สภาวะที่มีผลต่อการเจริญเติบโตของแบคทีเรียปฏิปักษ์ Bacillus subtilis เพื่อการควบคุม Rigidoporus microporus เชื้อสาเหตุโรครากขาวของยางพารา

Abstract

This research aimed to investigate suitable food sources for the growth of Bacillus subtilis (SM1 and LPDD3-2 strain) to control Rigidoporus microporus (NK6 strain) fungus and promote plant growth. The result showed that rice bran (1 and 3 percent) and broken rice (3 and 5 percent) are the most favorable carbon sources for cultivating and increasing the quantity and quality of B. subtilis strains. The cell count of both strains increased, reaching 12.20 and 12.16 log CFU/ml respectively. The concentration 3 percent of rice bran and broken rice directly correlated with the quantity of B. subtilis strains, with rice bran showing a more favorable response. However, at all concentration of broken rice, R. microporus strain NK6 grew well, but all concentrations of rice bran were added to the medium, the growth of mycelium decreased by 4.3 and 3.6 cm, respectively. It was found that the supernatant and volatile compounds of B. subtilis strains were able to inhibit the growth of R. microporus strain NK6 by more than 80 percent, such as rough mycelium, uneven fiber sizes, distorted growth and distend end of mycelium. Then, some constituents of the extracts from the two strains of B. subtilis strains were examined by TLC and NMR. The extracts showed signs of olefinic proton, aliphatic proton and aromatic proton, suggesting that both strains of B. subtilis were examined able to produce biosurfactants and release them outside the cell. For the study of the properties of Para rubber growth promoters, it was found that B. subtilis was able to synthesize the highest IAA content of 276.857 and 263.659 µg/ml that were cultured with rice bran and broken rice at the concentration of 3 percent. As a result, the growth of Para rubber in height, root length, leaf number, fresh weight and dry weight were not statistically different. However, both strains of Bacillus subtilis antagonistic bacteria were more likely to promote the growth of Para rubber. It may be possible that these antagonistic bacteria strains could enhance plant health, leaf and root development. Therefore, the bio-agent development of B. subtilis antagonistic bacteria for controlling R. microporus by using rice bran in culture medium of B. subtilis and as an ingredient in bio-agent is an approach that should be further studied.