Natural spread of hypovirulent Cryphonectria parasitica strains used for biological control of chestnut blight in Aydın province

Objectives: In the visual examinations conducted annually in chestnut trees treated with hypovirulent strains of Cryphonectria parasitica in the past (2016 and 2017) against chestnut blight in Aydın province, it was observed that hypovirulence apparently persisted in all plots. However, the putative success of hipovirulence has not yet been confirmed with the data obtained as a result of scientific measurements. The aim of this study is to determine the persistence of hypovirulence strains in treated cankers, the recovery of cankers, the survival of trees and natural spread of hypovirulence in the 7th year of hypovirus application to chestnut orchards in Aydın province. Material and Methods: Cankers were evaluated on the treated or non-treated trees in 5 different locations of Aydın Province, namely Efeler Eğrikavak I, Egeler Eğrikavak II, Köşk Sarıçam, Köşk Gökkiriş, Naziili Kuşçular, and Nazilli, Tissue samples were taken from the cankers examined simultaneously (382 samples) and isolation procedures of Cryphonectria parasitica were performed on the samples in the laboratory. Hypovirulence of sampled cankers was evaluated according to the cultural characteristics of the representative isolates corresponding to each sampled canker on nutrient media. For suspicious isolates, dsRNA analysis was performed. Results: In the treatment plots of all locations , it was observed that almost all of the treated trees with hypovirulent strains survived in the 7th year the treatment and active healing tissues were found in all of the treated cankers. Apart from this, the presence of healing cankers was frequently detected both in the untreated sites of the same tree or neighboring trees which were received no treatment. In laboratory studies conducted on the cankered tissue samples, hypovirulent type white mycelial colony forming in C. parasitica isolates were obtained from almost all of the cankers showing signs of healing and thus it was confirmed that most of the cankers showing signs of healing were of the hypovirulent type. The spread of the hypovirulent strains on the same tree was found to be more effective than its spread to surrounding trees. The findings of this study clearly show that hypovirulent strains can survive in natural conditions for many years in the conditions of Aydın province and they can naturally spread with an increasing effect over the years. Conclusion: This study has shown that the control of chestnut blight, which threatens chestnut plantations in Aydın province, is possible with biological control using hypovirulent strains of C. parasitica. In addition, it has been clearly seen that hypovirulent strains can persist in natural conditions for years in Aydın province and that they will spread naturally and have an increasing effect over the years. Keywords: Chestnut, Chestnut blight, Cryphonectria parasitica, Hypovirulence, Biological Control