deniliquin - NSW||no Pseudomonas identified|
|6BB17||Oura||Beulah - Vic||syringae|
|7BB17||Wharton||Horsham – Vic||syringae|
|8BB17||Wharton||Bordertown – SA||no Pseudomonas identified|
|9BB17||Percy||Beulah – Vic||syringae|
|10BB17||Pearl||Warracknabeal – Vic||syringae|
|11BB17||Oura||Rainbow – Vic||no Pseudomonas identified|
|12BB17||Percy||Rainbow – Vic||syringae|
|13BB17||Butler||Tarranyurk – Vic||no Pseudomonas identified|
|14BB17||Percy||Tarranyurk – Vic||syringae|
|15BB17||Strurt||Sea Lake – Vic||syringae|
|16BB17||Kaspa||Horsham – Vic||syringae|
|19BB17||Twilight + Hayman||Glasshouse re-isolate||syringae|
|20BB17||Race 6||Reisolation of #28 from glasshouse||Pisi Race 6|
The main varieties from where the bacteria were isolated were PBA Wharton, PBA Twilight and PBA Gunyah, all of which are susceptible to this disease. However, it was also found that the early and multiple frost events of 2017 facilitated the expression of disease in more resistant varieties such as PBA Percy and PBA Oura. Historically, the pisi pathovar was the main causal pathogen in conventional type peas, however since the release of semi leafless type pea varieties such as PBA Kaspa and PBA Twilight there appears to have been a shift in the pathogen population to the syringae pathovar. The PBA field pea breeding program has more recently released varieties with good levels of resistance to the syringae pathovar. Both PBA Oura and PBA Butler are rated as MRMS to this disease, however, PBA Butler appears to have higher levels of resistance against the syringae pathovar. Breeding efforts are continuing in the development of robust resistance to this disease.
What can be done
Bacteria blight can present asymptomatically on the plant surface and requires entry into the plant cells through physical damage triggered by frost, chemical sprays, hail etc. Once the pathogen has entered the plant it causes symptoms of water soaked lesions, followed by dried fan shaped necrosis on stipules and the stem (see image). Being a bacterial disease, fungicide sprays will not control the disease but there are management options that reduce the spread of bacterial blight within the diseased paddock. Hygiene practices such as restricted access, avoiding human or machinery contact, which will prevent the disease spread through tyres or boots. Infected crops should be the last pea crop to be harvested to avoid contamination of grain via the harvester and stubble should be destroyed by baling, burying or burning. Infected grain should not be kept for sowing.
Dr Pragya Kant, Agriculture Victoria
Phone: 03 4344 3318, Mobile: 0418 749 984
For more information on submitting samples please read the GRDC Communities – Field Crop Diseases article, Bacterial blight survey to inform breeding efforts
For further information on Bacterial blight symptoms and management read the GRDC Communities – Field Crop Diseases article, Bacterial blight in field peas
For further information on variety selection and disease ratings: Victorian Pulse Disease Guide 2018
Garry Rosewarne, Agriculture Victoria
Jennry Davidson, SARDI