Vegetative incompatibility between Cryphonectria parasitica isolates with identical PCR allele patterns of vegetative incompatibility genes

Hypovirulence-mediated biological control has proven to be one of the most effective measures against Cryphonectria parasitica, the causal agent of chestnut blight. However, the success of this approach is constrained by the vegetative incompatibility (vic) system, which regulates the transmission of hypoviruses. The vic system is governed by six unlinked loci that determine vegetative compatibility (vc) groups. While 64 vc types (EU1-EU64) have been characterized in European C. parasitica populations, the emergence of new genetic variants in certain regions and their incompatibility with European vc testers suggests that the vic system’s complexity is not fully understood. In this study, we investigated the variability in the vic genes of C. parasitica isolates from Türkiye, where genetic divergence has been observed, particularly near the Georgian border. We analyzed the allelic patterns of six vic loci in Turkish isolates with undefined vc groups and compared them to European vc testers. PCR-based genotyping revealed that Turkish isolates belonged to previously known European vc types, including EU3, EU4, EU21, EU29, EU35, EU45, EU51, and EU60. However, significant vegetative incompatibility reactions were observed in co-culturing assays, indicating the presence of intra-group incompatibility even between isolates with identical vic genotypes. Our findings reveal a more complex genetic structure underlying vegetative incompatibility in Turkish C. parasitica populations, challenging the six-locus vic model. The identification of distinct vegetative incompatibility subgroups suggests additional genetic factors at play. This study highlights the need for a deeper understanding of the vic system to improve biological control strategies in Türkiye and beyond.