Blue Mold (Penicillium expansum) Decay Resistance in Apple Cultivars, and Its Association with Fruit Physicochemical Traits

Relative resistance of 43 Iranian as well as introduced apple cultivars to blue mold (Penicillium expansum) was studied within years 2010-2011. The fruit physicochemical traits were also evaluated as measures of potential resistance to decay. Local P. expansum strains were isolated from decayed apple fruits and the most aggressive isolate (5,000 spores ml-1) used as inoculum. Fruits were wound-inoculated, and after four months stored in cold storage, decay lesion diameter was recorded. Force to break epidermis, cortex firmness, Total Soluble Solids (TSS) and Titratable Acidity (TA) were determined and their correlation with decay severity detected. Based on the obtained, results significant differences were observed in decay diameters in cultivars and for both years of the study priod. Mashhad was rated as the most susceptible cultivar while Granny Smith as the most resistant one. Relatively, 11.3% of cultivars were rated as susceptible, 54.5% as moderately susceptible, 31.8% as moderately resistant, and finally 2.2% resistant. The cultivars were significantly different in all the physicochemical traits studied. Correlation studies indicated weak negative correlations between decay diameter and TSS, TA, cortex firmness as well as epidermal toughness. Cortex firmness was directly correlated with epidermal toughness and is probable to influence blue mold severity.