Evaluation of a collection of faba bean (Vicia faba L.) genotypes originating from the Maghreb for resistance to chocolate spot (Botrytis fabae) by assessment in the field and laboratory

Screening of 136 faba bean lines for resistance to chocolate spot caused by the fungus Botrytis fabae was conducted in field conditions with artificial inoculation. Detached leaves of these genotypes were also assessed for disease severity after inoculation under controlled conditions with a B. fabae suspension. The BPL710 and Aguadulce genotypes were inserted as resistant and susceptible checks, respectively. Disease symptoms were scored visually in both experiments. Diameter of lesions and production of spores were measured in the detached leaf assay. The disease score index and diameter of lesions were used to calculate the area under the disease progress curve (AUDPC) to measure the disease progress. Significant differences were detected among genotypes for reaction to the disease in the field. However, no complete resistance was observed. For highly susceptible and highly resistant genotypes, the laboratory assay generally led to the same result as the field test, nevertheless, for more intermediate levels the agreement was weak. On detached leaves, diameter of lesions was significantly correlated to the AUDPC of disease scores (r=0.89) and moderately correlated to sporulation (r=0.52). The correlation between field AUDPC and detached leaf AUDPC of disease scores was low (r=0.26). A low correlation was also observed between field AUDPC and lesion size (r=0.30) and between field AUDPC and sporulation (r=0.32). Among the 136 genotypes evaluated in this study, nine were convincingly and highly resistant in both tests. FRYM167 and FRYA58 genotypes were the most resistant with low AUDPC of disease scores, low AUDPC of lesion diameter and low spore production. These genotypes obviously have partial resistance.