Variation in Virulence and Host Specificity of Pyrenophora tritici-repentis on Common and Durum Wheat in North Dakota, USA and Morocco

Abstract

Differential virulence of Pyrenophora tritici-repentis. (PTR) on durum wheat (Triticum turgidum var. durum Desf.) and bread wheat (T. aestivum L.) may be the first concern in developing a strategy for breeding cultivars resistant to tan spot. The objective of this study was to evaluate the variation in virulence and host specificity in PTR isolates from North Dakota, USA and Morocco. Eleven wheat genotypes were inoculated with nine PTR isolates collected in North Dakota and by eight isolates collected from different regions of Morocco. The experiments were planted in the greenhouse as split-plots, using isolates as main plots and wheat genotypes as subplots. Lesion size on individual leaves was used for disease ratings. Highly significant host genotype, pathogen isolate, and genotype X isolate effects were observed in both experiments. Cluster analysis indicated that differences among clusters of PTR isolates were larger in North Dakota, but more dissimilar patterns were observed in Moroccan isolates. Differences in host genotypes' ranking and disease reaction patterns indicated differences in virulence between the PTR isolates from North Dakota and Morocco.