Relative Susceptibility of Selected Apple Cultivars to Botryosphaeria dothidea

Abstract

Twenty-three apple (Malus ×domestica Borkh.) cultivars were tested in the field and laboratory for their relative susceptibility to the white rot pathogen, Botryosphaeria dothidea. Wounded fruit were inoculated in the field at 2 to 3 weeks preharvest with mycelium from 14- to 21-day-old cultures. In the laboratory, detached fruit were similarly inoculated. Fruit were rated for relative susceptibility to the fungus with two criteria: disease severity of attached fruit in the field based on lesion growth (mm/degree-day) and disease severity of detached fruit in laboratory inoculations of wounded fruit (mean lesion diameter after 5 days). Based on the laboratory and field data from 2 years of study, cultivars were classified into three relative susceptibility groups: most susceptible: `Fortune' and `Pristine'; moderately susceptible: `Golden Supreme', `Creston', `Ginger Gold', `Sansa', `Golden Delicious', `Senshu', `Orin', `Sunrise', `GoldRush', `Arlet', `Braeburn', `Cameo', `Enterprise', `Fuji', `Shizuka', `Gala Supreme', and NY 75414; and least susceptible: `Honeycrisp', `Yataka', `Suncrisp', and `PioneerMac'. Compared to previous cultivar rankings, the results of the present study indicate that some new apple cultivars from the first NE-183 planting show greater resistance to Botryosphaeria dothidea than current standard cultivars.