ชีวภัณฑ์ Bacillus subtilis สำหรับควบคุม Rigidoporus microporus เชื้อสาเหตุโรครากขาว และส่งเสริมการเจริญเติบโตของยางพารา

Abstract

Unsuitable soil and nutrient management resulted in rubber trees susceptible to disease, especially white root rot disease. The use of chemicals is ineffective in controlling the disease and affects soil organisms and the environment. The study aims were to develop Bacillus subtilis bio-agent as soluble formula and insoluble formula, the use of biological products in combination with nutrient management on the growth of para rubber, and to control Rigidoporus microporus, caused by white root rot disease of rubber tree. Bacterial antagonists, B. subtilis isolate SM1 and LPDD3-2, B. amyloliquefaciens isolate PT7 were tested against R. microporus fungal mycelium by pour-plate method with potato dextrose agar (PDA). Carriers of bio-agent were tested on the growth of antagonistic bacteria and pathogenic fungi including the effectiveness of inhibiting the pathogenic fungi using PDA containing carriers of bio-agent. B. subtilis bio-agent in granulation form was developed as soluble formula and insoluble formula, and then the physical and biological properties were evaluated. Finally, the effect of bio-agents on germination and growth of rubber trees, including the use of B. subtilis bio-agent together with nutrient management for controlling white root rot disease, was conducted by a randomized complete block design (RCBD) 4 treatments, 4 repetitions, and 8 plants per replication. The results showed that the antagonistic bacteria B. subtilis, SM1 isolate, was the best inhibitor of R. microporus mycelium (97.76 percent). In PDA medium containing carriers of bio-agent, B. subtilis SM1 isolate, soluble formula 1 SM1 was highly in cultured (1.5 ± 1.8 x 1011 cfu/ml) and suppressed R. microporus mycelium (97.78 percent). Preparation of B. subtilis bio-agent appeared that the viable number of B. subtilis isolate SM1 was higher than that of B. subtilis isolate LPDD3-2. Comparison of bio-agent form, it was found that the soluble formula 1 SM1 and insoluble formula 3 SM1 provided the highest viable bacteria of 8.5 ± 1.3 x 1011cfu/g and 9.0 ± 0.8 x 1011cfu/g respectively. Soluble formula 1 SM1 showed high solubility in water in the range of 1.2-1.4 minutes. B. subtilis in the soluble formula 1 SM1 and insoluble formula 3 SM1 showed uniform distribution and 96-99 percent inhibition of R. microporus mycelium. The bio-agent under 10, 28 and 37oC for 12 months storage resulted in the soluble formula 1 SM1, and the insoluble formula 3 SM1 obtained a bacterial viability of more than 109 cfu/g and controlling white root rot pathogens 84-94 percent. Under ultraviolet C (UVC) conditions at a light intensity of 0.1 W/m2, the B. subtilis survival of soluble formula 1 SM1 and insoluble formula 3 SM1 were based on the initial viability of 8.1 x 1011 cfu/g and 7.1 x 1011cfu/g, respectively. The viability of B. subtilis decreased rapidly at 3 h until 96 h. There were 9.6 x 104 and 5.9 x 106 cfu/g, respectively. For the efficacy of the bio-agent under UVC condition at 96 h on inhibition of R. microporus mycelium, it was found that the soluble formula 1 SM1 and the insoluble formula 3 SM1 showed 34-40 percent inhibition of the fungal mycelium, consistent with the surviving number of B. subtilis in bio-agent. The soluble formula 1 SM1 and the insoluble formula 3 SM1 resulted in the rubber growth improvement especially in taproot germination, the amount of fibrous root, plant height, leaves number, fresh weight and dry weight of rubber tree. There was a statistically significant difference (P ≤ 0.05) compared to the non-biological control. In addition, both formulations of Bacillus subtilis also increased the availability of phosphorus in the soil after the experiment by 33 percent. The combination of nutrients with water soluble formulation 1 SM1 and insoluble formulation 3 SM1 resulted in a reduction of white root rot disease. Fertilizer application of 20-8-20 formula obtained in a lower incidence of both above-soil and root of the rubber tree than formula 15-15-15, but there was no statistically significant difference (P ≤ 0.01). B. subtilis bio-agent in the appropriate formulation can increase the B. subtilis efficacy. Bio-agent of B. subtilis in combination with fertilizers can not only reduce disease incidence but also enhance rubber growth. In order to the rubber tree free from white root rot disease and able to grow according to the potential of variety. Therefore, in the management of rubber plantations, Bacillus subtilis bio-agent should be used with appropriate nutrient management.