Prevalence of collar rot of apple in Himachal Pradesh and its management through antagonistic microorganisms

Surveys were conducted during 2022-2023 to reveal the incidence of collar rot in apple growing locations in the Mandi, Kullu and Shimla districts of Himachal Pradesh. The maximum incidence of collar rot of apple (52 %) occurred in the village Bulash of the Rohanda block, followed by the village Kalashan (40 %) in the Karsog block of the Mandi district of Himachal Pradesh. Phytophthora cactorum was isolated from diseased samples collected during the survey and was identified based on morphological and cultural characteristics. Among the fungal antagonists used in vitro, Trichoderma virens caused the greatest inhibition of pathogen radial growth, with values of 63 % (dual culture) and 40 % (volatile compound evaluation), respectively. Among the bacterial antagonists, the Bacillus cereus group was most effective in dual culture, with growth inhibition of 66 %, whereas volatile compound evaluation of bacterial antagonists revealed that Exiguobacterium aurantiacum caused maximum inhibition (66 %) of P. cactorum in vitro. Among the seven most effective antagonists evaluated under pot conditions, the Bacillus cereus group was the most effective, with a minimum disease incidence of 13 % up to 60 days after pathogen inoculation and a maximum disease control of 85 % in comparison with the positive control.