Twenty-five spring bread wheat (Triticum aestivum L.) cultivars were evaluated for 2 years at Poza Rica, Mexico, for grain yield, aboveground biomass at maturity, harvest index, yield components, and test weight under a natural epidemic of spot blotch (caused by Cochliobolus sativus) with and without fungicide protection. Diseased plot yields were 43.2% lower than fungicide-protected plot yields. Aboveground biomass yield at maturity and harvest index were reduced by 18 and 31.3%, respectively, on blotched plots. The average percent reduction on primary yield components due to the disease was highest for number of grains per m 2 (32.8%), followed by 1,000-grain weight (30.5%), number of grains per spike (24.6%), and number of spikes per m 2 (12%). Test weight was reduced 8.4%. Resistance to Cochliobolus sativus present in cultivars with resistance from Thinopyrum curvifolium or materials derived from Chinese germ plasm increased grain yield. This germ plasm may be a valuable source of genes for spot blotch resistance in T. aestivum.
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A 1995 study studied this question.