J. Phytopathology 132, 319—327 (1991) © 1991 Paul Parey Scientific Publishers, Berlin and Hamburg ISSN 0931-1785 Agricultural Research Organization, The Volcani Genter, Bet Dagan, Israel; and Department of Plant Pathology, University of Galifornia, Riverside, GA, U.S.A. Identification of an Antifungal Compound in Unripe Avocado Fruits and its Possible Involvement in the Quiescent Infections of Colletotrichum gloeosporioides^ D. PRUSKY, I. KoBiLER, Y. FiSHMAN, J. J. SiMs, S. L. MIDLAND and N . T. KEEN Authors' addresses: D. PRUSKY, I. KoBlLER, Y. FISHMAN, Depanment of Fruit and Vegetable Storage, A.R.O., The Volcani Center, P.O. Box 6, Bet Dagan 50250 (Israel). J. J. SiMS, S. L. MIDLAND and N. T. KEEN, Department of Plant Pathology, University of California, Riverside, CA 95251 (U.S.A.). With 3 figures Received October 9, 1990; accepted November 19, 1990 Abstract A new antifungai compound was isolated from peel and flesh of unripe avocado fruits and identified as l-acetoxy-2,4-dihydroxy-n-heptadeca-16-ene. The maximal concentration of the anti- fungal monoene in unripe fruits was about 800 ^g • g"' fr.wt. During ripening the monoene decreased to 40 jUg • g"' fr.wt., concomitantly with the appearance of disease symptoms. The concentration of the previously described antifungal diene, l-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15-diene (PRUSKY et al. 1982), in avocado peel was 1,600 ^g • g~' fr.wt. in unripe fruits, decreasing during ripening to 120 jug • g"^ fr.wt. At 750 fig • ml"' 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 ^g • ml"', 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 antifungai monoene are involved in the quiescence of the germinated appressoria of Colletotrichum gloeosporioides in unripe avocado fruits. ' Contribution from the ARO, No. 3105-E, 1990 series. U.S. Copyright Clearance Center Code Statement: 0931-1785/91/3204-0319$02.50/0