36th International Carrot Conference Abstract

Potential for regional level forecasting of Sclerotinia rot of carrot based on distribution or aerial ascospores

M. Parker, M. R. McDonald and G. J. Boland

Department of Plant Agriculture, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada.

Sclerotinia sclerotiorum is responsible for yield losses in a broad range of plant hosts, including carrot. A disease forecasting model has been developed for Sclerotinia rot of carrot (SRC) based on crop canopy closure, temperature and soil moisture. Recently detection and quantification of ascospores of S. sclerotiroum has been added to the forecast model. Currently this is accomplished using a Sclerotinia semi-selective medium in the blue plate test (BPT) with a threshold of 5 ascospores plate^-1. Sets of plates (6 per site) are set out at 3 to 5 sites in the region, 3 times a week, to intercept airborne ascospores. Plates are incubated 3 – 5 days and colony forming units are counted to determine the number of ascospores caught. To improve the efficiency of applying the SRC forecast model, data from nine years of air sampling were analysed to determine the number of sampling sites needed to accurately estimate the concentration of airborne ascospores in a region (ca. 40 km²) of intense carrot production. In six years, ascospore counts were correlated in 20 to 100% of the possible comparisons among air sampling sites. The most consistent relationships among the sites were observed during periods of no detection or detection below the BPT threshold. In most years, periods when ascospore counts surpassed the BPT threshold were consistent among sites, but there were fields and years when these periods were inconsistent. Based on the observations of this combined study, one air sampling site should be sufficient to detect ascospores when counts are low, increasing to two or more sites during periods when ascospores are detected near threshold levels, and cropping and environmental conditions are conducive to disease.

Last updated Thursday, 25-Jul-2013 11:54:08 CDT