Investigating the bioactivity of cells and cell-free extracts of Streptomyces griseus towards Fusarium oxysporum f. sp cubense race 4

The antifungal activity of viable cells of Streptomyces griseus (St 4) and its cell-free extracts were investigated against the pathogenic Fusarium oxysporum f. sp. cubense race 4 (FOC race 4), causal agent of wilt disease in bananas. Results from in vitro and soil assays showed cells and cell-free extracts of S. griseus were able to inhibit FOC race 4 with varying degree of success. Antifungal activity was attributed to chitinase and beta-1,3-glucanase, detected in both cells and cell-free extracts, which caused lysis of fungal cell wall and inhibited sporulation. Interestingly, beta-1,3-glucanase and chitinase activities were significantly higher in cell-free extracts compared to cells, with 8.30 and 5.43 against 7.96 and 4.95 U mL(-1), respectively. Application to soil however, showed inoculation using S. griseus cells were more effective in suppressing growth of FOC race 4 than crude extracts, with 6 log(10) CFU of FOC race 4 g(-1) soil enumerated compared to 7 log(10) CFU of FOC race 4 g(-1) soil after 20 days. To summarize, this study has shown that cell-free extracts of S. griseus have antifungal properties but may not be suitable for soil application in its current form (liquid suspension). Further investigations on bioformulation may address this limitation. (C) 2013 Elsevier Inc. All rights reserved.