engleski

Chestnut blight: differential recovery of marrons versus naturally-growing sweet chestnut trees in the presence of hypovirulent Cryphonectria parasitica in natural conditions

For centuries, in Lovran county (Croatian northern Adriatic coast), marrons characterized by large and tasty fruits have been propagated by grafting on naturally-growing chestnuts. Such a practice resulted in the creation of an unique "forest/orchard" of intermixed naturally-growing chestnut trees and grafted marrons. Chestnut blight, a disease caused by the fungus Cryphonectria parasitica has been devastating the chestnuts in that region for decades and the number of marrons was reduced from over 10 000 to only a few hundred trees, despite the naturally-occurring hypovirulence of the fungus caused by the spread of Cryphonectria hypovirus 1 (CHV 1) from 1970s onward. From 2009 to 2011 bark samples from cankers on naturally-growing trees and marrons were collected from Lovran "forest/orchard" and C. parasitica was isolated. Leaves of the same trees were utilized for genotyping chestnuts. All the sampled trees grew on the same soil, in the same geographical location, in the same climate and were more than 70 years old. It was determined that all the trees characterized as marrons belonged to a single clone, while naturally-growing chestnuts showed very high diversity, characteristic for a natural population. Superficial cankers and healing cankers were almost completely absent from marrons while substantially higher incidence of active, deep-expanding cankers was observed on marrons than on naturally-growing trees, despite the fact that there was no statistical difference between the prevalence of C. parasitica vegetative compatibility types and prevalence of associated CHV-1 on naturally-growing trees and marrons. Based on these results we concluded that the lack of naturally-occurring hypovirulence or the diversity of fungal population which would hinder the transmission of CHV1 were not the cause of poor recovery of marrons from the chestnut blight. Ecological differences were ruled out since maroons and naturally-growing trees are growing in close proximity and are of similar age. It seems that the marron genotype is especially vulnerable and its ability to recover is limited even when CHV-1 is widely widespread in C. parasitica population.

chestnut; recovery; hypovirulence

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