Fungal Antagonists and Arbuscular Mycorrhizae in Management of Collar and Root Rot Diseases in Apple

摘要

Root rot (Dematophora necatrix) and collar rot (Phytophthora cactorum) kill young plants in nurseries and grown up trees in established apple orchards and cause huge losses. One hundred twenty-two fungal antagonists were isolated from soil of apple orchards and nurseries. While 18 isolates were quite effective in vitro against collar rot pathogen, 15 isolates were found effective against root rot pathogen. Further, pot culture evaluation of these effective fungal antagonists indicated that Trichoderma longibrachiatum-2 was highly effective, when applied (2% bran culture and 0.2 % (w/w) talc based formulation) 20 days prior to pathogen addition, against collar rot disease and showed minimum disease index (PDI of 3.8%). T. harzianum- 3, T. virens- 7, T. viride-5, T. virens -1 and T. viride -1 were also effective in reducing the disease (PDI 7-11%). Similarly, addition of T hamatum -4 exhibited low root rot disease (PDI 6.4%) in pot cultures. T viride 5, T harzianum- 3, 7, and T viride-32 were also effective (PDI 9-15) in pot culture. Disease control increased with the delay in their application time prior to pathogen's inoculation. T longibrachiatum-2 and T. harzianum- 3 were highly effective in controlling collar rot disease in field nursery raised in sick plot (PDI 17-18%). T viride, T virens 1, 7 and Penicillium funiculosum also reduced nursery infection (PDI 20-23%). T harzianum-3, T hamatum 4 and T viride- 5 were most efficient in checking the root rot pathogen in field nursery. Biocontrol agents of mycorrhizal origin isolated from soils of apple orchards and nurseries were also tested in pot culture and in field nursery. Addition of mycorrhizal (Glomus mosseae, G. heterosporum or Glomus -3) infected roots (10 g/kg) of guinea grass (Panicum maximum) to sick soil at 20 days prior to inoculation led to minimum incidence of collar rot disease (PDI 28-30%); Such addition of Glomus mosseae, G. heterosporum or G. macrosporum were also moderately effective against root rot pathogen (PDI 36-42%). Further evaluation in orchard nursery by application of 100 g mycorrhizal infected roots of guinea grass/sick plot of 1m(2) exhibited almost similar results as obtained in pot culture but were less effective in controlling both the diseases.