TEMPORAL DYNAMICS OF PLANT COMPETITION IN GENETICALLY DIVERSE WHEAT POPULATIONS IN THE PRESENCE AND ABSENCE OF STRIPE RUST

1. Effects of disease and environment on competitive interactions amon g wheat genotypes were investigated. Five wheat genotypes were grown i n up to six different two-way combinations and as pure stands in two o r three locations during one to three growing seasons in the presence and absence of wheat stripe rust (caused by Puccinia striiformis). 2. Overall yield of the mixtures relative to the means of the monoculture s did not differ among locations and years. However, interactions betw een genotypes were often affected by location and to a lesser degree b y year. Disease significantly affected seed weight and seed number of the two susceptible genotypes in pure stands and in mixtures. Disease also led to changes in competitive interactions between resistant and susceptible genotypes. 3. Competitive interactions among genotypes oft en changed from early in the season (as measured by the number of till ers) to late in the season (as measured by yield per tiller). In a few mixtures negative correlations between early competitive ability (rel ative number of tillers) and components of late competition suggested that intra-genotypic competition might have been stronger than inter-g enotypic competition.