Application of Trichoderma harzianum to control root rot of durian caused by Phytophthora palmivora (Butl.) Butl. in orchard

Trichoderma mix was prepared by amending the powder formulation of T. harzianum (CB-Pin-01) with nutrient additive (rice bran) and organic supplement (compost) at the ratio of 1:4:10 by weight. Efficacy of Trichoderma mix for suppression of Phytophthora palmivora, a causal agent of root rot on durian, was evaluated by using Trichoderma mix applied solely (50 g/square m) or incombination with metalaxyl (Ridomil 5G) at 1 kg/plant or incombination with metalaxyl suspension by spraying and applying to the soil at the rate of 30 g in 20 L of water/plant or combined with the spray of plant health improvement cocktail solution (PHIS). Experiments were conducted in durian orchards at 1) Amphur Klaeng in Rayong province 2) Amphur Muang in Chantaburi province 3) Amphur Khao-saming in Trad province and 4) Chantaburi Horticultural Research Center, Amphur Kloong in Chantaburi province. Results revealed that Trichoderma populations in soil samples collected from all treatments applied with Trichoderma mix were significantly higher (P=0.05) than the population obtained from the control (non-applied soil). The Trichoderma populations obtained were 180, 500, 705.5 and 88.8 fold increase, during the experimental periods of 15 10 8 and 26 months, respectively. Quantification of P. palmivora by baiting and soil dilution plate methods, populations of P. palmivora in all treatments with T. harzianum application were significantly reduced as compared to the control. At Chantaburi Horticultural Research Center, populations of Pythium sp. were also reduced in relative to the control. Evaluation of disease index and plant health before and after T. harzianum mix application was conducted. In durian orchard at Amphur Klaeng, Rayong province, the disease index in the control was increased up to 34.7 percent while the disease index of a treatment applied with respective sites T. harzianum mix integrated with metalaxyl and PHIS decreased by 4.7 percent. At Amphur Muang, Chantaburi Horticultural Research Center, Amphur Kloong, Chantaburi province and Amphur Khao-saming, Trad province, percents of plant health were decreased in all control treatments after the period of experiment; while in the treatments of T. harzianum application with or without metalaxyl, increased percent of plant health or provided undeclining symptom. Efficacy of T. harzianum (M23), the benomyl resistant mutant strain (BRM), was evaluated under green house condition for the antagonistic effect against P. palmivora. Results indicated the reduction of population of P. palmivora in durian soil contained in the clay pots. This BRM strain also reduced Pythium population in soil from Chantaburi Horticultural Research Center, similar to the use of T. harzianum (CB-Pin-01). Determination on population dynamic of T. harzianum (M23) after applied into the soil under durian tree indicated that the fungus could survive and was well established in durian orchard soil. Pathogenicity of Pythium sp. as a causal agent of root rot on durian and the relationship with P. palmivora were determined under lath house condition. Pythium sp. could infect durian and produced root rot symptom as those caused by P. palmivora. Disease severity was increased when the roots were in oculated with both pathogens.