Iron-dependent, non-enzymatic processes promoted by Phaeomoniella chlamydospora and Phaeoacremonium aleophilum, agents of esca in grapevine

Esca is a serious disease, caused mainly by two vascular fungi, Phaeomoniella chlamydospora and Phaeoacremonium aleophilum, in a complex infective process that has not yet been fully elucidated. The cellulose-degrading system of these two fungi was examined and was found to be unable to degrade crystalline cellulose. When iron was added to the culture medium, however, Pa. chlamydospora and Pm. aleophilum were able to degrade crystalline cellulose: the iron formed hydroxyl radicals that made up for the lack of specific enzyme activity of the fungi. The iron did not affect the activity of the other enzymes present, such as the endoglucanases. It is shown that iron-dependent processes of a non-enzymatic nature occur, and that these amplify the pathogenic capacity of Pa. chlamydospora and Pm. aleophilum, supplementing the pathogenic capacity of the enzymes. The manner in which these non-enzymatic processes can help to further our understanding of the nature of interaction between grapevine and the esca pathogens is discussed.