COMPARATIVE-STUDY OF THE FIRST STAGES OF INFECTION IN SENSITIVE AND RESISTANT BANANA PLANTS WITH CERCOSPORA-FIJIENSIS (MYCOSPHAERELLA-FIFIENSIS), RESPONSIBLE FOR BLACK LEAF STREAK DISEASE

A study of the first infection stages of banana by Cercospora fijiensis was carried out using an experimental host-parasite system including three cultivars, Yangambi km5 (Musa, AAA, Ibota subgroup), Fougamou (Musa, ABB, Pisang awak subgroup), and Grande naine (Musa, AAA, Cavendish subgroup). These cultivars are representative of three host responses to infection: highly resistant (cessation of the infection process after the first streak stage), partially resistant, and susceptible. Observations on the early stages of infection and the chronology of events linked to the host plant (cellular necrosis) and to the parasite (cessation of growth) showed two different interactions in cvs. Fougamou and Yangambi. These observations were confirmed by an ultrastructural study. Partial resistance in cv. Fougamou appeared to be partly linked to a preexistent anti-fungal, plant phenolic component. In the highly resistant cv. Yangambi, an active defense mechanism took place just after penetration of stomata by the fungus.