Preparation And Biological Effects Of A Bio-Organic Fertilizer Against Banana Fusarium-Wilt Disease

Banana is one of the most important fruit in the world. However, banana production has been restricted due to long-term monoculture system. Fusarium wilt of banana is one of the most destructive worldwide diseases of banana. Breeding of culitvars with resistance to fusarium wilt, chemical application and field management are among the solutions to control this disease. However, it is necessary and urgent to find a better way to ensure banana industry worldwide. Biocontrol has been proven to be economical and environment-friendly for overcoming such soil-borne disease.A pathogen (Fusarium oxysporum f. sp. cubense) of banana wilt disease was first isolated from the infected banana plants, and then a high efficient antagonist was screened and fermented with organic fertilizer (pig manure compost and amino acid fertilizer) to prepare a bio-organic fertilizer. A series of laboratory and greenhouse experiments were conducted to investigate the growth-promotion and disease-suppressive effects of the bioorganic fertilizer on the banana plants. The results were as follows.The pathogen was isolated from the compartment of pseudo-crown of diseased banana by using selective medium. According to the symptoms, morphology and pathogenicity, the pathogen was identified as Fusarium oxysporum that had a high pathogenicity from a pot experiment, in which the disease incidence was 90% and mortality rate was as high as 70 % on 35 days after inoculation of pots with the pathogen. Therefore, the pathogen was identified as Fusarium oxysporum f. sp. cubense.A close relationship between the amount of inocula in bulk soil and the disease incidence rate of banana wilt was found. The minimal concentration that induced the banana Fusarium wilt was 103cfu/g soil. Disease incidence was increased with the increase of inoculum density in bulk soil. When the inoculum density was more than 105cfu/g, the disease incidence remained a high level of infection. The numbers of pathogen in rhizosphere soil were 1.15 to 2.06 times higher than those in bulk soil in each treatments. This result gave a very important clue for people to forcast disease, though the disease incidence was usually determined by the number of the pathogen in plant roots. Two strains N-6 and N-11, which showed high antifungal activity against F. oxysproum f. sp. cubense, were obtained from the healthy rhizosphere and bulk soil in the banana plantation that was seriously infected with Fusarium wilt(Fusarium oxysporum f.sp.cubense). Results from morphological and physio-biochemical identification and 16S rDNA sequence analysis showed that both N-6 and N-11 belonged to Bacillus subtilis. The optimal fermentation conditions for strain N-6 were:temperature at 30℃, initial pH value from 5.7 to 6.9, glucose or maltose as carbon source, and peptone or yeast extract as nitrogen source, while those for strain N-11 were:temperature at 28℃, initial pH value from 4.7 to 6.0, sucrose or maltose as carbon source, and peptone or yeast extract as nitrogen source.Organic fertilizer (pig manure compost and amino acid fertilizer) were innoculated with strain N-6 and N-11 for a second solid fermentation to produce bioorganic fertilizer, which was applied to soil to investigate effects on the growth of banana plants in greenhouse. Thirty days after transplating the banana plants, plant height, fresh weight, leaf area, chlorophyll content and root activity were increased by 23.5% to 54.4%,23.0% to 180.0%,85.0% to 123.0%,20.4% to 24.5%, and 34.0% to 174.0%, respectively, in the bioorganic fertilizer treatments when compared with the control (CK). In contrast to the control, the numbers of rhizosphere bacteria, fungi and fungi/bacteria ratio of the soils applied with bioorganic fertilizer were increased, particularly for the treatment amended with the bioorganic fertilizer fermented with mix culture of strain N-6 and strain N-11 (T5). In the treatment of T5 and the treatment that amended with the bioorganic fertilizer fermented with strain N-6 (T3), suppressiveness rates against Fusarium wilt were 82.0% and 86.0%, respectively, fifty six days after transplanting.Forty five days after transplantation, we determined some enzyme activities of banana plants in all treatments. Activities of chitinase andβ-1,3 glucanase in the treatments of bioorganic fertilizer application were 2.64 to 12.88 and 5.22 to 7.22 times higher than that of CK, respectively. Callose contents in root tip and plant stem from the treatments of bioorganic fertilizer application were decreased by 59.7% to 77.9% and 47.6% to 68.9%, respectively, as compared with CK. The numbers of bacteria and actinomycetes in rhizosphere of the soils applied with bioorganic fertilizers both in nursery and transplanting stage were increased by 1.56 to 1.76 and 1.34 to 1.50 times higher than that of CK, respectively, while the numbers of fungi and Fusarium Oxysporum were reduced by 19.2% to 29.6% and 38.0% to 63.9%, respectively, as compared with that of CK. The results suggested that the application of bioorganic fertilizers to soil could significantly promote the growth of banana plants and suppress Fusarium wilt.We concluded that the specific bio-organic fertilizer against banana Fusarium wilt could effectively control the disease by improving the banana rhizosphere microbial diversity, increasing plant enzyme activities related to pathogen resistance and promoting plant growth.