Structural and functional characterization of rhizosphere actinomycetes of major crop plants under shifting cultivation practice in Northeast India

This paper aims to study the rhizosphere soils of major traditional crop plants under shifting cultivation of Mizoram for diversity and morphological characterization of actinomycetes, and screening of their salt-tolerance and PGPR activities. The rhizosphere soils from six major crops with adequate replications were collected from two locations (i.e. Reiek and Lengpui, about 30 km apart) of Mamit District of Mizoram. Rhizospheric actinomycetes were isolated by serial dilution method. Purified actinomycetes were screened for their salt resistance under different dilutions (i.e. 0, 50, 70,100, 150, 180, 200, 250, 300 g/l) of NaCl concentrations and their PGPR activities for the production of IAA, siderophores and ammonia. Genomic DNA extraction and their 16SrRNA sequencing of most potential strain AB726 were characterized. Further, rhizospheric soils were studied for their soil physico-chemical properties. A total of 26 rhizospheric actinomycetes were purified and identified. Out of which, five isolates (strain AB726, SKT127, SKT337, SKT97, SKT407) were positive to salt tolerance and one (strain AB726) was strongly positive to all the tested PGPR properties. However, strains SKT725, SKT727, SKT137, SKT197, SKT207, SKT77, SKT177 and SKT337 were positive to ammonia production. Further, strains AB726 was identified as Micrmonospora aurangtinigra based on 16SrRNA sequencing. In conclusion, the changes in microbial population and their functional abilities under shifting cultivation in northeast India depend on the levels of soil physico-chemical properties in different crop soil rhizosphere.