Genetic Control of Resistance to Colletotrichum kahawae in Coffee: Evidence of Polygenic Inheritance and Differential Host Genotype Responses to Pathogen Isolates

Colletotrichum kahawae is the causal agent of coffee berry disease (CBD), a disease restricted to African countries producing C. arabica, which affects coffee production and is a potential phytosanitary threat for coffee plants growing at other latitudes. The inheritance of resistance to C. kahawae conferred by the R gene (Ck-2/Ck-3) in the Rume Sudan variety of coffee was previously reported as simple Mendelian (3:1). However, our results derived from an F2 population of 10,180 hypocotyls, similar to the resistance observed in Rume Sudan against C. kahawae, reveals a polygenic involvement. Therefore, resistance to CBD cannot be explained by a Mendelian segregation model, since the observed phenotypic interactions reveals that resistance involves a system of genes [quantitative trait loci (QTLs)]. Similarly, the genetic potential for resistance of a wild genotype of C. arabica ET.56 to C. kahawae was evaluated, and its segregation was also evident in its phenotypic interactions, similar to that of Rume Sudan. However, differences in the phenotypic expression of their segregated populations potentially suggest that the genetic mechanisms responsible for resistance to C. kahawae in these two varieties are likely different. Finally, statistical analysis revealed the existence of the C. arabica/C. kahawae interaction and the consequent existence of pathotypes, demonstrating that resistance is not transversal but specific to C. kahawae isolates. This behavior is consistent with that previously reported based on the genetic diversity of C. kahawae and can be used in genetic improvement programs for C. arabica to enhance the development of varieties resistant to the disease.