Effects of intracellular and extracellular antifungal compounds produced by bacterial antagonists on the growth of Sclerotium rolfsiiSiwapa Pitisuradech
( M.Sc. )
The soil-borne plant pathogenic fungus, Sclerotium rolfsii causes Sclerotium wilt disease on a wide range of agricultural crops, resulting in severe post-harvest losses. To reduce or substitute agricultural chemical fungicides, the aims of this study were to screen an appropriate culture medium that could enhance the production of an extracellular antifungal compound in Bacillus subtilis SSE4 and Pseudomonas sp. NBR41, and to investigate the antifungal activity of an intracellular antifungal compound and a crude extract of extracellular antifungal compounds of both antagonists on the growth of S. rolfsii. The results found that the extracellular antifungal compounds of B. subtilis SSE4 and Pseudomonas sp. NBR41 that were cultivated in local medium and TSB, respectively, had a good effectiveness in inhibiting the growth of S. rolfsii compared to other culture media. The percentages of fungal radial and submerged growth inhibition by the intracellular antifungal compound of Pseudomonas sp. NBR41 were significantly higher than those of B. subtilis SSE4. In contrast, the percentage of radial fungal growth inhibition by 5% (v/v) of the crude extract of extracellular antifungal compound of B. subtilis SSE4 was significantly higher than that of 5% (v/v) of crude extract of extracellular antifungal compound produced by Pseudomonas sp. NBR41. However, no significant difference in percentage of submerged growth inhibition by both crude extract of extracellular antifungal compounds produced by B. subtilis SSE4 and Pseudomonas sp. NBR41 was observed. Additionally, morphological changes in mycelium of S. rolfsii such as abnormal shapes and hyphal swelling were observed in PDA medium amended with either the intracellular antifungal compound or the crude extract of extracellular antifungal compound of both bacterial antagonists. These results indicated that the intracellular antifungal compound of Pseudomonas sp. NBR41 and the crude extract of extracellular antifungal compounds of B. subtilis SSE4 and Pseudomonas sp. NBR41 could be applied for use as a biocontrol agent for prevention of the disease caused by S. rolfsii in its host plants.