Susceptibility to blue mold caused by penicillium apple cultivars adapted to a cool climate

Abstract

Each year, fungal storage rots cause serious losses in the apple industry. The problem is especially prominent in production systems with little or no use of pre- or postharvest fungicides. Consequently, a high level of tolerance to storage rots is very desirable. A set of 81 apple cultivars were studied in two different production areas (Nj0s in Norway and Balsgard in Sweden), during two seasons (2012 and 2013), to investigate genetically determined susceptibility to blue mold, Penicillium expansion. Lesion diameter, measured on symptoms developing after artificial inoculation with this pathogen and cold storage for 6-12 weeks, and decay index, calculated as lesion diameter divided by number of weeks in storage, varied significantly among cultivars. Associations between disease evaluation data and different fruit characteristics were also investigated. Decay index was negatively correlated with harvest date, estimated as number of days since full bloom, and fruit firmness at harvest. A positive correlation was instead found between decay index and amount of fruit softening during storage. These results provide data about genetically determined level of resistance to blue mold for apple cultivars adapted to a cool climate, and will be valuable for further research on the genetic control of resistance, as well as for choice of breeding material.