Effect of Geosmithia morbida Isolate andTemperature on Canker Development in BlackWalnut

摘要

Thousand cankers disease of black walnut (Juglans nigra) is the result ofaggressive feeding by the walnut twig beetle (Pityophthorus juglandis) andextensive cankering around beetle galleries caused by the fungus Geosmithiamorbida. We developed a consistent, reproducible inoculation technique to screenblack walnut trees for their reaction to canker development following inoculationwith G. morbida. Canker areas in one-year-old trees were not affected by thelocation on the stem that inoculations were made. Differences in aggressiveness ofG. morbida isolates, representing different rDNA ITS haplotype groups, to blackwalnut were observed in some experiments. However, these differences weresmall and evidence indicates that a single, highly aggressive haplotype is notresponsible for the current TCD epidemic. Cankers formed in black walnut at alltemperatures tested, but they were consistently smaller at 32/20°C dayighttemperatures compared to 25/20°C. Although G. morbida is thermotolerant,higher temperatures may not enhance canker development.