Differential Induction of Grapevine Defenses by Two Strains of Botrytis cinerea

ABSTRACT Even though Botrytis cinerea, the causal agent of gray mold, is a highly variable fungus with strains displaying very different degrees of virulence toward one given host plant species, no study has yet shown any correlation between the lack of aggressiveness of one given strain and its ability to stimulate a defense response from its host. Strains of B. cinerea collected from different host plant species were screened for their pathogenicity on grapevine to select two strains with similar morphological characteristics but different levels of virulence. In grapevine leaves, the less aggressive strain, T4, enhanced the accumulation of many defense products including secondary metabolites and the pathogenesis-related proteins, chitinase and beta-1,3-glucanase. Interestingly, secondary metabolites were formed in cells around a small group of dead cells. When compared with T4, the more aggressive strain, T8, had larger necrotic spots, no secondary metabolite biosynthesis, and accumulations of chitinases and beta-1,3-glucanases that were more delayed, yet only slightly weaker. The culture fluids of both strains mimicked the differential effect of each isolate in stimulating chitinase activity when infiltrated into grapevine leaves.