A survey of carrot diseases on muck soils in the Montreal area and evaluation of partial resistance to Cercospora blight in carrot cultivars /

During the summer 1988 and 1989, surveys were conducted on the muck soils, South of Montreal to estimate the prevalence and incidence of the carrot diseases. Cercospora blight was the most prevalent disease; 91% and 96% of the fields and 99% and 92% of the plants sampled were diseased in 1988 and 1989, respectively. In decreasing order of occurrence the diseases present were: Crown gall, Alternaria blight, Root Knot, Sclerotinia rot and Aster yellows.Greenhouse and field studies were carried out to evaluate partial resistance to Cercospora blight in 111 carrot cultivars based on the mean incubation period (MIP), the proportion of leaf area diseased (PLAD), and the sporulation / mm$ sp2$ lesion area (SPO). Significant differences among varieties were observed for all the parameters studied under greenhouse conditions and a significant negative correlation was found between PLAD and MIP (r = $-$0.29). Resistance equivalents were calculated for the PLAD, as proportions of the cultivar Dagger, so that they could be incorporated in a fundamental forecast model