MSc

The work was conducted at ICAR- Central Tuber Crops Research Institute, Sreekariyam, Thiruvananthapuram with an aim to study the “Expression of pathogenesis related proteins by plant growth promoting rhizobacteria in controlling taro leaf blight”. Taro is an oldest cultivated crop grown for its edible corms, leaves and also for its broad medicinal properties. Taro leaf blight (TLB) is caused by the pathogen Phytophthora colocasiae and is the most destructive disease which causes about 50% yield loss. The use of resistant cultivars, cultural methods, employing chemical and biological control measures and integrated disease management are different methods for the control of TLB. Muktakeshi and Sree Kiran are TLB tolerant and susceptible varieties of taro respectively. A total of 84 bacterial isolates were taken for screening the most potent bacterial isolates (PGPR) against P. colocasiae by different methods namely, dual culture/direct confrontation, diffusible and volatile metabolites production method. The isolates were also assessed for IAA production. Ten potential bacterial isolates were selected for further study and these isolates were precisely identified by adopting biotechnological tools. The molecular identification of the bacteria revealed that the organisms belong to the genus of Bacillus and Pseudomonas. With an objective to identify the isolates with abilities for pathogen suppression as well as growth promotion, the isolates with good antagonistic potential were assessed for growth promotion in cow pea seedlings. Various growth parameters were observed during specific intervals (at 15, 30, 45 days) after sowing. The results showed that isolate Bacillus amyloliquefaciens (13-14) promotes growth parameters in cowpea plants. This organism was used to carry out experiments for the quantification of defense enzymes. The differential expression of enzymes such as chitinase, glucanase, peroxidase, PAL and total phenol were studied in different treatments using Sree Kiran (susceptible) and Muktakeshi (tolerant) varieties of taro. The results indicated the differential expression of various enzymes such as glucanase, chitinase, PAL etc during different period of pathogenesis. Further growth promotion
and disease suppression potential of isolate, 13-14 (B. amyloliquefaciens) was tested on taro plants. The reduced disease incidence and growth parameters viz., height of the plants, number of leaves, leaf length etc indicated the multipronged potential of the isolate and its suitability to be used as an bio-agent in organic cultivation of taro.