White grain of wheat caused by Tiarosporella spp. periodically affects wheat in Queensland and New South Wales and more recently has been problematic for wheat producers in South Australia, most commonly on the Eyre Peninsula.
The fungus survives in cereal residues and is viable for at least two years. Most severe problems are likely with exposure to infected stubble and in seasons when wet springs promote infection, such as occurred in southern regions of WA during the 2013 spring.
There is no evidence that white grain is associated with toxins and therefore affected wheat grain or stubble can be safely grazed by stock. However, fusarium head blight infection can also produce white grains and may have associated toxins.
Affected grain can be white to very light grey 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. Affected grains could be confused with frost affected grain. Affected grains can be more brittle and can break-up during harvest or grain handling.
Green heads on affected plants may show bleaching or grey discolouration of infected spikelets. Not all spikelets will be affected and therefore usually only some grains in a head will be affected. Symptoms on green heads may be confused with frost. As the crop matures, infected heads may show some greyish discolouration but are very difficult to detect without examining the grain.
Stubble symptoms include 'scabby' nodes with black, slightly raised structures on them.
In maturing crops, rubbing out grain close to harvest is the best assessment method to check crops for white grain. White grain affected plants are likely to be unevenly distributed, so check grain from a number of places in each paddock if scouting for disease.
Currently very little is known about the local epidemiology of the pathogen involved and how this might relate to the occurrence of the disease in WA. The first report of the disease in WA was in 2013, however given that it has been detected from several locations it is possible that it has been present for several seasons without causing any problems. The factors thought to contribute to the occurrence of this disease are the presence of inoculum in the region and wet spring weather which favours infection by the fungus.
Currently there are no recommended management options for this disease. There is no current evidence from other parts of Australia that fungicide applications or variety choice affect disease occurrence. If significant levels of white grain are identified in harvest samples it may be possible to adjust harvester settings to reduce the affected grain going into the bin, as white grain is lighter than healthy grain.
Where has it been found?
In 2013, a small number of deliveries had low levels of white grain contamination from the lower Great Southern region between Tambellup, Jerramungup and Albany. In specific testing in 2014 and 2015, infection levels have been almost undetectable and commercial grain deliveries have not been affected.
In other parts of Australia affected seasons are sporadic and related to very favourable spring weather. Crops in the lower great southern, where inoculum is known to be present, are potentially at risk of White Grain being detected in years with cool wet conditions during flowering and grain formation.
The department are collaborating with South Australian researchers to compare understanding of the source and behaviour of the disease in WA environment. In conjunction with CBH, the collection of grain samples will allow the identification of affected areas and allow for collected grains to be compared for the biology of WA isolates to those in other Australian states.
This factsheet, produced by DPIRD is significantly based on information provided by Dr Margaret Evans and Dr Hugh Wallwork of SARDI.