Virulence diversity of anthracnose pathogens (Colletotrichum acutatum and C. gloeosporioides complexes) on eight olive cultivars commonly grown in Portugal.

Abstract

Olive anthracnose, caused by Colletotrichum acutatum and C. gloeosporioides species complexes, is a major disease affecting fruits at maturity, causing significant yield losses, and poor fruit and oil quality. Diverse genetic groups, particularly belonging to C. acutatum s.l. have been reported among the pathogens, with recent research proposing these genetic groups as distinct species. In this work, the virulence diversity of isolates representing different populations of C. acutatum s.l. and C. gloeosporioides s.s. was studied using a set of eight olive cultivars. Higher disease severity was produced by isolates belonging to groups A2 and A5 of C. acutatum s.l. (=C. nymphaeae and C. acutatum s.s., respectively) compared to C. gloeosporioides s.s. isolates as well as isolates of C. acutatum s.l. group A4 (=C. godetiae). Anthracnose severity was higher on the cultivars ‘Cobrançosa’, ‘Maçanilha de Tavira’ and ‘Galega Vulgar’ and lower in ‘Azeitoneira’, ‘Blanqueta’, ‘Negrinha de Freixo’ and ‘Picual’, but results indicate the occurrence of isolate × cultivar interactions. Differences in severity could be related to differences in conidia germination and appressoria formation, suggesting that early host-pathogen recognition events can in part explain disease severity under favourable environmental conditions. Overall results revealed the higher virulence and fitness levels of genotypes belonging to certain genetic groups within C. acutatum suggesting their ability to adapt to diverse agro-climatic conditions including specific hosts.