Relative susceptibility of selected apple cultivars to Botryosphaeria dothidea

Abstract

Twenty-three apple (Malus xdomestica 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 (ram/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', 'GoidRush', '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.