Increasing the Efficacy to Control Narrow Brown Spot of Rice Using Combination of Trichoderma asperellum NST−009 and Bacillus subtilis NST−002

Abstract

Four isolates of Cercospora oryzae, a causal agent of narrow brown spot disease, were isolated from Pathum Thani 1 rice collected from Pak Phanang district in Nakhon Si Thammarat province. All isolates provided 45.84−79.17% of disease severity on leaves of Pathum Thani 1 rice under greenhouse conditions, especially isolate Ce−NST−03 gave the highest disease severity of 79.17%. A total four strains of antagonistic microorganisms (Trichoderma asperellum NST−009, T. asperellum CB−Pin−01, Bacillus subtilis NST−002 and B. subtilis NST−008) were dual culture test on potato dextrose agar (PDA) at room temperature (27 ± 2ºC). All antagonistic strains significantly inhibited mycelial growth of C. oryzae Ce−NST−03 by 38.07−79.34%, compared to the control, especially T. asperellum NST−009 gave the highest inhibition of 79.34%. In the greenhouse test, all treatments with antagonistic microorganisms (individual and two strains combination treatments) significantly reduced disease severity by 26.83−73.17%, compared to the control 2 (with C. oryzae). Treatment with T. asperellum NST−009 + B. subtilis NST−002 gave a highest efficacy to reduce disease severity (73.17%), while using carbendazim chemical gave 70.73% reduction. Moreover, all treatments individual and two strains combination, the antagonistic microorganisms were found to survive in rice leaf by 0.17 × 106−9.22 × 106 CFU per 1 g of rice leaf. Particularly, three treatments with T. asperellum NST−009 (individual), T. asperellum NST−009 + T. asperellum CB−Pin−01 and T. asperellum NST−009 + B. subtilis NST−002 (two strains combination) showed highest rice leaf colonization with the same rate by 100.00%.