Determination Of Biodiversity And Symbiotic Efficiency Of Native Rhizobia Isolated From Different Regions In Kenya

ABSTRACT

Crop production has continued to decline in sub-Saharan Africa due to soil infertility and increased cost of farm inputs. To enhance food security, farmers have adopted the use of both inorganic and organic fertilizers on their farms. The production and use of inorganic chemical fertilizers are not only expensive for family farming systems but also contribute significantly to environmental pollution. Biological nitrogen fixation using rhizobia has proven to be a cost-effective and environmentally friendly alternative to inorganic nitrogen fertilizers. Rhizobia interact with legumes symbiotically, improving soil fertility and legume plants productivity. The present study aimed at determining the morphological and genetic diversity, cross-inoculation ability, and symbiotic efficiency of native rhizobia isolates in sterile and non-sterile soils. Greenhouse experiments were set to trap rhizobia from soil from smallholder farms from Kitui, Embu, and Tharaka Nithi Counties using cowpea as the trap host. The cowpea crops were harvested after one month, and a total of 311 nodule isolates were purified from the crop nodules. Based on morphological characteristics, the nodule isolates were clustered into 42 different groups. The effect of the soil on cowpeas nodulation was determined using redundancy analysis where soil characteristics including P, Zn, Mn, and total organic carbon correlated positively with cowpea nodulation and nodule dry weight. Soil pH and Ca correlated negatively with nodule number and weight. In addition, 53 glycerol stocks nodule isolates (archived samples) from previous studies were revived. Revived cultures were clustered based on morphological characteristics into 11 different groups. The isolates were tested for symbiotic efficiency using common bean, cowpea, green gram and soyabean seeds planted in sterile and non-sterile soils in the greenhouse. Un-inoculated plants were used as controls, while the treatments included the revived native isolates and commercial rhizobia inocula. The experiments were laid out in a completely randomized design. Plants grown in both sterilized and non-sterilized soils and inoculated with the different isolates varied significantly (p