EXAMINATION OF COMMERCIAL GRAIN SAMPLES TO ASCERTAIN HOW DEOXYNIVALENOL CONTAMINATION EXCEEDED ANTICIPATED LEVELS IN SOME 2014 WHEAT CROPS FROM WESTERN KENTUCKY

摘要

Fusarium head blight (FHB or scab) re-emerged in the USA over two decades ago, first appearing in the Upper Midwest states of Minnesota and North Dakota in 1993. Since that time, FHB epidemics and associated mycotoxin contamination, especially by deoxynivalenol (DON), have been reported in all classes of wheat and in all production regions except the Pacific Northwest. The principal strategy to manage FHB has been the development of wheat varieties with moderate resistance and varieties with improvedresistance to FHB are now deployed in all FHB-prone production regions in the USA. Effective fungicides are also available following a national effort to test the efficacy of fungicides to control FHB. In addition to the multi-state uniform fungicide testing program, effective technologies for the application of fungicides to the wheat head have been developed and deployed. Thus, growers do now have viable options for chemical control. A national forecasting system, The Fusarium Risk Assessment Tool, was developed, and has been deployed in many states for over a decade, to aid growers in deciding if conditions are favorable for FHB development and thus if fungicide applications are warranted. Best management practices recommend that growers combine the best available genetic resistance with a fungicide when conditions are favorable for FHB development. In some instances however, it seems that despite using best management practices, grain is still occasionally contaminated with Fusar ium-mycotoxins.In 2014, a number of soft red winter wheat crops in western Kentucky were rejected because of DON contamination. This appeared to have occurred when the forecasting model had suggested that the risk of FHB development was moderate or low and/or where fungicides had been used and were anticipated to be effective. To better understand the level of mycotoxin contamination of crops in this region, samples from 21 commercial fields, representative of crops in this region, were collected and examined. These samples were evaluated for visual damage to the grain and subsequently tested for the presence of Fusarium-mycotoxins. The percent of visually scabby kernels (VSK), determined by visually matching the 21 grain samples to check samples, ranged from one tothirty percent. The percent of symptomatic kernels, in the samples by weight, ranged from three to thirty three percent. In addition to visual inspections of the grain, 100 seeds from each sample (50 symptomatic and 50 non-symptomatic seeds) were platedon a semi-selective growth media to assess the level of F. graminearum infestation. In one sample F. graminearum was isolated from 86% of the seeds identified as symptomatic and from 70% of the seeds that appeared to be sound. By contrast in another grain sample, F. graminearum was only isolated from 18% of the seeds identified as symptomatic and from 6% of the seeds that appeared sound.