The infection process of two pathogenic races of Colletotrichum truncatum on lentil

The infection process of two pathogenic races of Colletotrichum truncatum on lentil during the biotrophic phase was studied using the susceptible lentil cultivar 'Eston' and 'CDC Robin' which has partial resistance to race 1. Isolates of both races successfully invaded the host tissue of both cultivars through direct penetration aided by appressoria. Overall, conidial germination and appressorial formation on detached leaflets of both cultivars were higher for three isolates of the more virulent race 0 than for three isolates of race 1. Higher appressorium formation of race 0 isolates compared with race 1 isolates was observed on detached 'CDC Robin', but not on 'Eston' leaflets. Conidial germination and appressorium formation of race 1 isolates on detached leaflets were greater on 'Eston' than on 'CDC Robin'. These differences in conidial germination and appressorium formation may contribute to higher aggressiveness of race 0 isolates. Penetration success, however, was not associated with race identity and any differences observed were isolate-specific. The size of primary hyphae assessed at 48 and 60 h post-inoculation (hpi) varied among isolates, but again was not associated with race. Comparison of the detached leaflets with a whole plant assay using two of the six isolates revealed differences in development, indicating that the process of leaf detachment may influence fungal development and host response. Overall, there was no clear evidence for differential development of the two races during the biotrophic phase, indicating that events during the critical switch to necrotrophy or thereafter may be more significant for determining race-specific phenotypes.