Research Projects

Citrus microbiome harbours a wide range of endophytic bacteria, fungi and arbuscular mycorrhizal fungi (AMF). Bacterial and fungal endophytes in the microbiome play multiple roles in plant growth and modulate host immune system, while the AM symbiosis confers nutrient uptake, greater tolerance to abiotic and biotic stresses and improves soil structure. Presently, citrus crop in NER India is being threatened by abiotic and biotic stresses causing decline of the citrus orchards. Moreover, erratic rainfall, high humidity, lack of proper soil conservation measures, leads to exposure of the acidic sub surface areas. Drought stress restricts vegetative growth and yield of citrus, adversely affecting fruit quality and results in economic loss. Additionally, Phytophthora foot rot or gummosis of citrus caused by Phytophthora nicotianae (syn. P. parasitica) and P. citrophthora is relatively common in citrus groves in the NE region.

Mapping of Mycorrhiza association in Citrus reticulata grown in the high altitude regions of Sikkim has been done for the first time through this study. AMF species diversity varied along the altitudinal gradient. Root colonization patterns also varied along the altitudes and the age of the host. AMF were purified by single spore culture technique and identified on the basis of morphological keys and reference from INVAM. The dominant species reported in this study are Acaulospora, Rhizophagus, Glomus and Gigaspora. Bacterial strains isolated from different sources were subjected to different in vitro plant growth promoting traits. Bacterial isolates showing multiple plant growth promoting attributes were identified and their ITS sequences have been deposited in NCBI GenBank. Among these Bacilli strains of PGPR viz Bacillus aryabhattai (NCBI: PP410310), B. thuringiensis (PQ270285), B. altitudinis (PQ47446), B.pumilus (PQ474550), B. subtilis (PQ474634) and B. oceanisediminis (PQ474642) are first time report from Sikkim Himalayas to be associated with the rhizosphere of mandarin orange. AMF and PGPR were combined in different compatible combinations and applied to the rhizosphere of Citrus reticulata, under normal conditions, seedlings inoculated with AMF+ PGPR showed maximum responses over control measured in terms of increment in root and shoot length, number of leaves and fresh biomass as well as chlorophyll content in the young leaves with concomitant increment in soil glomalin content, soil acidic and alkaline phosphatases and enhanced mobilization of both macro and micro nutrient in the rhizospheric soil after 1,2 and 3 months of inoculation.