Function of Host and Fungal Metabolites in Resistance Response of Banana and Plantain in the Black Sigatoka Disease Pathosystem (Musa spp. –Mycosphaerella fijiensis)

The host pathogen interactions of Musa spp[ and Myco! sphaerella _jiensis were investigated in order to determine the function of secondary metabolites within the patho! system of the Black Sigatoka disease[ The pentaketide metabolites ~aviolin\ 1!hydroxyjuglone\ juglone and 1\3\7!trihydroxytetralone "1\3\7!THT# of the pathogen were identi_ed[ The concentration of 1\3\7!THT was sig! ni_cantly increased by application of the synthetic com! pound tricyclazole and by natural activators extracted from the intercellular space of leaf tissue of resistant Musa cultivars[ When inoculated host plants were treated with tricyclazole\ extensive necrosis of both susceptible and resistant Musa cultivar leaves were observed[ Plant defence mechanisms of resistant Musa cultivars were _rst detected as an activation of phenylalanine ammonia lyase and the subsequent accumulation of post!infec! tional substances which blocked fungal growth[ These results indicated the bivalent importance of 1\3\7!THT for host!speci_c reactions\ depending on its con! centration at di}erent stages of pathogenesis[ Early acti! vation of fungal 1\3\7!THT metabolism by resistant Musa cultivars caused necrotic micro!lesions and elicitation of post!infectional defence reactions leading to incom! patibility between pathogen and host plant^ growth of the fungus on susceptible cultivars caused necrotizing doses of 1\3\7!THT only after the establishment of a compatible interaction and development of typical symp! toms at late stages of pathogenesis