Efficacy of indigenous Trichoderma harzianum in controlling Phytophthora leaf fall (Phytophthora palmivora) in Thai rubber trees

Phytophthora leaf fall disease in rubber trees is serious and is known to cause a reduction in both the quantity and quality of rubber latex in Thailand. This experiment was conducted to improve the effectiveness of controlling rubber leaf fall disease in indigenous Trichoderma harzianum. The results indicate that the T. harzianum strain FR-NST-009, isolated from the rhizosphere soil of rubber trees, is more effective at inhibiting the mycelial growth of P. palmivora (66.22%) than the Thai commercial strain T. harzianum CB-Pin-01 (63.51%) with a dual culture technique. This result is clear from the mycoparasitism of the T. harzianum strain FR-NST-009 under scanning electron microscope. Moreover, the ethyl acetate crude extracts of the T. harzianum strain FR-NST-009 with a 500 mu g ml(-1) concentration provided the most efficient mycelial inhibition of P. palmivora by 92.42%. Four bioactive compounds isolated from crude extract and compound 3 provided the highest inhibition of sporangium germination by 98.83%. Compound 3 was then identified as 6-n-pentyl-2H-pyran-2-one using nuclear magnetic resonance spectroscopy. Under field conditions, the T. harzianum strains of RB-NST-028 and FR-NST-009 were able to control leaf fall disease with no significant difference compared with metalaxyl fungicide after inoculation with P. palmivora for 120 days.