Competition BetweenPyrenophora tritici-repentisandSeptoria nodorumin the Wheat Leaf as Measured with de Wit Replacement Series

Abstract

Competitive interactions between Pyrenophora tritici-repentis and Septoria nodorum were studied quantitatively by a modified plant ecology technique known as "de Wit replacement series." P. tritici-repentis and S. nodorum were inoculated alone and in various proportions together on wheat plants [Triticum aestivum] at anthesis. Mature leaves were harvested and incubated in moist chambers, after which fungal porocarps were counted. For each inoculation mixture, the relative yield of each fungus (ratio of its sporocarp yield in the mixed inoculation to its sporocarp yield in single inoculation) was plotted against the proportion of the fungus in the inoculation mixture. The relationship between inoculation ratios and relative yields was compared statistically to a hypothetical noncompetition model. Measurable competition occurred between P. tritici-repentis and S. nodorum. P. tritici-repentis was the better competitor because its relative yields were less affected by the presence of S. nodorum than vice-versa. The de Wit replacement series is a useful tool for quantitatively examining competitive interactions between plant pathogens.