Potential of Native Rhizobia to Improve Cowpea Growth and Production in Semiarid Regions of Kenya

Julian Wanja Nyaga,Ezekiel Mugendi Njeru

doi:10.3389/fagro.2020.606293

Abstract

Cowpea [Vigna unguiculata (L.) Walp] is an important crop for smallholder farmers in the marginal areas of sub-Saharan Africa. However, the crop growth and production are affected by low soil fertility due to poor soil management practices. Here, we assessed the effect of native and commercially available rhizobia inoculants on cowpea nodulation, growth, and yields on three local cowpea genotypes (K-80, M-66, and KVU 27-1) in the semiarid areas of Kenya. Field experiments were set in smallholder farms during the 2019 and 2020 cropping seasons. Native rhizobia were isolated from root nodules of cowpea plants used as trap cultures. The isolates were further assessed for symbiotic efficiency (SE) in the greenhouse and field experiments carried out during the short and long rain seasons. Field experiments were laid out in a randomized complete block design with three replications. The treatments consisted of the commercial inoculant (Biofix), native isolates, native + Biofix (consortium), and an uninoculated control. In the greenhouse, the native isolates significantly increased nodule number and dry weight (DW), shoot DW, and root DW when compared to the uninoculated control. Additionally, 50% of the isolates recorded SE of &gt;80%, while 35.7 and 14.3% of the isolates had SE of 51–80 and &lt;50%, respectively. In the field, rhizobia inoculation significantly (P &lt; 0.05) increased nodulation and shoot DW compared to the uninoculated controls. Remarkably, rhizobia inoculation significantly increased yields where inoculation with native isolates recorded 22.7% increase in yield when compared to uninoculated control in the first season and 28.6% increase in yield in the second season. However, the rhizobia inoculants did not show a preference for any of the cowpea genotypes, and their performance was influenced by season and the study location. Our results demonstrate the existence of superior native isolates with potential to be developed to low-cost biofertilizer for sustainable cowpea production.

Highlights

Cowpea [Vigna unguiculata (L.) Walp] is an indigenous leafy vegetable and a grain legume widely grown in the semiarid areas of sub-Saharan Africa (Da Silva et al, 2018)
One hundred and three isolates were obtained from the root nodules of the three cowpea genotypes (K80, Machakos 66 (M66), and KVU 271) in the three study regions
All the isolates were Gram-negative and did not absorb Congo red dye when cultured in yeast extract mannitol agar (YEMA) containing the dye and turned YEMA-bromothymol blue (BTB) media from green to yellow

Summary

Introduction

Cowpea [Vigna unguiculata (L.) Walp] is an indigenous leafy vegetable and a grain legume widely grown in the semiarid areas of sub-Saharan Africa (Da Silva et al, 2018). Cowpea production in Africa accounts for over 95% of the global production, serving as a major source of food to millions of people globally (Samireddypalle et al, 2017). The crop provides both nutritional and nutraceutical benefits, including quality and cheap dietary proteins when consumed both as a vegetable and grain legume (Baptista et al, 2017; Da Silva et al, 2018). This, in turn, promotes soil fertility and improve the soil physical characteristics such as the water infiltration and retention capacity (Sánchez-Navarro et al, 2019a,b)

Objectives

Methods

Results

Discussion

Conclusion