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Survival and detection of the boxwood blight pathogen in soil.
N. Dart (1), N. SHISHKOFF (2). (1) Virginia Department of Agriculture and Consumer Services,, Richmond , VA, U.S.A.; (2) FDWSRU/ARS/USDA, Frederick, MD, U.S.A.

While many <i>Calonectria</i> spp. have epidemiologically significant soil phases, little research has investigated the soil phase of <i>C. pseudonaviculata</i>. We will discuss an ongoing experiment to determine survival of the pathogen and the invention of a soil detection assay. Survival was investigated in leaves, twigs, and as discrete microsclerotia in sand at two moisture levels and 5 temperatures (-10, 0, 10, 20 and 30 C); after one year, sporulation still occurred on leaves, twigs and from microsclerotia incubated at 0, 10, and 20 C. Plant tissue and microsclerotia incubated at -10 and 30 C rapidly (within 100 days) lost the ability to sporulate or produce mycelium. A leaf disc bioassay for quantifying and detecting <i>C. pseudonaviculata</i> in soil was tested side-by-side with a standard soil plating assay for <i>Calonectria</i>. When compared using three distinct soil types (sand-loam, silt-loam, and sand-peat potting media) over a range of inoculum densities, the optimal incubation time for leaving leaf discs in soil when baiting <i>C. pseudonaviculata</i> was 96 hrs. The optimal soil moisture for the bioassay was 1000% field capacity (soil flooded with 2-4 mm water). The leaf disc bioassay was able to detect <i>C. pseudonaviculata</i> at levels as low as 1 microsclerotium/g soil while the soil plating bioassay was unable to detect the pathogen below inoculum levels of 10 microsclerotia/g soil. Soil type had a significant impact on the sensitivity of both assays.

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