Genotype mixtures for control of leaf rust of wheat

Abstract

Three-component mixtures of wheat genotypes were evaluated for yield performance and effectiveness of control of wheat leaf rust, caused by Puccinia recondita Rob ex Desm. The studies were conducted in the 1985-86 and 1986-87 production seasons, at three locations in Central and South Texas, areas prone to severe leaf rust epidemics. Individual experiments utilized either winter or spring wheat genotypes with differing combinations of resistance genes, grown both with and without fungicide treatment. Yields of winter wheat mixtures significantly higher than the mean for the component genotypes were obtained in two of five mixture experiments, both with and without fungicide treatment. Yield component analysis revealed that the performance of some genotypes in mixtures varied significantly from their performance in pure stands. Grain volume weights for mixtures were significantly higher than corresponding weighted means for the components in two of five mixture experiments, for both treatments in one experiment, and for the treatment without fungicide in the other. Severities of leaf rust in mixtures were significantly lower than those for the mean of the components in two of five experiments in untreated plots, and for one of the experiments, in fungicide treated plots as well. Areas under the leaf rust disease progress curves for mixtures were significantly lower than corresponding means for the components in untreated comparisons for three of five winter wheat experiments, and for the fungicide treated comparison in one of them. Grain yields of spring wheat mixtures did not differ significantly from the means for their components in any experiment. Volume weights of spring wheat mixtures significantly exceeded the mean for the components in two of four mixture experiments in the absence of fungicide treatment. In one of the four spring wheat experiments, the severity of leaf rust in mixtures which did not receive fungicide treatment was significantly lower than the mean for the components, while in another of these experiments, the level of leaf rust for the mixture was significantly higher than the mean for the component genotypes. The areas under the leaf rust disease progress curves were significantly lower for mixtures than for the component mean in two experiments for the treatment which did not receive fungicide, and significantly higher for the mixture than the component mean for the same treatment in another experiment.