Phytoparasitica (1998) 26 (4) - Mechanisms of defense of ...

D. Prusky, Ilana Kobiler, R. Ardi, D. Beno-Moalem and N. Yakoby (1998)
Mechanisms of defense of unripe avocado fruits against Colletotrichum gloeosporioides attack
Phytoparasitica 26 (4)
International Workshop on Host Specificity, Pathology and Host-Pathogen Interaction of Colletotrichum, August 29 - September 1, 1998, Jerusalem, Israel
Abstract: Colletotrichum gloeosporioides is the most destructive postharvest pathogen of avocado and other tropical fruits. The pathogen infects tropical fruits throughout the period of fruit growth, but remains quiescent for weeks or months while the fruit is immature. Upon harvest and fruit ripening, quiescent infections are activated, causing extensive damage to the fruit. Quiescent infection appears to be a fungal response to adverse physiological conditions temporarily imposed by the host. The quiescence of C. gloeosporioides in unripe avocado fruit has been attributed to the presence of high concentrations of several preformed antifungal compounds, the most active of them being 1-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15-diene. Concentrations of the antifungal diene and epicatechin decrease during fruit ripening and were suggested accordingly as major factors in permitting activation of quiescent infections. The catabolism of the diene after harvest is attributed to the oxidation by lipoxygenase, the activity of which is in turn regulated by epicatechin, a nonspecific inhibitor present in the pericarp of unripe fruits but not ripe fruits. Levels of epicatechin are a critical parameter regulating the mechanism of resistance. Induction of epicatechin level enhances the level of the antifungal diene by preventing its breakdown. Induced levels of epicatechin occur by activation of the phenylpropanoid pathway with enhanced activity of phenylalanine ammonia lyase, chalcone synthase and flavanone-3-hydroxylase. The initiation of the elicitation process has been found recently to occur via the activation of NADPH-dependent oxidase in fruit pericarp. Inhibition of pathogenicity factors, i.e., secretion of pectate lyase, is another possibility for restriction of fungal colonization of host fruits. Fruit pH seems to regulate the secretion of the enzyme and the initiation of fungal colonization of the infected tissue. The general understanding of the plant mechanism that leads to the development of quiescent infection is of primary importance for the manipulation of resistance and can ultimately constitute the basis for novel crop protection strategies.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Database assignments for author(s): Dov Prusky

Research topic(s) for pests/diseases/weeds:
resistance/tolerance/defence of host

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Colletotrichum gloeosporioides	Avocado (Persea americana)