YIELD LOSS TO SPOT BLOTCH IN SPRING BREAD WHEAT IN WARM NONTRADITIONAL WHEAT PRODUCTION AREAS

Twenty-five spring bread wheat (Triticum aestivum L.) cultivars were e valuated for 2 years at Poza Rica, Mexico, for grain yield, abovegroun d biomass at maturity, harvest index, yield components, and test weigh t under a natural epidemic of spot blotch (caused by Cochliobolus sati vus) 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%, resp ectively, on blotched plots. The average percent reduction on primary yield components due to the disease was highest for number of grains p er m(2) (32.8%), followed by 1,000-grain weight (30.5%), number of gra ins per spike (24.6%), and number of spikes per m(2) (12%). Test weigh t was reduced 8.4%. Resistance to Cochliobolus sativus present in cult ivars 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.