Microbiological studies on Rhizobium leguminosarum isolated from pea (Pisum sativum L.)

Rhizobia are the true bacteria that establish symbiotic relationship leading to the development of new root nodules. This study has been designed to evaluate the microbiological aspects of Rhizobium leguminosarum in target area. A total of 1000 (200 from each site) roots were collected from five different agriculture fields (Quetta, Pishin, Killa Abdulla, Kuchlak and Hanna Urak) and screened through different standard microbiological procedures. Results revealed that 665/1000 (66.5%) roots samples were positive for Rhizobium leguminosarum. The highest percentage was from Pishin 180/200 (18%) and Killa Abdullah 160/200 (16%). A remarkable growth of Rhizobium leguminosarum was noted at 28 to 30C whereas, less growth was recorded at 24, 34 and 42C. Similarly, Rhizobium leguminosarum showed growth at pH 5 to 10, but superlative pH values for the growth of Rhizobium leguminosarum were from 6 to 8 pH. The PCR reconfirmed 1300 bp band of 16S rRNA gene of Rhizobium leguminosarum. The organism was further applied as biofertilizer and showed promising results in subjected plants. Medicinal plants application showed that Rhizobium leguminosarum was sensitive to different plants. However, the effects of insecticides showed that Cypermethrin exhibited least zone of inhibition 10 and 11 mm, while Chlorpyrifos showed least zone of inhibition 14 and 17 mm by using disc and well method with (1: 16) dilution. These findings ensure the devastation of microbiota in rhizosphere with rational use of these pesticides that may result in adverse effects over crop productions in the region. Introduction Legumes establish symbiotic relationship in response to nitrogen fixing bacteria that leads to the development of new nodules (Schultze et al. 1998). Soil bacteria play essential and vital role in crop production and different biogeochemical cycles. Plant-bacterial relationships are plant health and soil richness indicator in the rhizosphere. Similarly, free-living soil bacteria are also beneficial for plant growth (Hayat et al. 2010). Certain soil microorganisms are important for the soil life activity, responsible for various decomposition processes involving plants and animals (Gray and Smith 2005). Many legumes have symbiotic bacteria such as, Rhizobia inside the root nodules (Rogers et al. 2007). Rhizobia is extensively used to enhance the capability of legume-Rhizobium synthesis to fix atmospheric nitrogen in agricultural systems. Pea is an annual plant with one-year life cycle that is cultivated in several countries with winter to early summer plantation that may slightly vary in different agro-ecological zones (Zahran 1999). In natural environment temperature, pH, pesticides, medicinal plants are the most important factors that strongly affect many biological aspects of Rhizobium leguminosarum. Therefore, the present study was designed to study the different microbiological and physiological aspects of Rhizobium leguminosarum isolated from pea’s plants of Quetta zone. *Author for correspondence: . Department of Zoology, University of Baluchistan, Pakistan.