Chocolate spot of faba bean ( Vicia faba L.): disease status and pathogen phenotypic variability in Morocco

Chocolate spot disease is a major constraint to faba bean production in Morocco. This study assessed its prevalence and characterised the phenotypic diversity of associated Botrytis spp. to inform disease management. A four-year survey across five key Moroccan regions confirmed the widespread occurrence (100% field prevalence) of chocolate spot in diverse agro-ecological zones. Among 73 isolates characterised, Botrytis fabae (73% of identified isolates) was predominant over Botrytis cinerea (26%). While isolates exhibited considerable morphological diversity, this did not correlate with geographic origin. Pathogenicity assessment of 50 isolates on four differential faba bean varieties revealed three distinct virulence clusters (low, moderate, high). Notably, highly virulent isolates were concentrated in the semiarid Doukkala region, supporting a significant link between pathogen aggressiveness and agro-ecological conditions. Furthermore, faba bean varieties responded differentially and significantly to these virulence clusters (ANOVA, p < .005). These findings highlight the complex nature of Botrytis populations and underscore the critical need for region-specific resistance breeding programs and tailored deployment of faba bean cultivars in Morocco.