engleski

Biological control of chestnut blight: persistence of biocontrol agent Cryphonectria hypovirus 1 in healed chestnut cankers

Chestnut blight is a disease caused by the plant pathogenic fungus, Cryphonectria parasitica, introduced to North America and Europe from Asia. The pathogen causes cankers on infected trees. Biocontrol of this fungus is mediated via Cryphonectria hypovirus 1 (CHV1), which reduces virulence and reproductive capacities of the fungus. This phenomenon is called hypovirulence. If the hypovirus is introduced naturally or artificially into active canker (Fig 1a) caused by virulent C. parasitica strain(s), canker expansion ceases and ‘healing’ canker - callus (Fig 1b) is formed. Besides active and healed cankers (Fig 1c), also occurring in nature are superficial cankers caused by hypovirulent C. parasitica isolates, as well as non-expanding, inactive cankers. High prevalence of CHV1 in C. parasitica populations can induce healing cankers and recovery of chestnut forests. Therefore, it is important that hypovirulent CHV1-infected fungal strains persist in populations. The aim of this research was to investigate the persistence of hypovirulent C. parasitica strains in completely healed chestnut blight cankers. Bark samples were collected from seven chestnut populations (six in Europe and one in North America) from more than 100 healed cankers. Samples were taken both from callus tissue and from the callus-wood interface. Neither hypovirulent nor virulent C. parasitica strains comprised more than half of the samples isolated from healed cankers. In different populations, the frequency of hypovirulent C. parasitica strains was different between callus and interface. Generally, virulent C.parasitica strains were found more frequently in healed cankers, which is interesting because hypovirulent strains are thought to promote healing. The relationship between virulent and hypovirulent isolates in healed cankers appears to be highly dynamic. We suspect that the loss of vigor by hypovirulent C. parasitica allows virulent strains or other fungi to invade healed cankers.

biocontrol ; chestnut blight ; hypovirulence

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