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The hostÐpathogen 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 phenylalanineÐammonia 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[

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Two strains of bacteria, Bacillus subtilis T 99 and Streptomyces sp. G 43, antagonistic t o phytopathogenic soil fungi, were isolated from natural substrates. In vitro tests indicated activities against different Fusarium species including formae speciales of Fusarium oxysporum, Stromatinia gladioli, Botrytis cinerea, Thanatephorus cucumeris, and other fungi. For both of the antagonists, biotechnical procedures were developed yielding culture broth for large-scale application. After dilution of these media antagonists were tested successfully in vivo by soil drenching treatments in a greenhouse carnation production facility. The application forms of the fermentation media developed were capable of suppressing wilt disease of Dianthus.

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