Yield Loss to Spot Blotch in Spring Bread Wheat in Warm Nontraditional Wheat Production Areas. Reynaldo L. Villareal, Wheat Improvement Center (CIMMYT), Apartado Postal 6-641, Delegacion Cuauhtemoc, 06600 Mexico, D.F., Mexico. Abdul Mujeeb-Kazi, Lucy I. Gilchrist, and Efren Del Toro, International Maize and Wheat Improvement Center (CIMMYT), Apartado Postal 6-641, Delegacion Cuauhtemoc, 06600 Mexico, D.F., Mexico. Plant Dis. 79:893-897. Accepted for publication 15 May 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0893.

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 m2 (32.8%), followed by 1,000-grain weight (30.5%), number of grains per spike (24.6%), and number of spikes per m2 (12%). Test weight was reduced 8.4%. Resistance to Cochliobolus sativus pres-ent in cultivars with resistance from Thinopyrum curvifolium or materials derived from Chi-nese germ plasm increased grain yield. This germ plasm may be a valuable source of genes for spot blotch resistance in T. aestivum.

Keyword(s): intergeneric hybridization