Suppression of avocado anthracnose and stem-end rot pathogens by endogenous antifungal substances and a surface inhabiting Pestalotiopsis sp.
Adikaram, N. K. B.; Karunaratne, A.;
ACIAR Proceedings Series Year: 1998 Issue: No. 80 Pages: 72-77 Ref: 14 ref.
1998
บทคัดย่อ
Anthracnose (Colletotrichum gloeosporioides [Glomerella cingulata]) and stem-end rot (Phoma spp., Botryodiplodia theobromae and Phomopsis spp.) are recognised as major postharvest diseases in avocado fruit. The former originates from quiescent infections in the immature fruit long before harvest. When isolation of G. cingulata from immature fruit skins was attempted, a surface inhabiting fungus, Pestalotiopsis neglecta, which apparently suppressed the growth of G. cingulata, was often encountered. The resistance of immature avocados to anthracnose is attributed to endogenous antifungal substances in the fruit peel. Two preformed antifungal compounds have previously been reported in Israel. Three more antifungal compounds from immature avocado peel have now been characterised: 1,2,4-trihydroxyheptadec-16-ene (1); 1,2,4-trihydroxyheptadec-16-ene (2); and 1-acetoxy-2,4-dihydroxyheptadec-16-ene (3). These 5 compounds appear to constitute the total antifungal activity of the fruit peel. The most acti
ve compound against G. cingulata was the diene which was twice as active as the monoene and compound (3). The additive effect of all 5 compounds was determined to be equivalent to about 3 times the antifungal activity of diene alone, particularly at the time of harvest. There was a gradual increase in concentration of the 5 compounds in the peel with increasing fruit maturity, and was highest when the fruit were ready for harvest. In the harvested and stored fruits the concentration declined during ripening, coinciding with the onset of anthracnose lesions. P. neglecta, a non-pathogenic, surface inhabitant most commonly encountered on the avocado fruit surface, exhibited strong antagonistic properties in vitro against the major stem-end rot pathogen, Phoma spp. Application of conidia of P. neglecta on to the stem-end region of harvested avocados preinoculated with Phoma sp. delayed stem-end symptom development by 4 days compared with the control. A similar effect was not observed with B. theobromae. In vitro
testing confirmed that P. neglecta was antagonistic to Phoma sp. The antagonism appears to be due to a heat-labile extracellular factor. Dipping avocado fruit in a suspension of conidia of P. neglecta delayed anthracnose and stem-end rot development.