Heterothallism among spatiotemporally diverse Colletotrichum lindemuthianum isolates and its implication in common bean anthracnose resistance breeding in the Northwestern Himalayan region

Diverse pathogenic variability in Colletotrichum lindemuthianum is existing in the North Western (NW) Himalayan region. This enigmatic nature of variability has rendered host plant resistance, the most substantial and sustainable disease management approach useless. The frequent resistance breakdown warrants continual spatiotemporal deployment of resistance genes in the host. Therefore, for the durability of resistance genes, there should be an adequate knowledge of the genetic basis of both host resistance and the pathogenicity in the pathogen. In India, several studies have been carried out to characterize the pathogen and to assess the genetic variability in the pathogen. But, the knowledge about the genetic basis of variability is ambiguous. To get insights into the variability mechanism of pathogen and molecular characterization of genes involved in mating, fifteen isolates from Himachal Pradesh and Jammu and Kashmir were crossed in all possible combinations. Isolates showed two classes of interactions with 95% of the combinations showing negative interaction and 5% showed potential type of interaction. The pattern of interaction indicated that the typical bipolar mating or two idiomorphic systems is not responsible for the compatible interactions, rather supports the concept of unbalanced heterothallism. The results indicate that the isolates even being diverse and collected in different years does have mutated alleles at MAT1-2 locus but mutations are not enough for sexual reproduction to occur at significant level between C. lindemuthianum isolates. However, the potential interaction shown by a few isolate combinations indicate sporadic events of recombination among and within the NW C. lindemuthianum populations. Being highly variable pathogen, additional studies are needed to underpin the mechanism of variation in NW C. lindemuthianum population, which is prerequisite to implement better management approaches to counter the pathogen.