Host by pathogen interactions of six Botrytis spp. causing chocolate spot disease on faba bean (Vicia faba L.)

Chocolate spot (CS) disease, caused by Botrytis species, severely damages faba beans. This study analyzed interactions between three faba bean genotypes with varying levels of resistance and 21 Botrytis isolates from six species that were genotyped using 10 NEP markers. The isolates were cultured, sporulated under near-UV light, and inoculated onto 6–8-week-old, fully expanded, detached leaflets. All isolates induced CS symptoms, revealing significant interactions among lines and isolates. Botrytis fabae 19B053-4 was the most virulent, followed by B. fabiopsis 19B175 and B. fabae 17B4. Conversely, B. cinerea 17B10-1 caused the slowest lesion development. Notably, more resistant hosts consistently remained less susceptible across all isolates, indicating no crossover interaction. AUDPC values confirmed B. fabae as the primary, highly aggressive specialized pathogen, whereas related species pose opportunistic threats. Tracking cumulative disease progress identified quantitative host resistance through slowed infection rates, offering a framework for crop protection.