Ground Cover Supplement : GC Supplement - Cereal foliar fungal diseases
22 Northern region TEST SEED BEFORE JUDGING RESISTANCE RATING "The contaminated seed lots are unfairly tarnishing the resistance rating of Sunvale," Dr Simpfendorfer says. "And this has the potential to jeopardise industry confidence in stripe rust resistance breeding as a whole." Dr Simpfendorfer does not believe the situation is unique to Sunvale and may also possibly explain reports of stripe rust in commercial crops of more recently released MR varieties such as EGA GregoryA. "Testing of seed for purity is critical for correct identification of seed lots before planting." In collaboration with the University of Queensland, Dr Simpfendorfer compared the DNA molecular marker banding patterns of wheat seed from Sunvale commercial seed lots with the unique marker pattern only observed in Sunvale. "What we found surprised us," Dr Simpfendorfer says. Sixteen of the 23 seed lots had at least five per cent contamination with wheat varieties other than Sunvale. Only seven of the 23 seed lots were 95 per cent pure Sunvale. One of the commercial lots was not PHOTO: CHRIS STACEY NSW DPI plant pathologist Dr Steven Simpfendorfer ran purity tests on 23 commercial Sunvale seed lots and found more than 70 per cent were contaminated with wheat varieties susceptible to stripe rust. Sunvale at all -- presumably the result of a silo mix-up either at sowing or harvest. Contaminated seed lots contained between four and 14 different wheat varieties. "Given that Sunvale has been around for nearly two decades it is not surprising that seed lots are starting to show up with contamination," Dr Simpfendorfer says. The molecular marker work was backed-up by field trials at Tamworth, NSW, which rated the disease infection and characterised the head morphology of the 23 seed lots. Less than 10 per cent of the seed lots proved completely pure for Sunvale. Dr Simpfendorfer urges growers to test the purity of seed lots before sowing. "It is important to test seed for purity before passing judgement on the resistance rating of a variety so that industry confidence in disease ratings is not compromised." □ grdc research codes dan00143, usQ00012 more information: Dr Steven Simpfendorfer, NSW DPI, 02 6763 1261, firstname.lastname@example.org contaminated wheat seed lots are compromising disease-rating guides, with growers in the northern region reporting high levels of stripe rust infestations in sunvale crops, despite the variety’s ‘moderately resistant’ disease rating By Janet Paterson REPORTS OF STRIPE rust outbreaks in a popular wheat cultivar thought to be resistant to the disease can be explained by seed contamination rather than a breakdown in resistance genetics. Cereal plant pathologist Dr Steven Simpfendorfer, from the New South Wales Department of Primary Industries, says the stripe rust outbreaks in the widely grown northern region cultivar Sunvale were a case of stolen identity. "We tested the genetics of 23 commercial Sunvale seed lots and discovered that in 70 per cent of cases the lots contained rogue wheat varieties, all of which proved susceptible to moderately susceptible for stripe rust." Dr Simpfendorfer says pure Sunvale remains moderately resistant (MR) to stripe rust and does not require in-crop fungicide management. In 2010, a season highly conducive to the development of fungal leaf diseases, National Variety Trials found Sunvale plots had very low levels of stripe rust development, consistent with the variety's MR rating.
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