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Poster: Biology & Disease Mgmt: Genetics of Resistance


Evaluating nine boxwood cultivars for susceptibility to Calonectria pseudonaviculata and C. henricotiae.
N. SHISHKOFF (1) (1) Foreign Disease Weed Science Research Unit/ARS/USDA, U.S.A.

Boxwood blight is caused by two species of Calonectria: C. pseudonaviculata (Cps) and C. henricotiae (Che). In North America, only Cps is known to occur, but the 2nd species is of concern since there is evidence that it differs in its temperature optimum, pesticide sensitivity and tolerance to sanitizers. US boxwood cultivars are currently being evaluated for tolerance to Cps and it would be useful to know if their reaction to Che is similar. Based on a previous assessment of susceptibility of 42 boxwood cultivars to Cps, nine were selected on a spectrum from highly susceptible to relatively tolerant. Cultivar sets were inoculated with spore suspensions (mixtures of 4 representative isolates) of each species and the experiment was repeated three times. While results showed some differences in cultivar behavior from trial to trial, there were cultivars that were consistently susceptible (‘Dee Runk’, ‘Vardar Valley’) or consistently tolerant (‘SB17’, ‘Little Missy’) and the interaction ‘pathogen type’*’cultivar’ was not significant. This suggests that breeding for tolerance for one species will confer tolerance for the other.