Current World Environment

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 rhizobialand VAM 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 Leguminosae which is the second largest family of flowering plants and includes more important drugs than any other family. Rhizobia are genetically diverse and physiologically heterogeneous group Current World Environment Vol. 8(1), 123-126 (2013) Biodiversity of Rhizospheric Soil Bacteria and ArbuscularMycorrhizal (AM) Fungi in Some of the Wild Medicinal Legumes of Barak Valley F. MALINA SINGHA1 * and G. D. SHARMA2 1 Department of Life Science and Bioinformatics, Assam University, Silchar - 788 011, India. 2 Vice Chancellor BilaspurVishwavidyalaya, Vil. SendriRatanpur Rd. Bilaspur Dist. Bilaspur, Chattisgarh - 495 009, India. DOI : http://dx.doi.org/10.12944/CWE.8.1.14 (Received: March 09, 2013; Accepted: March 21, 2013) ABSTRACT 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. Key words: ArbuscularMycorrhizal Fungi, Glomus, Spore population, Diversity. of symbiotic nitrogen fixing bacteria that form nodules on the roots or rarely on the stem of legume hosts, within which thebacteria fix atmospheric nitrogen into ammonia. Leguminous plants are said to behighly specific to nodulatingorganisms.¹ (SubbaRao,1999).

The root nodule formation and fixationof nitrogen from the atmosphere in the rootsof leguminous plants occur only if the specific cross reacting species of Rhizobia is present inthe soil. The production of specific flavonoids by the plants may also attract specificRhizobium strains and facilitate their entry into the host plant and nodule formation.² (SubbaRao,1993). Arbuscularmy corrhizae (AMs) are characterized by the formation of uniquestructures such asarbuscules and vesicles by fungi of the phylumGlomeromycota (AM fungi). Of the seven types of my corrhizae described in current scientific literature (arbuscular, ecto, ectendo,arbutoid, monotropoid, ericoid and orchidaceousmycorrhizae), the arbuscular and ectomycorrhizae are the most abundant and widespread.³ (SiddiquiandPichtel,2008). The Vesicular ArbuscularMycorrhiza (VAM) fungi, grouped in the phylumGlomeromycota, are the common estmycorrhizal type involved in agricultural systems.⁴ (Bethlenfalvay, 1992). AM fungi (AMF) help plants to capturenutrients such as phosphorus and micronutrients from the soil.

It is believed that the development of the arbuscular mycorrhizalsymbiosis played a crucial role in the initial colonisation of land by plants and in the evolution of the vascular plants. Our present investigation was aimed to isolate and study the rhizobacteria and AM fungi from rhizosphere of wild legumes :Mimosapudica(sensitive plant), Crotolariapallida (Sunhemp),Cassia tora(Sickle pod) and Desmodium. Collected from Assam university, Rongpur,Irongmara andDoluof Barak Valley. Also, the distribution of AM fungi population was studied from rhizospheres oils of these legumes. Among the AM fungi,Glomusspecies was dominant.

Materials and Methods

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 technique bacterial 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 of VAM and estimaton of 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 were obtained from root nodules of Mimosa 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 species Bacillus megaterium, Bacillus aerophilus, Microbacterium laevaniformans and Staphylococcus xylosus were isolated from strains M1,RT1,D5 and D7 respectively as shown below: 

Table 1: Assam bacteria: 16S rRNA gene–based identification Click here to View table

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, Acaulospora and Glomus. The number of Glomusspecies were found to be dominantamong all. The following table shows the spore density from some wild legumerhizosphere soil.

Table 2: The abundance of spore population at three sites of  Barak Valley Click here to View table

Table 3: Percentage of mycorrhiza infection in Mimosa pudica at different sites of Cachar district Click here to View table

 

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 in Mimosa pudica, Crotolariapallid and Desmodium 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.

References
 

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