Biodiversity of Rhizospheric Soil Bacteria and ArbuscularMycorrhizal (AM) Fungi in Some of the Wild Medicinal Legumes of Barak Valley

Present investigation was aimed to isolate and study the rhizobacteria and AM fungi from rhizosphere of wild legumes: Mimosa pudica(sensitive plant), Crotolariapallida (Sunhemp), Cassiatora(Sickle pod) andDesmodium.The molecular characterization of four bacterial isolates were done. Four bacterial speciesBacillus megaterium, Bacillusaerophilus, Microbacterium laevaniformans and Staphylococcus xylosuswere isolated from strains M1, RT,D5 and D7 respectively.Also,the distribution of AM fungi population was studied from rhizosphere soils of these legumes.Among the AM fungi,Glomusspecies was dominant and bacterial genus Bacilluswas found to be dominant.Maximum number of VAM infection was found in the rhizosphere soil of Mimosa pudicaof Srikona.


INTRODUCTION
Leguminous plants are abundant in Barak Valley , where they grow in barren soils and drysites that are unsuited for most crops.Medicinal plants are the rich heritage of country serving the age old medicinal system i.e.Ayurveda.Despite being so important these plants have been totally neglected as far as biofertilizers are concerned.For their utilization,medicinal plants are indiscriminately taken from wild habitats causing their depletion andextinction.Pertaining to the negligence toward the rhizobialandVAM biodiversity,we took the initiative to characterize the microbial diversity associated with the medicinal legumes.Rhizobia are of particular interest due to their symbiotic nitrogen fixing ability with members of Leguminosaewhich is the second largestfamily of flowering plants and includes more important drugs than any other family.Rhizobia are genetically diverse and physiologically heterogeneous group  4 .(Bethlenfalvay, 1992).AM fungi (AMF) help plants to capturenutrientssuch as phosphorus and micronutrients from the soil.It is believed that the development ofthe arbuscular mycorrhizalsymbiosis played a crucial role in the initial colonisation of landby plants andin the evolution of the vascular plants.Our present investigation was aimed to isolate and study therhizobacteria and AM fungi from rhizosphereof wild legumes :Mimosapudica(sensitive plant), Crotolariapallida (Sunhemp),Cassia tora(Sickle pod) and Desmodium.collectedfrom Assam university, Rongpur,Irongmara andDoluof Barak Valley.Also,the distribution of AM fungi population was studied fromrhizospheresoils of these legumes.Among theAM fungi,Glomusspecies was dominant.

Experimental sites
Four regions of Barak Valley(Assam University, Rongpur, Irongmara and Dolu) were selected.The vegetation in the valley is mostly Tropical evergreenand there are large tracts of Rain forests in the northern and southern -eastern parts of the valley.

Collection of root nodules
Root nodules offour commonly growing wild legumes Mimosa pudica (sensitive plant), Crotolariapallida (Sunhemp),Cassiatora (Sickle pod) and Desmodiumwere collected and transported to the laboratory in plastic bags along with seedlings.

Isolation of rhizobia
Nodules were separated from the roots and washed in sterilized distilled water for several times.Following serial dilution agar plate techniquebacterial isolation was carried out 5,6 .After that these plates were incubated at 28±1ºC and observed daily.Bacterial colonies appeared after 2-3 days were picked up and streaked on YEMA plates.Pure cultures were obtained with one or more further sub -culturing steps.

Isolation ofVAM andestimatonof AM fungal colonization and AM fungal spores
Staining of mycorrhizal roots were done 7 .VAM isolation was done using wet sieving and decantation method 8 .

RESULTS
Agood number of isolates wereobtained from root nodules ofMimosa pudica(sensitive plant),Crotalaria pallidaSunhemp),Cassia tora(Sickle pod) and Desmodium.Out of the total 20 isolates,only four isolates(M1,RT1,D5and D7)were subjected to molecular characterization test.The isolates were round in shape,gummy white colour,smooth margin and superficial in position.Four bacterial speciesBacillus megaterium, Bacillus aerophilus, Microbacterium laevaniformans and Staphylococcus xylosus were isolated from strains M1,RT1,D5 and D7 respectively as shown below: Further studies on vesiculararbuscular fungal spore population were studied.A total of 17 fungal taxa were isolated from the collected soil samples.The isolated spores belonged to the genusGigaspora,Ambispora, Acaulosporaand

DISCUSSION
The results of present investigation indicated that root nodules of leguminous plants are the habitat of many species of bacteria like Bacillus megaterium, Bacillus aerophilus, Microbacterium laevaniformans and Staphylococcus xylosus.The abundance of root nodules were also studied in the selected plant species.Nodules were highest inMimosa pudica , CrotolariapallidandDesmodium while totally absent in Cassia tora.The absence of nodulation may be due tothe absence of specific no dulating Rhizobiumstrain in therhizospheresoil (Sundar et al).Also, the rhizosphere soils are the habitat of many AM fungal taxa like Gigaspora,Ambispora, AcaulosporaandGlomus.The genus Glomuswas found to be the most dominant,second dominant genus wasGigasporafollowed by Ambisporaand Acaulospora.Further,the number of spores were less in number during Augustand September and gradually increased towards November.Percentage of mycorrhizal infection was studied at five different sites of Cachar district.The percentage of infection was highest in Srikonaand lowest in Dolu area.The variation of percentage infection may be due to the soil characteristics.

Biodiversity of Rhizospheric Soil Bacteria and ArbuscularMycorrhizal (AM) Fungi in Some of the Wild Medicinal Legumes of Barak Valley
3ctendo,arbutoid, monotropoid, ericoid and orchidaceousmycorrhizae), the arbuscularand ectomycorrhizaeare the most abundant and widespread3.(SiddiquiandPichtel,2008). The Vesicular ArbuscularMycorrhiza(VAM) fungi, grouped in the phylumGlomeromycota,are the commonestmycorrhizal type involved in agricultural systems