MICROBIAL DIVERSITY IN NITROGEN FIXING NODULE OF CASUARINA EQUISETIFOLIA AND ITS IMPACT ON PLANT GROWTH AND SOIL QUALITY

Abstract

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Actinorhizal plants can contribute to the rehabilitation of poor and disturbed soils by stabilizingthe soil and building up its nitrogen content. In addition, they can withstand under variousenvironmental stresses such as high salinity, heavy metal, etc., Casuarina equisetifolia is an actinorhizal plant which is important in agroforestry, land reclamation and natural ecosystems. The aim of this study was to explore microbial diversity in nitrogen fixing nodules of C. equisetifolia and to assess its impact on plant growth and soil quality. Double layered agar plate technique was adopted to isolate microorganisms from surface-sterilized root nodules. Isolated microorganisms were identified based on distinctive morphological characteristics of colonies and mycelia which were observed under light microscope. Ability of isolates to grow with cadmium up to 10 mg/mL was also tested.Two weeks old seedlings of C. _ • equisetifolia which were grown in V* strength Hoagland’s nutrient solution (pH 6.8)7were inoculated with different isolates to examine infectivitv. nodulation and their effect on shoot and root growth of C. equisetifolia. The root, shoot length, lateral root formation, nodulation were recorded. The plant assay was conducted in triplicate in a completely randomized block design. Three actimomycetes species .Frankiasp., Micromonospora sp. and Streptomyces sp.were identified from nitrogen fixing root nodules. Further, synergistic growth of all three isolates in liquid media with and without any nitrogen supplement was observed. While Frankia sp. promoted the shoot and root growth by 87% arid 55% respectively with nodulation of C. equisetifolia, about 28% increase in shoot and root growth of C. equisetifolia by Micromonospora sp. without nodulation was observed. In contrast, lateral root formation ofC.equisetifolia found to be triggered by Streptomyces sp. indicating its potential to modulate host developmental pathways. This study provides novel data on isolation of root inhabiting Streptomyces sp. which could probably play a vital role in exchanging complex signals between plants and the microorganisms and alleviating cadmium toxicity to the plant by depleting caecum availability in soil. In conclusion, the plant probiotic role of nodule inhabiting actinomycetes of C. equisetifolia v/ovid significantly contribute to the plant growth and soil quality.