The phylloplane and rhizosphere soil samples were collected from different plants and the bacterial isolates obtained were screened for their efficiency to check Fusarium oxysporum (causal agent of root rot of Vanilla plant). An isolate from rice rhizosphere was found to be efficient in controlling the pathogen, and its growth promoting activity was checked through Indole-3-Acetic Acid (IAA) production. The disease suppression activity was estimated by dual plate assay in vitro and pot culture experiments. The pathogenicity related enzymes such as Phenylalanine Ammonia Lyase (PAL), Transaldolase (TAL), Catalase and Peroxidase, and compounds such as phenols in test Vanilla plants were recorded to be enhanced and correlated with disease suppression.
Vanilla, a herbaceous perennial vine, belongs to the family Orchidaceae, the largest family of flowering plants. Vanilla cultivation is considered as a golden crop because of its high returns next to that of saffron. The global production of vanilla is estimated to be about 5,583 tons per annum. The demand rate is rising by 4-5% every year; while the required gross production in India to meet the requirement of vanilla is 2,020 tons, the production is estimated to be about 404 tons. Even though India has an ideal climatic condition for growing vanilla, the production is still below the expected agricultural value because it is highly susceptible to fast-spreading leaf rot disease. Vanillin, the major product of vanilla, accounts for 70% of flavoring agents used by food industry and is widely employed in perfume industries also. Vanilla production is highly affected by the fungal diseases such as leaf rot, shoot tip rot, stem rot and immature bean rot. All the rot diseases of vanilla are caused by Fusarium oxysporum, which creates the major crop loss to the cultivators.
Fusarium rot of vanilla is treated by a traditional Bordeaux mixture fungicidal application which creates an unexpected environmental pollution and, hence, affects the bio-diversity web of the ecosystem. Several pesticides containing mercury and chlorinated hydrocarbons are costly and begin to accumulate in soil and the water reservoirs, thus affecting the food chain. In order to overcome the above constraints, biological control offers attractive alternative or supplements the use of conventional methods of disease control. Hence, in this study, phyllosphere and rhizosphere bacteria have been characterized for their ability to control the fungal pathogen, both under in vitro and in vivo. The selected one was also checked for its ability to work under open field conditions in a private farm. |
