Deceptive behaviour of Colletotrichum truncatum: Strategic survival as an asymptomatic endophyte on non-host species

Abstract

Colletotrichum truncatum (syn. C. capsici), like many other members of the genus Colletotrichum, displays a highly developed infection mechanism against a number of agriculturally important crops. Among many survival strategies, C. truncatum is well known for its wide host range and high pathogenicity on several major crop species. Meticulous understanding of a pathogen's infection mechanisms is the best way to achieve successful management of a disease. This study was carried out to evaluate the pathogenicity of C. truncatum on selected crop plants and weed species and to detect the possibility of non-host species to facilitate survival of the pathogen. Inoculation of an isolate of C. truncatum to four crops: curry chilli - Capsicum annuum (var. CA8), eggplant - Solanum melongena (var. Lena Iri), tomato - Solanum lycopersicum (var. Thilina) and green chilli - C. annuum (var. KA2) and three weed species: little ironweed (Vernonia cinerea), billygoat-weed (Ageratum conyzoides) and Bengal dayflower (Commelina benghalensis) resulted in approximately 3.5 disease severity (DS) (100% disease incidence-DI) on S. lycopersicum and C. annuum (var. KA2), followed by 2.8 and 1.8 DS (100%, 75% DI) on C. annuum (var. CA8) and S. melongena (var. Lena Iri), respectively. The three weed species were completely symptomless up to 8 weeks after the inoculation (WAI). However, microscopic studies and serial culturing of the inoculated tissues revealed the presence of the fungus in all the tested plants. Appressoria were present in all treated leaves and eventually broke their dormancy upon leaf senescence nearly 6 WAI. This study reveals the potential of C. truncatum infecting all tested crops and the capability of the three weed species in harboring the pathogen asymptomatically for several weeks. Thus, early management of inoculum in the field is suggested for C. truncatum diseases.