Vegetative compatibility and heterokaryon stability among diverse Colletotrichum lindemuthianum isolates of Northwestern Himalayan region

Colletotrichum lindemuthianum causes bean anthracnose, one of the deadliest diseases that reduces the bean production significantly. Being an ascomycete and ranking among the top important fungi, the specific causes of its significant variation that renders resistant cultivars inefficient warrant further investigation. In India, several studies have been carried out to examine pathogen diversity. However, mechanisms of the genetic variation, on the other hand, remain elusive. To gain insight, a study was conducted, focusing on the role of mitotic recombination in the development of variability. Vegetative compatibility groups (VCGs), which divide the population into groups that can exchange genetic information via heterokaryosis and the parasexual cycle, are of special importance to asexual fungi. One of the strategies utilized in study on vegetative compatibility groups is obtaining nit mutants. The purpose of this study was to collect heterokaryons from diverse C. lindemuthianum races and isolates, group them into VCGs and examine their genetic variability using the nit mutant system. Twenty single spore isolates yielded 120 nit mutants and were assigned to one of six phenotypic classes: nit 1, nit 2, nit 3, nit 5/6, nit M and CRN (chlorate resistant nitrate utilizing). At the same time, 78 mutants were chosen for anastomosis grouping and were divided into 11 VCGs. We obtained nine (HK 1, HK 2, HK 3, HK 4, HK 5, HK 6, HK 7, HK 8 and HK 9) heterokaryons. Seven of the nine heterokaryons were unstable after eight successive subculturing. Prototrophic development is believed to be supported by continuous anastomosis between nearby homokaryotic hyphae, which restores the heterokaryotic condition. As a result, we speculate that the C. lindemuthianum heterokaryons created are more viable than stable. This study identifies the source of bean anthracnose pathogen diversity in northern India, indicating that we must continue to monitor pathogenic variability and focus our breeding efforts on developing anthracnose-resistant bean genotypes.