GRAIN growers who suspect the presence of “white grain” in this year’s wheat crops are being encouraged to contribute to research into the mysterious condition.
White grain has emerged over the past two seasons as a new problem in the southern cropping region, resulting in loads of grain being downgraded or rejected.
With support from the GRDC, researchers are investigating the disease and options for prevention and control.
South Australian Research and Development Institute (SARDI) research scientist Margaret Evans said studies into the condition will be enhanced with the assistance of growers who can supply samples of suspected white grain and location details.
“This will help us to not only map the geographical spread of the disease, but will also ensure that we understand which fungal species are causing the problem,” Dr Evans said.
“Although Fusarium head scab, which results in ‘tombstone grain’, is not implicated in causing white grain in southern Australia we do need to be able to demonstrate that this pathogen is not associated with the white grain.”
White grain was first identified in SA and Victoria in harvested grain in 2010 when some deliveries were rejected based on visual assessment. A larger number of loads were rejected during the 2011 harvest.
Dr Evans said wet conditions over the past two seasons almost certainly promoted the high level of infection.
While little is known about the white grain pathogens, current cultivars all appear susceptible to the disease, but some variation may exist and this is being investigated in field trials.
Fungicide trials are also being repeated on SA’s Eyre Peninsula this year. There are no fungicides approved for control of the white grain pathogens.
The white grain fungi survive in infected cereal residues. Although only wheat has shown white grain symptoms in SA, barley residues are known to host the fungi and contribute to inoculum. Laboratory testing is needed for positive identification.
Dr Evans said it was likely that spores of the fungi were dispersed by rain-splash as well as being wind-blown.
“Spore dispersal patterns are unknown and are currently under investigation, with wind spore traps being set up at Buckleboo on Eyre Peninsula.”
Dr Evans said it was important for growers to check a number of heads from different areas in a paddock as infection levels may be very low and still cause rejection of loads. Infected plants are often patchily distributed.
“Usually only some grains in a head will be affected. Severely affected grain is very light grey to white (and sometimes pinched) when compared with normal grain.
"Less severe symptoms can be difficult to detect as infected grains can look similar in size and colour to normal grain. The germ of infected grain is often shrivelled and just a shell.”
Dr Evans said white grains will not germinate and germination may be reduced in affected grains which do not show severe symptoms. This is an important consideration for growers retaining seed for sowing next season. Seed should be tested just prior to sowing.
Dr Evans suggested that where infection in paddocks can be identified by plant symptoms, growers should be selective about which areas of crop they harvest to keep loads below minimum threshold levels at receival.
