IDENTIFICATION OF AN ANTIFUNGAL COMPOUND IN UNRIPE AVOCADO FRUITS AND ITS POSSIBLE INVOLVEMENT IN THE QUIESCENT INFECTIONS OF COLLETOTRICHUM-GLOEOSPORIOIDES

A new antifungal compound was isolated from peel and flesh of unripe avocado fruits and identified as 1-acetoxy-2,4-dihydroxy-n-heptadeca-16-ene. The maximal concentration of the anti-fungal monoene in unripe fruits was about 800-mu-g.g-1 fr.wt. During ripening the monoene decreased to 40-mu-g . g-1 fr.wt., concomitantly with the appearance of disease symptoms. The concentration of the previously described antifungal diene, 1-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15-diene (PRUSKY et al. 1982), in avocado peel was 1,600-mu-g . g-1 fr.wt. in unripe fruits, decreasing during ripening to 120-mu-g . g-1 fr.wt. At 750-mu-g . ml-1 the inhibition of germ tube elongation of germinated conidia by the antifungal monoene and the antifungal diene was 15 % and 44 %, respectively. A 1:1 mixture of both antifungal compounds in concentrations ranging from 50 to 750-mu-g . ml-1, showed synergistic activity and increased the percent of inhibited germ tubes of germinated conidia up to 15 % over the sum of activities of the separate compounds. The results are discussed in relation to the hypothesis that the antifungal diene and the antifungal monoene are involved in the quiescence of the germinated appressoria of Colletotrichum gloeosporioides in unripe avocado fruits.