Symptoms and Prepenetration Events Associated with the Infection of Common Bean by the Anamorph and Teleomorph ofGlomerella cingulataf.sp.phaseoli

Abstract

Glomerella cingulata f.sp. phaseoli and Colletotrichum lindemuthianum are the teleomorph and anamorph, respectively, of the pathogen causing anthracnose in common bean. The mechanisms relating to the sexual reproduction of this plant pathogen are still unclear, as are the infection structures involved and the symptoms produced. In the present study, bean plants were inoculated with ascospores and conidia, and the events taking place within the following 120 h were investigated using light microscopy and scanning electron microscopy. The symptoms exhibited by plants inoculated with the ascospores were milder than in those inoculated with conidia. Microscopy revealed that most of ascospores produced germ tubes and appressoria at an early stage (24 h after inoculation). From 48 h onwards, the formation of hyphae and the production of germ tubes and appressoria were great. In contrast, infections originating from conidia developed more slowly, and at 24 and 48 h, many non-germinated conidia were present, whereas only few conidia developed germ tubes and appressoria. Ascospore germination and appressorium formation were similar on both resistant and susceptible cultivars. Hence, the symptoms and the temporal sequence of events associated with the infection of bean plants by the two fungal forms differed, although the structures produced were similar. This is the fist report comparing symptoms and prepenetration events between anamorph and teleomorph of G. cingulata f.sp. phaseoli in common bean.