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Relationship Among Seed Size, Planting Date, and Common Root Rot in Hard Red Winter Wheat

A dryland field study was conducted to determine the effect of seed size and planting date of hard red winter wheat on the severity of common root rot caused by Bipolaris sorokiniana (Sacc.) Shoemaker. Seed of cvs. Hawk, TAM 200, TAM 107, Scout 66, and Siouxland 89 were separated into three size categories of small, mixed, and large and were planted in the first weeks of September and October 1994 and 1995. Disease ratings for incidence and severity of subcrown internode infections were made in March and at harvest. At harvest, grain yields were collected. In both years of the study, there was no interaction between seed size and cultivars for any of the measured variables. Overall, seed size had no effect on disease severity or grain yield for either year. However, when sorted by planting date, plants from small seed yielded less than plants from other seed. October plantings showed lower disease indices than September plantings at the March evaluation. At the harvest disease evaluation, there were no differences in disease severity between planting dates for the first year but, in the second year of the study, plants from the October planting had lower disease than those from the September planting. There was no significant correlation among seed size, final yield, and disease index. The results of this study suggest that the expense of planting higher-quality certified seed cannot be justified for producing hard red winter wheat in dryland conditions in the Texas Panhandle, considering the current price of wheat and the average dryland yield.