Pranab Dutta

Endophytes: exploitation as a tool in plant protection

Endophytes are symptomless fungal or bacterial microorganisms found in almost all living plant species reported so far. They are the plant-associated microbes that form symbiotic association with their host plants by colonizing the internal tissues, which has made them valuable for agriculture as a tool in improving crop performance. Many fungal endophytes produce secondary metabolites such as auxin, gibberellin etc that helps in growth and development of the host plant. Some of these compounds are antibiotics having antifungal, antibacterial and insecticidal properties, which strongly inhibit the growth of other microorganisms, including plant pathogens. This article reviews the endophyte isolated from different plants, mode of endophytic infection and benefits derived by the host plant as a result of endophytism.

Establishment of Metarhizium anisopliae, an entomopathogen as endophyte for biological control in tea

Metarhizium anisopliae is among the ubiquitous members of the soil rhizosphere which also survives as an endophyte in a wide range of plants. The extent of colonization depends on the plant part evaluated and inoculation method used. Current research reveals that foliar spray favours leaf colonization, whereas soil drenching favours root colonization. Besides M. anisopliae, many other fungal isolates were recovered as endophyte which was found to be endosymbiont with each other. Infestation of aphid, Toxoptera aurantii; tea mosquito bug, Helopeltis theivora; termite, Odontotermes obesus; red spider mite, Oligonychus coffeae and carpenter worm, Prionoxystus robiniae was found less in the treated plot as compared to the untreated control. System season long endophytic colonization with the plants suggests a novel approach of biological control of these pests via foliar spray with M. anisopliae for aerial pests and soil drench for soil arthropods. The same entomopathogen was also further confirmed by light and electron microscopic techniques inside the host plant. Molecular study showed that the original culture and endophytic reisolated culture of M. anisopliae were 100% identical to each other.

Effect of Climatic Parameters on Persistence of Metarhizium anisopliae

Effect of Climatic Parameters on Persistence of Metarhizium anisopliae The work has been done on the study related to the persistence of a potential entomopathogen Metarhizium anisopliae outside of their insect host as there is little or no knowledge about the biology. To resolve this question, the study was conducted in organic and inorganic tea ecosystem of Assam. Results have shown that the entomopathogen remained viable and detectable for 1 year and a month in both soil and air in inorganic tea ecosystem. While it was detectable for 1 year and a month in soil and for approximately 12 months in air in organic tea ecosystem, with negative periods between. M. anisopliae this did not persist as epiphyte in the vegetative cover of both the tea ecosystem even for a month after its application. However, its persistence is highly depended upon all the environmental parameters namely temperature, rainfall, humidity, BSSH, evaporation and wind speed. Moreover, soil biological and physico-chemical properties like soil pH, available NPK, exchangeable cations, soil organic carbon and microbial biomass carbon were found to be increased after its application in the studied area. The results of this study showed that the population of M. anisopliae has the potential of accumulating in the soil and air under proper environmental conditions. Conidia present in these areas decay after one year so, fungal spraying must be done accordingly to achieve a better control. We could not able to detect positive colonies of M. anisopliae as an epiphyte in the vegetative cover of the studied area. If conidia are applied on the abaxial surface of leaves, persistence of the entomopathogen could be enhanced on phylloplanes...

Bioefficacy of Metarhizium anisopliae on Aphis craccivora Koch

Laboratory bioassay studies were carried with nine conidial concentrations of Metarhizium anisopliae (Metchnikoff) Sorokin ranging from 1×103 to 1×1011 conidia/ml against the adults of Aphis craccivora Koch. Mortality was monitored at 24 h (1day) interval up to five days. The mortality data indicated that mortality increased with time, and in the highest concentration (1011conidia/ml) 83.83% mortality was obtained. This was followed by a mortality of 64.72 and 52.96% with 1×1010 conidia/ml and 1×109conidia/ml. However, mortality declined with decrease in concentrations with a lowest (17.65%) at 1×103conidia/ml. The results show that M. anisopliae can be used as a promising biocontrol agent for management of A. craccivora.