Apple scab is one of the greatest apple management problems throughout the world Much work has been done on cultivars resistant to Venturia inaequalis (Cke.) Wint., but few have been a commercial success. This frequently leaves fungicides as the only control method used. As Quebec growers select new cultivars for planting, more information is needed on their relative susceptibility for efficient scab control. In this light, 21 cultivars common to central and eastern Canada, were examined for their relative susceptibility using several components of partial resistance; disease severity, incubation period, latent period, lesion size, and conidial production. The cultivars used were Cortland, Early Geneva, Empire, Golden Delicious, Golden Russet, Idared, Jersey Mac, Jonagold, Jonamac, Lobo, Lodi, Summerland McIntosh, Mutsu (Crispin), Northern Spy, Paulared, Red Cortland, Red Delicious, Royal Gala, Spartan, Sunrise, and Vista Bella. A final ranking of the cultivars and selection of partial resistance components was done using the principal components analysis. (Abstract shortened by UMI.)

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Apple scab is the most important disease of apples in most of the world. The disease, caused by Venturia inaequalis, is controlled by numerous fungicide applications, regardless of the presence of inoculum in the orchard. Better timing of fungicide applications could be achieved if the airborne ascospore concentration (AAC) was considered in decision making. AAC can be measured in real time using spore traps. In this project, the relationship between AAC and lesions development was studied under controlled and natural conditions for five cultivars: Empire, McIntosh, Jonagold, Royal Gala, and Spartan. Potted trees were exposed to different airborne ascospore inoculum and the corresponding AAC were measured using spore traps. The spatial distribution of ascospores was studied in a commercial apple orchard plot. The potential ascospore dose (PAD) and the AAC were measured in 40 quadrats in the spring of 1999. (Abstract shortened by UMI.)

No description available.