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, p lanted at five frequencies, were grown in three environments in both t he presence and absence of stripe rust. The effect of stripe rust on w heat 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 corre lations among the yield components. Path analysis of the yield compone nts revealed that components with the highest correlations to yield al so had the largest direct effects on yield. Of the yield components, n umber of heads per unit area exerted the largest direct influence on y ield. The direct effects of number of seeds per head and weight of ind ividual 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 coeffi cients, but were very similar for direct effects of yield components o n yield. Most of these discrepancies were due to opposing indirect eff ects, which were not evident from correlation coefficients alone.