Efficacy of biocontrol agents in improving plant growth and control of Pythium root rot in apple

One-year old apple seedlings of cv. ‘Red Delicious’ were inoculated with biocontrol agents viz., Glomus mosseae (an endomycorrhiza), Laccaria laccata (an ectomycorrhiza) and Trichoderma harzianum (a fungal antagonist) in presence of root rot pathogen, Pythium ultimum, to assess their impact on seedling growth and disease control. All the biocontrol agents significantly enhanced plant height, seedling diameter, root length and plant biomass as compared to uninoculated or pathogen-inoculated controls. Maximum increase, in above parameters, was observed in G. mosseae-inoculated seedlings. The disease severity after 120 days of pathogen-inoculation in biocontrol-inoculated seedlings was significantly less than observed in pathogen-inoculated seedlings (control). The disease severity in biocontrol agents-inoculated seedlings ranged from 19.2 to 24.9 per cent as compared to 52.4 per cent in pathogen-inoculated control. The mycorrhizal root colonization ranged from 17.9 to 34.2 per cent with less mycorrhization in pathogen-inoculated treatment. The acid phosphate activity was significantly higher in mycorrhiza-inoculated seedlings (30.5–38.8) µM p-nitrophenol released/g soil/hr) than non-mycorrhizal ones (14.9–29.6 µM p-nitrophenol released/g soil/hr).