Background/context:

Anthracnose, caused by the fungus Colletotrichum gloeosporioides (Cg), is the most serious postharvest disease of many subtropical and tropical fruit crops including avocado, mango and lychee. In Australia for example, approximately 20-25% of avocados displayed for retail sale are reported to be affected by this disease. While postharvest anthracnose is the most serious disease caused by Cg in fruit crops, preharvest diseases incited by the same pathogen (e.g. pepper spot in avocado and lychee, tear stain anthracnose in mango) are increasing in importance.

 Aim:

The project has aimed to compare Cg isolates from preharvest (pepper spot) and postharvest (anthracnose) symptoms on tropical fruit (avocado, lychee and mango) in terms of pathogenicity, molecular diversity and infection of fruit tissue. Disease susceptibility and host defence mechanisms in a range of avocado rootstock and scion combinations were also investigated. Other objectives for the project included inducing host defence responses in avocado and mango fruit using abiotic and biotic elicitors, and studying the infection process of Cg in mango and avocado fruit using strains which produce quiescent infections and/or limited lesions.

Major Outcomes:

DNA fingerprinting studies found that Cg isolates from avocado causing pepper spot and anthracnose belong to one heterogeneous population. However, Cg isolates collected from mango anthracnose were found to be less pathogenic on avocado than Cg isolates from avocado, and on the basis of DNA banding patterns, formed a distinct homogeneous population. This means that the cross-infectivity potential of Cgfrom mango to avocado is low. The infection process of Cg causing pepper spot was not observed to be significantly different fromCg causing quiescent anthracnose infections. 

A strong link between rootstock, fruit mineral nutrient concentrations, antifungal compounds, and anthracnose susceptibility in avocado has been demonstrated by this study. This knowledge has subsequently led to a significant reduction in chemical usage by the avocado industry. The net benefits of the outcomes from this research have been calculated at around $40 million over a 10-year period – a 58-fold return on the Centre’s investment in this project

For more information contact:

Dr Lindy Coates
Department of Primary Industries and Fisheries
Phone: +61 (0)7 3896 9468
Email: Lindy.Coates@dpi.qld.gov.au