Pathogenicity of monosporic and polysporic Bipolaris sorokiniana isolates to wheat seed and seedling under controlled conditions

Bipolaris sorokiniana may present considerable genetic diversity and highly variable pathogenicity and virulence. The pathogenicity of 99 B. sorokiniana isolates (27 polysporic and 72 monosporic isolates) from Brazil and other countries was assessed. Based on aborted germination, black point of seed, leaf spot, and coleoptile lesion, the principal component analysis (PCA) was used to evaluate the similarity patterns between isolates considering the variables of pathogenicity. Polysporic isolates presented higher virulence (over 60%), when compared with the monosporic isolates (43%) for all variables, except coleoptile injury. Of all isolates used to infect seeds, 8% were highly virulent, and the score obtained was over 75%, for all variables analyzed. The correlation of B. sorokiniana isolates with pathogenicity variables demonstrated that polysporic isolates were more virulent, especially upon seeds, as compared to aerial plant parts. Key words: Variability, virulence, Triticum aestivum L., spot blotch.