Asian Research Thesis Index

Abstract

The purpose of the research presented in this dissertation was to determine the physiological responses of crop plants against biocontrol agents (endophytes) in saline environment. In view of substantial reduction in agriculture throughout the world, it is highly important to analyze the effects and mechanisms of salinity related consequences and their remediation in economically important food crops. Based on preliminary study, physiological responses of crop plants using selected endophytes like Trichoderma harzianum (Th- 6) and Paecilomyces variotii (Pv- 14) in saline environment were examined. Trichoderma and Paecilomyces are endophytic fungi that established symbiotic and mutualistic relationship with host plant and supposed to induce salt tolerance. For this purpose, Trichoderma harzianum (Th- 6) and Paecilomyces variotii (Pv- 14) salt tolerant strains were cultured and coated in maize (Zea mays L.) var.NT6621 and rice (Oryza sativa L.) var. Kernel seeds before germination. Later, germinated seeds were allowed to grow at 30±5°C to 22±3°C temperature and 60-70% (RH) relative humidity. Two sets of the experiments were conducted at the same time 1) Plants with endophytes 2) Plants without endophytes. Twenty one day old seedlings of the both the sets of plants were exposed to NaCl concentrations i.e 50, 100 and 150 mM and their physiological responses were examined. Application of endophytes like Trichoderma (Th- 6) and Paecilomyces (Pv- 14) caused substantial enhancement in growth, biomass accumulation, physiological and biochemical traits of plants as compared to those which were not inoculated with endophytes subjected to saline environment. Plants treated with Trichoderma harzianum (Th- 6) and Paecilomyces variotii (Pv- 14) showed higher relative water content (RWC), dark adapted quantum yield (Fv/Fm ratio), performance index (PIABS), photochemical quenching (qP), stomatal conductance (gs) and pigments concentrations as compared to those plants which were treated with salinity without endophytes. In salinity, plants having endophytes triggered considerable increase in antioxidant enzymes actitvities such as catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX). Similarly, antioxidant compounds like free proline, total phenols and carotenoids contents were also increased in endophytes treated plants as compared to untreated plants (without endophytes) under saline environment. It was osberved that MDA and H2O2 contents were decreased due to better antioxidant performance in Th- 6 and Pv-14 treated plants sustaining appropriate osmotic potential under saline environment. In comparsion, it was evident from the study, Trichoderma harzianum strain (Th- 6) induced more tolerance increasing growth, improved photosynthetic and antioxidants performance in plants against salinity as compared to Paecilomyces variotii strain (Pv- 14). Maize plants have shown greater potential to establish symbiotic relationship with endophytes, demonstrating better physiological and antioxidant responses as compared to rice against salinity.

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