Effects of wheat leaf rust on interactions between wheat and wild oats planted at various densities and proportions

The importance of competition as a major influence on the composition and s tructure of plant communities has recently been questioned, because other t ypes of interactions can cause significant compositional changes. The goal of this research was to broaden our understanding of disease as a process s tructuring plant communities under a variety of competitive scenarios. Two cultivars of spring wheat (Triticum aestivum L., cv. Twin and cv. Penawawa) and wild oats (Avena fatua L.) were planted at three densities and at five proportions. One-half of the experimental material was inoculated with ure dospores of Puccinia recondita. Increasing the proportion of wheat or oats in mixtures led to significant increases in the amount of aboveground bioma ss and total seed weight for that species. The seed weight and aboveground biomass per culm or per planted seed decreased for wheat and wild oats as t he proportion of wild oats increased in mixtures, indicating a competitive advantage for wild oats when grown with wheat. Wild oats generally did not respond significantly to the effects of leaf rust on wheat, while wheat per formance declined. Lowered wheat performance in inoculated stands was the m ain reason for lower relative biomass ratios of wheat to wild oats. Puccini a recondita infections occurred late in the life cycle of wheat, thereby de creasing the potential impact on wild oats' adults through competitive inte ractions.