Assessment of Losses on Spring Wheat Naturally Infected with Barley Yellow Dwarf Virus. C. C. Gill, Research Scientist, Agriculture Canada, Research Station, 195 Dafoe Road, Winnipeg, Manitoba, R3T 2M9, Canada. Plant Dis. 64:197-203. Accepted for publication 17 September 1979. Copyright 1980 American Phytopathological Society. DOI: 10.1094/PD-64-197.

An outbreak of barley yellow dwarf in southern Manitoba in 1978 provided an opportunity to study the epidemiology of the disease and to determine losses on wheat (Triticum aestivum L.). Sampling of plants with or without the disease in growers' fields revealed 73 and 69% losses in total seed weight per plant of cultivars Glenlea and Neepawa, respectively. The total estimated losses from the disease on bread wheat, calculated for the nine Crop Reporting Districts affected by the epidemic, was 159,260 t (5,851,000 bu) or 7% of the potential yield. Regression analysis of the results with Neepawa indicated a high degree of correlation between yield and the intensity of the disease (r = –0.97). Size distribution and most of the milling properties of Glenlea and Neepawa seed were affected by the disease. The percent germination and the weight of plants grown from seed were also lower from diseased than from healthy plants. When three wheat cultivars at four stages of growth in the greenhouse were inoculated with an aphid-nonspecific isolate of barley yellow dwarf virus, Glenlea was the most susceptible to seed yield losses, followed by Sinton and then Neepawa. Losses on these cultivars were progressively lower with later inoculations, but with Sinton and Neepawa, losses were higher at the fourth stage of inoculation (late jointing) than at the third stage (early jointing).