Path coefficient analysis of the effects of stripe rust and cultivar mixtures on yield and yield components of winter wheat.

Four club wheat cultivars and three two-component cultivar mixtures, planted at five frequencies, were grown in three environments in both the presence and absence of stripe rust. The effect of stripe rust on wheat yield was through the yield components, with weight of individual seed being the component most affected by rust. In some cases, yield component compensation was indicated by the presence of negative correlations among the yield components. Path analysis of the yield components revealed that components with the highest correlations to yield also had the largest direct effects on yield. Of the yield components, number of heads per unit area exerted the largest direct influence on yield. The direct effects of number of seeds per head and weight of individual seed were similar, although number of seeds per head was more important in the absence of rust than in its presence. The pure stands and mixtures differed considerably with respect to correlation coefficients, but were very similar for direct effects of yield components on yield. Most of these discrepancies were due to opposing indirect effects, which were not evident from correlation coefficients alone.