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Field and laboratory evaluation of resistance to boxwood blight in Buxus cultivars
M. GANCI (1), K. Ivors (2), D. M. Benson (1). (1) North Carolina State Univ, Raleigh, NC, U.S.A.; (2) North Carolina State University, Raleigh, NC, U.S.A.

Boxwood blight is caused by the fungal pathogen <i>Calonectria pseudonaviculata (</i>=<i>Cylindrocladium pseudonaviculatum</i>=<i>C. buxicola</i>). During 2012 and 2013, a wide range of resistance was observed when <i>Buxus </i>cultivars were inoculated on a container pad, suggesting that some cultivars expressed quantitative resistance to boxwood blight. An experiment was conducted in a growth chamber to evaluate disease severity and quantify the components of resistance. The objective was to compare boxwood blight resistance of intact plants between lab and field tests. Eight cultivars that expressed varying levels of field resistance were spray inoculated with a water suspension of 10,000 conidia/ml and incubated at 20 °C. Disease severity (DS), incubation period, latent period, lesion area, and spore production were evaluated. Significant (<i>P</i> < 0.0001) differences in DS ratings were observed among the cultivars tested. For instance, <i>B. sinica </i>var insularis ‘Nana’ was resistant (7% DS) while <i>B. sempervirens</i> ‘American’ was highly susceptible (89% DS), confirming results with inoculations in the field (‘Nana’ 0.02% DS, ‘American’ 42% DS; <i>P</i> < 0.0001). There was significant (<i>P</i> = 0.0114) correlation between lab and field DS ratings with a Spearman’s rank correlation coefficient of 0.83. Further analysis of the components of partial resistance of <i>Buxus</i> cultivars to boxwood blight can reveal additional lab phenotypic assays that correlate with results from field studies.

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