Native Rhizobia and Phosphate Solubilizing Bacteria as Potential Biofertilizers for Common Bean (Phaseolus Vulgaris L.)

Abstract

Soil fertility decline is one of the major factors that constrains the production of common bean. The use of plant growth promoting rhizobacteria (PGPR) including rhizobia and phosphate solubilizing bacteria (PSB) positively impact common bean production by enhancing nodulation, nutrient uptake, growth and grain yield. This study aimed to evaluate the ability of the native rhizobia and PSB to solubilize phosphates and produce indole acetic acid (IAA) and their potential to enhance common bean growth in the greenhouse. Additionally, the study investigated the suitability of sugarcane filter mud and liquid yeast extract mannitol broth as carrier materials for the survival of bacterial strains under refrigerated and room temperature storage conditions. Field experiments were set up to assess the response of common beans to selected rhizobia-PSB co-inoculation and the efficiency of different inoculant carrier materials. Results from the in vitro studies showed that the tested rhizobia strains have different IAA producing ability and phosphate solubilization efficiency with Rhizobium pusense (S5) and R. phaseoli (B3) produced higher levels of IAA with absorbance values of 1.33 and 1.14 respectively. Similarly, R. pusense (S5) had the highest solubilization efficiency (648), followed by Bacillus megaterium (HK2) (322.3). In the greenhouse study, specific rhizobia-PSB co-inoculation (R. pusense (B2) + B. aryabhattai, R. pusense + B. megaterium and R. phaseoli + B. aryabhattai) significantly increased the number of nodules compared to single rhizobia or PSB inoculation. The highest shoot biomass was observed when R. phaseoli was co-inoculated with P. polymyxa (4.3 g plant-1) compared to the single R. phaseoli inoculation (1.1 g plant-1). The inoculant stored under low temperatures (4℃) had a significantly higher (3.73 x 109 CFU per gram/ml of inoculant) survival than those stored at room temperature (16±2℃) with 2.87 x 109 CFU per gram/ml of inoculant. Storage under low temperature (4 °C) sustained higher viable bacterial cells than at room temperature particularly for liquid inoculant, while filter mud sustained higher population under room temperature. Significantly higher yield (1.64 Mg ha-1) was obtained with the filter mud as carrier materials for the bacterial strains while there was no significant difference in the yield of common bean between peat moss (1.56 Mg ha-1) and YEMB (1.54 Mg ha-1). From this study, it is concluded that co-inoculation of common beans with the specific rhizobia and PSB using sugarcane filter mud as a carrier material significantly enhances nodulation, nutrient uptake, shoot biomass, and grain yield of common bean. This study recommends adoption of co-inoculation of common bean with specific rhizobia and PSB using sugarcane filter mud as a carrier material to maximize common bean growth and yield.