Diversity of soil microorganisms in banana habitats with and without Fusarium wilt symptom

Fusarium oxysporum f.sp. cubense (Foc), the cause of the Fusarium wilt disease on banana plant, is one of the important soil borne pathogens which may lead to a significant loss of banana yield in Indonesia. This study was done in order to know the soil's microbial diversity in the banana habitat with and without Fusarium wilt symptom. The soil samples were collected from three regencies in Bali, i.e., Karangasen, Klungkung and Jembrana which are the main banana growing areas in Bali. Soil sampling was done in two sites in each regency representing the banana habitat with and without Fusarium wilt symptom, by collecting 100 grams of soil surrounding the banana plant at the depth of 20 cm. Soil microbes population density particularly for bacteria, fungi and actinomycetes were determined based on the plate count technique, while the microbial diversity was determined based on the Diversity Index of Shannon-Wiener. Results of the present study showed that the densiy of soil microbes in the soil of banana habitat without Fusarium wilt symptom (HN) was 13.85 x 10 sup 6 cfu per gram of soil, which was significantly higher than 1.02 cfu per g of soil of banana habitat with Fusarium wilt symptom (HF), while the density of Foc in the soil of HN is 0.003x 10 sup 6 cfu per g of soil, which is lower than 0.01x10 sup 6 cfu per g of soil of HF. The diversity index of the soil microbes in the soil of HN was 2.03, which was higher than 1.91 of HF. The domination index of the soil microbes in the soil of HN was 0.81, which was higher than 0.78 of HF, wherein Bacillus spp. and Pseudomonas spp. were the dominant microbes. The density of soil microbes which are potentially antagonistic against Foc, such as Bacillus spp. Streptomyces spp., Trichoderma spp., Aspergillus spp., Penicillium spp. and Gliocladium sp. is higher in the soil of HN compared to the soil of HF. Among the antagonistic microbes, Bacillus sp. showed the highest inhibitory activity against Foc. These results suggest that the high microbial diversity index, the low population density of Foc, and the high population of antagonistic microbes in the soil of the banana habitat without Fusarium symptom were able to suppress the development of Fusarium wilt disease on banana.