SPREAD OF INTRODUCED HYPOVIRULENCE VS. NATURAL HYPOVIRULENCE IN CHESTNUT BLIGHT

Abstract

Cryphonectria parasitica was found for the first time in Greece in 1963 in Mount Pelion (Central Greece). In a short time the disease of chestnut blight devastated 500 ha of orchard land across the mountain. In 1986, hypovirulence attributed to CHV1 hypoviruses was detected on a single tree at the southern edge of the chestnut area. By the year 2000, hypovirulence had extended spontaneously all over the chestnut area encouraging the revival of chestnut cultivation. During a survey which was conducted in 2008, hypovirulent strains of the only existing vc type EU-12 that were isolated from five plots (207 trees and 130 isolates) varied from 25 to 41.2%. The disease entered the Peninsula of Mount Athos in the 1970s and by 1995 had occupied all 7,000 ha of coppice managed chestnut forest. Hypovirulence was artificially introduced during the period 1998-2000 by inoculating approximately 90 trees/ha in a more or less uniform network. Sampling of non-inoculated cankered sprouts in March 2008 showed that in three plots and out of 344 trees examined and 126 isolates obtained, hypovirulence appeared in 32.6 to 73.3%, significantly higher than in Mount Pelion. It is concluded that systematic inoculation in a dense network of cankered trees may contribute to the establishment of hypovirulence and significantly enhance its spread in comparison with spontaneous appearance and natural spread of hypovirulence. It is the responsibility of the forest manager/orchard owners to decide whether to wait for natural hypovirulence to occur and spontaneously spread or to introduce hypovirulence for quicker results.