Temporal scab progress of each classification category was analyzed by (i) calculating standardized area under the disease progress curves (AUDPCS) (ii) fitting a three-parameter logistic function to the disease progress data and (iii) estimating upper asymptote (yf), relative rate parameter, and the inflection point from the fitted function. The resistance of old cultivars to scab ranged from low to moderate to high. Categorization of cultivar susceptibility indicated that season-long leaf and fruit scab development was low for the majority of resistant cultivars and moderate to high or high for most commercial cultivars. Fruit of all cultivars was protected in the integrated production system (final fruit scab was below 1.1%), but most commercial cultivars (‘Idared’, ‘Jonagold’, ‘Jonathan’, ‘Jonica’, ‘Mutsu’, and ‘Royal Gala’) were moderately or highly infected by harvest in the organic production system. Mean final scab incidence was considerably higher in the organic than in the integrated production system except for the resistant cultivars, which had no fruit scab symptoms. In a 7-year Hungarian study, 27 apple cultivars (9 scab resistant, 9 commercial, and 9 old) were evaluated for scab resistance in high-density integrated and organic apple orchards classified into five susceptibility categories (low, low to middle, middle, middle to high, and high) based on their season-long leaf and fruit scab development and the temporal progress of scab in each classification category was analyzed.
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December 2022
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