Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2003
Publication Date: 12/20/2003
Citation: DEWDNEY, M., CHAREST, J., PAULITZ, T.C., CARISSE, O. MULTIVARIATE ANALYSIS OF APPLE CULTIVAR SUSCEPTIBILITY TO VENTURIA INAEQUALIS UNDER GREENHOUSE CONDITIONS. CANADIAN JOURNAL OF PLANT PATHOLOGY. 2003. 25: 387-400. Interpretive Summary: Most of the work on apple scab in eastern Canada/Northeastern US has been done with the cultivar Macintosh, which is highly susceptible. This study looked at the susceptibility of other widely grown cultivars to apple scab, measuring a number of parameters on the plant, including disease severity, conidial production, number of lesions and surface area of lesions. . 'McIntosh' and 'Vista Bella' were found to be highly susceptible whereas 'Golden Russet', 'Idared', 'Paulared', 'Red Delicious', and 'Sunrise' were the least susceptible. This information will provide an important addition to forecasting models and enable the models to adjust for less susceptibility, with the potential of reducing pesticide applications.
Technical Abstract: Apple scab, caused by Venturia inaequalis, is a disease of great importance in apple production regions in eastern North America. However, little is known regarding the relative susceptibility of North American cultivars to this disease since the majority of previous researches on apple scab were conducted on a highly susceptible cultivar, 'McIntosh'. We evaluated 21 cultivars commonly grown in eastern and central Canada for their responses to V. inaequalis by measuring the following components of partial resistance: the number of lesions per leaf, the number of lesions per square centimetre of leaf, the lesion surface area per leaf, the proportion of leaf area diseased, the number of conidia per lesion, the number of conidia per square centimetre of lesion, the incubation period, and the latent period. All of the components examined were effective in assessing relative cultivar susceptibility, but those related to disease severity, latent period, and conidia production were the most important and accounted for 86% of the variation among cultivars. Numbers of lesions per leaf and per square centimetre of leaf were highly positively correlated with principal component 1 (PC1). Incubation and latent periods were highly negatively correlated with PC1. 'McIntosh' and 'Vista Bella' were found to be highly susceptible whereas 'Golden Russet', 'Idared', 'Paulared', 'Red Delicious', and 'Sunrise' were the least susceptible.