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Yield Loss Caused by Bacterial Streak in Winter Wheat

The relationship between severity of bacterial streak and yield in winter wheat was studied in field plots and using a single-tiller method. Regression analysis from single-tiller studies showed that the grain weight per spike decreased as bacterial streak severity increased in cvs. Florida 304 and Savannah. The number of kernels per spike decreased as bacterial streak severity increased in Savannah but not in Florida 304. There was no difference in slope of the regression line between different years, locations, or cultivars for grain weight per spike. However, grain weight per spike at 0% bacterial streak (intercept) was different for different years, locations, and cultivars. The average reduction in grain weight per spike was 0.012 g for every 1% increase in bacterial streak severity. Using this relationship for cv. Savannah, average bacterial streak severity of 10% would result in about a 9% reduction in the grain weight per spike. In Florida 304, bacterial streak severity of 10% would result in about a 7% reduction in the grain weight per spike. During 1993-94, the largest difference in bacterial streak severity between inoculated and noninoculated plots was 4% in cv. Pioneer 2548, and the smallest difference was less than 1% in cvs. Terral 101 and Florida 304. There were no yield differences between inoculated and noninoculated treatments for any genotype. In field plot studies at two locations during 1989-90, bacterial streak severity did not differ between inoculated and noninoculated plots in Alexandria, Louisiana; but in Winnsboro, Louisiana, bacterial streak severity was 18 to 40% in inoculated plots and less than 5% in noninoculated plots. Differences in yield between inoculated and noninoculated plots ranged from 1,370 kg/ha (24% loss) to -121 kg/ha in Winns-boro. During the three seasons in which these studies were conducted, bacterial streak severity averaged about 10% or less in susceptible cultivars in all experiments except one. Based on the relationships derived from single-tiller studies, this suggests that yield loss is likely to be low most years. As indicated by the experiment in Winnsboro, however, more severe yield reductions could occur in a susceptible cultivar if weather conditions are favorable for disease development.