Exploring virulence and mating in Colletotrichum lentis

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Colletotrichum lentis is a fungal pathogen that causes an important foliar disease on lentil. Infection, referred to as hemibiotrophic, is complex as C. lentis initially infects without being perceived by the plant (biotrophic phase) before aggressively killing host cells (necrotrophic phase). Understanding the biology of C. lentis in terms of its ecology and its interaction with lentil is the long-term objective of my research program. In the Canadian population, two races were described, the highly virulent race 0 and the weakly virulent race 1. In past research we succeeded in mating isolates of the two races and developed a large population of offspring isolates. The genome of C. lentis was sequenced and with the help of our population, we could arrange the genome into 12 linkage groups probably representing chromosomes. Based on subtle differences in the genetic make-up of the parents (molecular markers) across all chromosomes, we developed a genetic linkage map that can be used analogues to a road map for direction to identify genes involved in controlling traits such as virulence. Using our genetic map and our offspring population we associated differences in the presence of molecular markers among the individuals of the offspring with their virulence on a differential lentil variety. We also associated the markers with the ability to mate, as there are two mating groups in C. lentis, and only two individuals from different mating groups are fertile. We could thus identify one particular chromosomal region that is associated with virulence and another one associated with mating.****These regions consist of many genes and are referred to as quantitative trait loci or QTLs. Not every gene in the QTL will be involved in regulating the trait of interest, so further research is needed to identify those that are. The short-term objectives of my program are therefore to identify and characterize the genes associated with the mating incompatibility QTL and the virulence QTL, and to compare Canada lentil isolates with a Chinese vetch isolate, the first foreign isolate of this species, in terms of mating and virulence. Identification of genes will be achieved by comparing the structure of genes with those that have already been associated with our traits in other species based on conserved features across species. Experiments then will assess whether these genes are affecting the trait by determining whether the fungus “switches on or off” a particular gene when it is infecting a lentil plant, and/or by disabling the candidate gene and assessing changes in the trait, e.g. a prevention of infection by the fungus or two previously fertile isolates becoming infertile. Understanding these traits will enable us to breed for better resistance in lentil varieties because we know what “weapons” C. lentis uses to successfully infect, and what the evolutionary potential of the fungal population is based on its mating system.***