Pathogenicity of Bipolaris sorokiniana isolates from wheat roots, leaves and grains in Mexico.
Pathogenicity of 27 Bipolaris sorokiniana (Cochliobolus sativus) isolates from roots, leaves and grains of spring wheat, collected at a site in Mexico, showed no clear differences between groups of isolates, based on lesion density after seedling inoculation of the susceptible cultivar Ciano T-79 under controlled conditions. Results were variable when tests were repeated over time or in experiments using a smaller number of isolates. The lesion number per leaf was significantly different depending on the isolate used for inoculation, irrespective of the plant part group. No difference was found between individual isolates when pathogenicity was assessed using a disease severity scale. No cultivar-isolate interaction was observed for lesion density when 12 isolates were tested on six cultivars, but there were some significant differences between cultivars and between isolates. Results obtained confirmed that infection by B. sorokiniana is highly variable, and very sensitive to environmental conditions. In this study no physiological specialization was observed. The fungus appeared as a continuum of isolates differing in aggressiveness. This work was conducted with isolates from a single site, and highlights the need to assess carefully the biological significance of any differences observed among B. sorokiniana isolates.