Horizontal tranmission of Cryphonectria hypovirus 1 among different vegetative compatibility groups of Cryphonectria parasitica

Objective: In this study; It is aimed to determine the horizontal transmission capacity of Cryphonectria parasitica hypovirus 1 (CHV-1), which is the biological control agent of chestnut blight, among 25 different vegetative compatibility (vc) groups of Cryphonectria parasitica, which has been recently detected in the Eastern Black Sea Region of Turkey. Materials and Methods: In the study, 48 C. parasitica isolates from 25 different vc groups, whose molecular diagnosis of vic genotype (vc group) have been previously determined with specific primers, were used in horizontal transmission assays of CHV-1. Five of these isolates, whose CHV-1 contents have been previously detected molecularly, were selected as hypovirulent CHV-1 donors to represent different vc groups (EU-1, EU-3, EU-12, EU-45 and EU-51). The remaining 43 isolates having orange colored mycelia without CHV-1 content were selected as recipients. In the horizontal transmission test of CHV-1, the donor isolate and the recipient isolate were grown side by side in PDA medium with 3-4 mm apart each other for hyphal contact. When the colony of the recipient isolate turns into white during mycelial development the horizontal transmisson of CHV-1 from the donor isolate to recipient was defined as a positive. If the recipient colonies continued to develop orange, negative transmision occurs. In doubtful cases, dsRNA analysis was performed on the isolate obtained from the mycelial disc taken from the relevant part of the recipient isolate. Findings: In the CHV-1 horizontal transmission assays performed with C. parasitica isolates from different vc groups, the transmission of CHV-1 was positive in only 20 pairing out of 203 pairing combinations. Poistive transmission of CHV-1 has only occurred in the following pairs: EU-1/EU-21 and EU-60; EU-3/EU-1, EU-10, EU-21 and EU-29; EU-12/EU-21, EU-29, EU-33 and EU-51; EU-45/EU-1, EU-51, EU-21 and EU-60; EU-51/EU-1. Transmission of CHV-1 was confirmed by dsRNA analysis. Conclusion: Results of this study indicated that the transmission of CHV-1 between different vc groups of C. parasitica is significantly inhibited. Although it was observed that CHV-1 was transmissed horizontally at varying rates among certain vc groups, negative transmission has occurred with a high rate of 90.2%. The significant increase in vc group diversity in C. parasitica populations in Türkiye, which has been recently occurring, may adversely affect the spread of hypovirulence in nature, and this may be a factor that may reduce the success of the biological control of chestnut blight. Keywords: Cryphonectria hypovirus 1 (CHV-1), Cryphonectria parasitica, dsRNA, Horizontal transmission.