IRON-CHELATING AGENTS AND LESION DEVELOPMENT BY BOTRYTIS-CINEREA ON LEAVES OF VICIA-FABA

B. cinerea produced lesions on leaves of V. faba more rapidly and many more spreading lesions developed when inocula contained the Fe chelating agents EDTA or DHBA [2,3-dihydroxybenzoic acid] than when conidia were inocualted in water alone. Treatment of conidia with EDTA for 3 h prior to inoculation also resulted in increased lesion development. Fe-EDTA or Fe-DHBA in inoculum drops reduced lesion formation to a very low level and no spreading lesions developed. EDTA and DHBA had little effect on germination of conidia on glass slides but were slightly stimulatory to appressoria formation. Fe-EDTA and Fe-DHBA reduced the percentage germination to below 5% and no appressoria were produced. At the leaf surface, however, both germination and appressoria formation were stimulated by EDTA and DHBA whereas Fe-EDTA and Fe-DHBA reduced the percentage germination and appressoria formation when compared with the water controls. Phytoalexins accumulated in the restricted lesions caused by B. cinerea in water but only low levels accumulated in the spreading lesions caused by B. cinerea in EDTA or DHBA solution and at the site of inoculation with conidia in Fe-EDTA or Fe-DHBA solution which remained symptomless. The importance of Fe in the aggressiveness of B. cinerea infecting V. faba, and of 2 other [fungal] pathogens on their host, is discussed.