Virus-induced changes in the response of faba bean to infection by Botrytis

Prior infection of faba bean with the viruses bean yellow mosaic and bean leaf roll increased host susceptibility to subsequent infection by Botrytis fabae and B. cinerea. Cell necrosis beneath inoculum droplets, rate and extent of lesion spread and sporulation of B. fabae were all increased on detached leaves from virus-infected compared with healthy plants. Changes were most marked in young leaves showing conspicuous symptoms of systemic virus infection and in plants virus-infected for at least 2-4 weeks. Localized lesions produced by B. cinerea or a low concentration of B. fabae conidia (10³ spores/ ml) showed increased cell necrosis but were not transformed into aggressive, spreading lesions on virus-infected leaves.