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Poster: Biology & Disease Mgmt: Genetics of Resistance


Virulence of Calonectria pseudonaviculata and C. henricotiae isolates and screening for resistant boxwood cultivars in detached leaf assays
H. Guo (1), J. Crouch (2), M. Pooler (3) (1) USDA-ARS and Rutgers University, U.S.A.; (2) USDA-ARS Systematic Mycology and Microbiology Laboratory, U.S.A.; (3) USDA-ARS US National Arboretum, U.S.A.

Boxwood blight caused by the two Calonectria species, C. pseudonaviculata and C. henricotiae, is a recently emerged threat to the annual $1.3 million boxwood industry. While fungicidal control can be effective, breeding resistant or tolerant cultivars is the preferred long-term strategy to control the disease in the landscape. Developing an effective assay to quickly screen potentially thousands of boxwood genotypes is an essential first step in such a breeding program. Therefore, this study was conducted to evaluate the virulence of different Calonectria isolates on a susceptible boxwood host. The virulence of 24 isolates was determined by inoculating detached leaves of Buxus sempervirens 'Suffruticosa' using two different inoculation techniques. All 24 isolates were virulent on ‘Suffruticosa’, but the virulence varied among isolates. The isolate NCBB-1 was the most virulent, and was used to compare relative resistance among eight diverse boxwood taxa. Preliminary results indicate that two boxwood taxa, B. harlandii and B. sinica var. insularis ‘Nana’, are the most tolerant to this isolate in detached leaf assays.