Selection of Virulent Isolates of Fusarium circinatum and Investigation of Pitch Canker Severity of Pinus rigida and P. rigida x P. taeda Seed Orchards in Jeju Island

摘要

This study was undertaken to compare and estimate the severity of pitch canker of individual trees of Pinus rigida and Pinus rigida x P. taeda in two seed orchards in Jeju island, in which the orchards have been damaged by the pitch canker for seven years. Wind-pollinated two-year-old seedlings of P. rigida and P. rigida x P. taeda, in which the seedlings of P. rigida x P. taeda were from seeds of phenotypically selected, uninfected(but untested) trees, were inoculated with the pathogenic fungus, Fusarium circinatum, isolated from P. rigida and P. thunbergii. The virulence of the isolates was also identified. Statistically significant difference was found in 'stem cankers'(SC; %2=7.16, P=0.05) among 4 plantations of P. rigida x P. taeda of two seedorchards. P. rigida was higher in 'top kill' (TK) and 'branch tip symptoms' (BT) than those of P. rigida x P. taeda. In artificial inoculation tests, mortality of the seedlings from the resistant candidates was 14% higher than that of the seedlings fromthe susceptible candidates. This result may be caused by unknown pollen trees and/or candidate tree selection based only on phenotypa. Two of five fungal isolates, C-6-L(9) and C-6-L(19), showed significantly higher mortality (68% and 60%, respectively)than others, suggesting that these isolates can be used as virulent isolates for a mass artificial inoculation. Resistance candidate seedlings that were selected from this study can be utilized as useful materials for fundamental studies of genetics andbiochemistry to breed resistance varieties to pitch canker.