Susceptibility levels and grouping of peach cultivars in relation to peach rust under field conditions

The objective of this study was to assess susceptibility and classify peach cultivars in relation to rust (Tranzschelia discolor) under field conditions. The study was conducted in an orchard during the 2007/08 and 2008/09 growing seasons and included the cultivars: Aurora 1, Chimarrita, Chiripá, Coral, Eldorado, Granada, Leonense, Maciel, Marli, Premier and Vanguarda. Several disease-related variables were evaluated, over a 10 day interval from September to February, based on estimates of disease incidence, severity and defoliation. The logistic model adequate fit to rust severity progress data (R2 > 0.90) in the two years. Principal component analysis (PCA) using all data, irrespective of the year, identified area under the disease progress curve, initial inoculum and disease progress rate as the best variables to differentiate reactions to rust. When PCA analysis was conducted separately for each year, different disease-related variables were selected as a principal component, and cultivars were classified in three groups of susceptibility. There was inconsistency in the grouping of some cultivars, which was likely due to varying environmental conditions between the years. However, ‘Coral’ was consistently grouped in the low susceptibility group and ‘Chimarrita’ and ‘Granada’ in the high susceptibility group.