Potential of indigenous bradyrhizobia versus commercial inoculants to improve cowpea (Vigna unguiculataL. walp.) and green gram (Vigna radiataL. wilczek.) yields in Kenya

Abstract

Limited information is available on reduced cowpea (Vigna unguiculata L. Walp.) and green gram (Vigna radiata L.Wilczek.) yields in Kenya. Declining soil fertility and absence or presence of ineffective indigenous rhizobia in soils are assumptions that have been formulated but still require to be demonstrated. In this study, soils were collected from legume growing areas of Western (Bungoma), Nyanza (Bondo), Eastern (Isiolo), Central (Meru) and Coast (Kilifi) provinces in Kenya to assess indigenous rhizobia in soils nodulating cowpea and green gram under greenhouse conditions. Our results showed that highest nodule fresh weights of 4.63 and 3.32 g plant À1 for cowpea and green gram were observed in one soil from Isiolo and another from Kilifi, respectively, suggesting the presence of significant infective indigenous strains in both soils. On the other hand, the lowest nodule fresh weights of 2.17 and 0.72 g plant À1 were observed in one soil from Bungoma for cowpea and green gram, respectively. Symbiotic nitrogen (N) fixation by cowpea and green gram was highest in Kilifi soil with values of 98% and 97%, respectively. A second greenhouse experiment was undertaken to evaluate the performance of commercial rhizobial inoculants with both legumes in Chonyi soil (also from Coast province) containing significant indigenous rhizobia [>13.5 Â 10 3 Colony Forming Units (CFU) g À1]. Rhizobial inoculation did not significantly (P < 0.05) affect nodulation, biomass yield and shoot N content in cowpea and green gram compared with controls. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) of the 16S-23S rDNA intergenic spacer (IGS) region analysis of nodules revealed six groups of which only IGS Group IV corresponded with those from commercial inoculants applied, indicating a lower competitiveness of inoculated strains. In cowpea, IGS III was dominant in nodules of plants inoculated with Biofix and Rizoliq commercial inoculants, and the uninoculated control treatment (63.2, 60 and 52.9%, respectively). Similarly, in green gram, IGS Group III was dominant in nodules of plants inoculated with Biofix 704 and Rizoliq commercial inoculants, and the uninoculated control treatment (75, 73.7 and 61.1%, respectively). Our results suggest that the systematic inoculation of both legumes with current available commercial inoculants to improve biomass yields is not necessary in these regions of Kenya. Also, according to our study, it would make sense to promote the utilization of indigenous strains performing well with both legumes.

Bradyrhizobium Inoculants Enhance Grain Yields of Soybean and Cowpea in Northern Ghana

“…The data from Nyankpala suggest that the indigenous rhizobia were infective but not effective enough to supply the desired N requirement for grain yield to outweigh the control. Some reports from the past suggest that cowpea yields are not improved by rhizobia inoculation (Awonaike et al, 1990; Mathu et al, 2012) but results from Nyankpala showed otherwise. Such conclusions were made by above researchers either because their study sites had large numbers of indigenous rhizobia or the strains used were not effective enough to elicit significant response.…”

Isolation and Characterization of Nitrogen Fixing Rhizobia from Cultivated and Uncultivated Soils of Northern Tanzania

“…However, the rhizobia for nodulating cowpea were relatively high in slightly acidic soils and significantly high in moderately acidic soils. The rhizobia estimates using MPN in soils from Embu district in Kenya varied with the system of land use; the population range for land use under coffee, tea, maize-beans intercrop and fallow was between 1.1 -2.3× 10 2 cells per gram of soil while 6.1 × 10 and 0 cells per gram of soil were recorded for land use under Napier and natural forests respectively [133] [134]. In Poland using MPN technique, R. leguminosarum bv.…”

Advances in plant growth-promoting bacterial inoculant technology: formulations and practical perspectives (1998–2013)

“…For the large majority of developing countries, inoculant technology, especially with PGPB, has no or little impact on productivity of family farms because inoculants are not used, are of poor quality, or are homemade (Bashan 1998). Surprisingly, and probably as a result of the potential for cheaper production of inoculants by small companies, compared to expensive chemical fertilizers and pesticides, many practical studies of numerous crops were performed in developing countries, such as the Indian subcontinent (Johri et al 2003), Vietnam (Cong et al 2009), and on cereals and legumes in Latin America, mainly in Argentina and Mexico (Diaz-Zorita and Fernandez-Canigia 2009;Hartmann and Bashan 2009;Fuentes-Ramirez and Caballero-Mellado 2005) and in Africa (Atieno et al 2012;Mathu et al 2012).…”