Biochemical screening of chocolate spot disease on faba bean caused by Botrytis fabae

In this work, three faba bean cultivars were studied. The cultivar Giza 429 was the most susceptible cultivar to chocolate spot disease, followed by Giza 40, which was moderately susceptible; cultivar Giza 461 was found to be resistant. Four fungal species associated with diseased leaves were isolated from naturally infected samples and identified as Botrytis fabae, Alternaria alternata and Stemphylium sp. The most frequently isolated fungus was B. fabae, with an average isolation frequency of 51.03%. Of the B. fabae isolates, six were pathogenic in Giza 429 and Giza 40, and the symptoms of chocolate spot appeared three days after inoculation: B. fabae isolate No. 1 was the most virulent, whereas isolate No. 6 was the least virulent. The effect of B. fabae infection in the two varieties caused biochemical changes in the content of phenolics, oxidative enzymes, phytoalexins and free amino acids. HPLC analysis showed that the resistant cultivar Giza 461 demonstrated significantly higher amounts of oxidative enzymes, free, conjugated and total phenols and phytoalexins (wyerone acid, wyerone and wyerone epoxide) compared with the highly susceptible cultivar Giza 429. The results of this study may improve our understanding of the biochemical basis of resistance to B. fabae in the faba bean.