Recessive and dominant genes confer resistance to Colletotrichum truncatum in cultivated lentil

Abstract

Anthracnose caused by the fungal pathogen Colletotrichum truncatum is one of the most damaging diseases of lentil in western Canada. Two physiological races, Ct0 and Ct1, exist of this pathogen and lentil accessions have been identified with resistance to one or both races. In this study, the genetics of resistance to race Ct1 was examined in cultivar ‘Indianhead’ (Czechoslovakia) and two plant introductions PI320937 (Germany) and PI345629 (former Soviet Union). Segregating populations were generated from crosses between each resistant line and a susceptible cultivar ‘Eston’ and from crosses among the three resistant lines to determine gene allelism. Populations of F1, F2, BC1R and BC1S were screened with two isolates, 91IH and 95B36, separately, both characterized as race Ct1 while F3 families were screened with one isolate, 91IH. Plants were grown under controlled conditions in a growth chamber and inoculated at early flowering with a conidial suspension of C. truncatum. Disease severity was rated 14 days after inoculation as number of lesions on the main stem, depth of penetration and degree of shoot die-back or plant wilt. Chi-square analyses of observed segregation ratios of resistant and susceptible plants in each population revealed that resistance is governed by two recessive genes, ctr1 and ctr2, and three closely linked dominant genes, CtR3, CtR4 and CtR5. The resistance genes ctr2CtR5 in PI345629 and CtR4 in PI320937 were detected by both isolates, while ctr1 and CtR3 in ‘Indianhead’ were detected by isolate 91IH and 95B36, respectively. These data demonstrate that race Ct1 consists of different genotypes, which however cannot be differentiated using the seven resistant lentil lines initially used to characterize race Ct0 and Ct1. A set of lentil lines with single resistance genes is needed to capture more of the pathogenic variability in C. truncatum.