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Application of biological control of chestnut blight on a nationwide scale in Greece: results and prospects

S. Diamandis, C. Perlerou, Z. Nakopoulou, V. Christopoulos, E. Topalidou, G. Tziros
Acta horticulturae 2014 no.1043 pp. 23-34
Castanea, Cryphonectria parasitica, biological control, coppicing, forests, fungi, horticulture, human resources, inoculum, orchards, silvicultural practices, tree age, viruses, Greece
Since 1963 when chestnut blight was recorded for the first time in Greece, the disease has spread into all 29 chestnut growing prefectures. As a result the national, annual chestnut production was reduced from 18,000 tons in the 1960s to 11,000 tons in 2005. A project for the application of biological control on a nationwide scale was funded and implemented during the period 2007-2009. Hypovirulent (hv) strains of Cryphonectria parasitica have been introduced by artificial inoculation into the 17 most important and most heavily infected chestnut growing prefectures. Four vc types were identified in the entire country, those of EU-1, EU-2, EU-10 with the dominant being EU-12 counting for 88%. Hypovirulent inoculum in the form of paste using the spontaneously appearing CHV-1 subtype 1 (Italian subtype) virus was prepared at the Forest Research Institute. It was specific for each prefecture and compatible with the local vc types of the fungus Cryphonectria parasitica according to a vc type distribution map that had been previously elaborated. Three million inoculations in total were made around developing cankers in three consecutive years by trained personnel. An evaluation conducted in 2011 showed that the hypovirulent strains which were introduced had established in all treated areas. Most importantly, the hypovirulent strains had started spreading from the inoculated cankers to non-inoculated ones. The extent of dissemination varied significantly among sampling plots within and among treated prefectures according to the management type (orchards, coppice or high forest), age of trees and horticultural or silvicultural practices applied. The results showed that, only two years after the end of the inoculations, 12.7 to 75.0% of untreated cankers on prefecture scale were healing.