The Effect Of Hot-Water Treatment On The Levels Of Antifungal Diene And Quiescence Of Colletotrichum-Gloeosporioides In Avocado Fruits

Quantitative changes in the antifungal compound 1-acetoxy-2-hydroxy-4-Oxo-heneicosa-12,15-diene in harvested avocado fruits, and the development of symptoms caused by Colletotrichum gloeosporioides, were investigated following treatment with hot water at 55-degrees-C for 10 min. The concentration of the compound in the peel and fresh was 2000 and 2600 mug/g fresh weight, respectively, at the time of harvest, but decreased rapidly during the first 24 h. Levels of the diene had substantially recovered after 50 h. However antifungal diene levels in the peel of hot-water-treated fruit did not recover until 98 h. The levels in the flesh were unaffected by the treatment. Following inoculation, hot-water-treated fruits developed clear symptoms after 2 days, whereas untreated fruits showed only minor symptoms after 6 days. If inoculation was delayed by 24, 48 or 72 h after treatment, then symptoms on treated fruits did not develop until the sixth day as observed for untreated fruits. The correlation between the two systems suggests that quiescence is probably maintained by the level of antifungal diene present in the peel at the time of fungal penetration and the formation of a subcuticular hypha.