| dc.description.abstract | Soya beans are important staple food crops in western Kenya. Legumes play a key role in agriculture by fixing nitrogen in the root nodules in symbiosis with rhizobia. Currently Kenya is experiencing low yield of soya beans, approximately 0.8 t/ha, due to low soil fertility and high cost of inorganic fertilizers and it is a threat to agricultural productivity. Symbiotic rhizobia can increase yields through biological nitrogen fixation. However, the potential of Bradyrhizobium liaoningense in improving yield and productivity of soya beans is not known. Although Rhizobia seem to be widely distributed in the soil, only specific strains of Rhizobia are compatible to specific legumes. There is need to characterize rhizobia species from the wild soya bean to identify effective and compatible rhizobia isolates to host plant to boost nitrogen fixation in the soil hence promote growth and yield of soya beans. Rhizobia bacteria are known to improve growth and yield of several other crops but the effect of inoculating soya beans with B. liaoningense on growth, chlorophyll concentration, nodulation and yields has not been determined. This study aimed at characterization of B. liaoningense bacteria from wild soya beans and determining its inoculation effect on growth, chlorophyll content, nodulation and yields of soya beans (Glycine soja). Sterile root nodules of B. liaoningense obtained from G. soja plants were crushed with pestle and mortar separately by adding small aliquots of sterile water. The purified isolates were inoculated in petri plates containing sterile yeast mannitol agar medium with congo red. Inoculated plates were incubated at 29± 2 °C for 7 days. Pure cultures of the isolates were obtained through re-streaking then the rhizobium characterized morphologically and biochemically. Nine isolates were obtained by preparing pure cultures. Growth tests were carried out in the greenhouse using 5 litres plastic pots of height 25 cm and 23 cm diameter. Pots were each filled with 7kg of top soil. The seeds were treated as: un-inoculated (control), 1.07x107 cfu/ml, 1.19x107 cfu/ml, 1.31x107 cfu/ml and 2.67x107 cfu/ml inoculation of B. liaoningense. The rhizobial colony forming units were established through serial dilution. The treatments were replicated three times and the experiment laid out in the green house in a completely randomised design. Ten seeds of soya beans were sown in each pot. After two weeks of germination, the seedlings were thinned to three plants per pot. Watering was done daily with 200 ml of water per pot up to the end of their physiological maturity. Data on plant height, number of leaves, leaf area, shoot and root fresh weight and dry weight, chlorophyll concentration, number of nodules and number of pods were determined. Data was subjected to analysis of variance. Treatments means were separated and compared using Least Significant Difference at (P = 0.05). Isolates from the wild soya bean nodules had entire margin. The bacterial colony was rod shaped and white in colour. The colonies had raised elevation under microscopic examination. The nine bacterial isolates tested negative by gram staining. Indole test, catalase test, carbohydrate fermentation test, potassium hydroxide test and methyl red test were positive while citrate test and starch hydrolysis test were negative confirming that the nine isolates belonged to the same Bradyrhizobium spp. Soya bean growth and yields after inoculation treatments were found to be significantly different among treatments (P ≤ 0.05). Plant height, number of leaves and leaf area were highest in 2.67 x 107 cfu/ml of B. liaoningense inoculation followed by 1.31x 107 cfu/ml inoculation, 1.19x107 cfu/ml, 1.07x107 cfu/ml and lowest in un-inoculated (control). Inoculation at 2.67 x 107 cfu/ml significantly increased soya bean root and shoot fresh weight and dry weights. Chlorophyll concentration was found to be highest in 2.67 x 107 cfu/ml inoculation and lowest in un-inoculated plants. Inoculation at 2.67 x 107 cfu/ml increased number of nodules of soya beans with increasing rhizobia inoculation. Number of pod per plant were highest at 2.67 x 107 cfu/ml and lowest in un-inoculated (control). These findings show that B. liaoningense inoculation is effective in improving growth, chlorophyll concentration, number of nodules and number of pods in soya beans. From the study it is strongly recommended that B. liaoningense from wild soya bean may be used to improve productivity of soya beans by smallholder farmers. | en_US |
