Influence of biocontrol agents on plant growth and white root rot of apple

Oneyear old apple seedlings were inoculated with biocontrol agents i.e. Glomus mosseae (an endomycorrhiza), Laccaria laccata (an ectomycorrhiza) and Trichoderma harzianum (a fungal antagonist) alongwith Dematophora necatrix (white root rot pathogen) individually and in all possible combinations. All the biocontrol agents enhanced plant height, plant diameter, root length and plant biomass in comparison to uninoculated control or D. necatrix-infected plants. However, maximum increase was noticed in treatments where all the biocontrol agents were inoculated together. Among the individual inoculants, G. mosseae exhibited pronounced effects. After 120 days of inoculation, the disease severity in biocontrol agents inoculated seedlings ranged from 18.4 to 44.0 per cent as compared to 71.0 per cent in uninoculated control. Least disease severity was recorded in seedlings inoculated with all the three-biocontrol agents. After 120 days growth, the mycorrhizal root colonization ranged from 20.2 to 43.3 per cent with less mycorrhization in pathogen-inoculated treatments. The acid phosphate activity in apple rhizosphere was significantly higher in mycorrhiza-inoculated seedlings (32.2–54.3 µM “-nitrophenol released/g soil/hr) than non-mycorrhizal ones (14.2–29.4 µM ñ-nitrophenol released/g soil/hr).