Isolation and Characterization of Rhizobia from Leguminous Plants and Assessing their Plant Growth Promoting Properties

The increasing world population led to mass application of chemicals in agriculture to increase food production and meet the demand. Today, attentions are diverted into biofertilizers than the chemical fertilizers. This study was initiated to isolate and characterize rhizobia from Faba bean (Vicia faba L.) and assessment for plant growth prompting substance. Faba bean samples were collected by systematic random sampling from farmers’ fields of three geographically varied locations of Tigray region (Korem, mekelle and Tanqa abergele). A total of 90 isolates were subjected to biochemical tests viz. catalase, oxidase, congo red, glucose peptone agar and ketolactose. Isolates were assessed for production of indole acetic acid, ammonia, hydrogen cyanide, exopolysaccharide and for phosphate solubilization. Finally molecular test was carried out for nitrogen fixation and nodulation using nifH and nodA genes. Data on exopolysaccharide production and phosphate solubilization were subjected to statistical analysis. Based on biochemical tests, all the isolates were gram negative, both catalase and oxidase positive. 71 (78.9%) of the isolates didn’t absorb Congo red, 52 (57.8%) showed poor or no growth on GPA and 79 (87.8%) didn’t produce 3- ketolactose. In total, 27 isolates were selected for plant growth promoting properties test. The results showed that all isolates were capable of producing indole acetic acid and ammonia. Whereas, only 3 isolates found to produce hydrogen cyanide. Then 21 isolates were exopolysaccharide producers and the max value (1900 µg ml-1) was produced by isolate Ko1b followed by Ko10c (1850 µg ml-1) and Ta8c (1750 µg ml-1). Similarly, 19 isolates were able to solubilize phosphate with the highest solubilization index (3.33) by the isolate Ko1c. Bands from the gel showed that about 781bp nifH gene and about 850bp nodA gene fragments were found in some isolates. Generally, the potential isolates throughout the tests are promising and important to be used as bioinoculant production. But large scale bioinoculant production must be after field trial of isolates because in vitro results may not be the same as in vivo based experiments.