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. 2017 Mar 31:8:443.
doi: 10.3389/fpls.2017.00443. eCollection 2017.

Potential of Native Rhizobia in Enhancing Nitrogen Fixation and Yields of Climbing Beans (Phaseolus vulgaris L.) in Contrasting Environments of Eastern Kenya

Gilbert Koskey  1 , Simon W Mburu  1 , Ezekiel M Njeru  1 , Jacinta M Kimiti  2 , Omwoyo Ombori  3 , John M Maingi  1
Affiliations

Potential of Native Rhizobia in Enhancing Nitrogen Fixation and Yields of Climbing Beans (Phaseolus vulgaris L.) in Contrasting Environments of Eastern Kenya

Gilbert Koskey et al. Front Plant Sci. .

Abstract

Climbing bean (Phaseolus vulgaris L.) production in Kenya is greatly undermined by low soil fertility, especially in agriculturally prolific areas. The use of effective native rhizobia inoculants to promote nitrogen fixation could be beneficial in climbing bean production. In this study, we carried out greenhouse and field experiments to evaluate symbiotic efficiency, compare the effect of native rhizobia and commercial inoculant on nodulation, growth and yield parameters of mid-altitude climbing bean (MAC 13 and MAC 64) varieties. The greenhouse experiment included nine native rhizobia isolates, a consortium of native isolates, commercial inoculant Biofix, a mixture of native isolates + Biofix, nitrogen treated control and a non-inoculated control. In the field experiments, the treatments included the best effective native rhizobia isolate ELM3, a consortium of native isolates, a commercial inoculant Biofix, a mixture of native isolates + Biofix, and a non-inoculated control. Remarkably, four native rhizobia isolates ELM3, ELM4, ELM5, and ELM8 showed higher symbiotic efficiencies compared to the Biofix. Interestingly, there was no significant difference in symbiotic efficiency between the two climbing bean varieties. Field results demonstrated a significant improvement in nodule dry weight and seed yields of MAC 13 and MAC 64 climbing bean varieties upon rhizobia inoculation when compared to the non-inoculated controls. Inoculation with ELM3 isolate resulted to the highest seed yield of 4,397.75 kg ha-1, indicating 89% increase over non-inoculated control (2,334.81 kg ha-1) and 30% increase over Biofix (3,698.79 kg ha-1). Farm site significantly influenced nodule dry weight and seed yields. This study, therefore, revealed the potential of native rhizobia isolates to enhance delivery of agroecosystem services including nitrogen fixation and bean production. Further characterization and mapping of the native isolates will be imperative in development of effective and affordable commercial inoculants.

Keywords: Eastern Kenya; biological nitrogen fixation; climbing beans; ecosystem services; native rhizobia.

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Figures

Figure 1
Figure 1
Correlation analysis between nodule dry weight and shoot dry weight in the greenhouse.
Figure 2
Figure 2
Correlation analysis between nodule dry weight and shoot nitrogen in the greenhouse.
Figure 3
Figure 3
Interactive effects of farm location with rhizobia inoculants on % shoot N of climbing beans. Bars followed by the same letter are not significantly different according to Tukey's HSD test at P ≤ 0.05. ELM3, Test native rhizobia isolate; TC, Consortium of native rhizobia; TB, Commercial inoculant (Biofix); TCB, Biofix combined with consortium; TUC, Negative control (Non-inoculated); ELM, Embu Lower Midland; EUM, Embu Upper Midland; TLM, Tharaka Nithi Lower Midland; TUM, Tharaka Nithi Upper Midland.
Figure 4
Figure 4
Effects of the main factors on climbing bean yield parameters in the field. (A) Effect of rhizobia inoculation on pod number. (B) Effect of rhizobia inoculation on seed yield. (C) Effect of farm site on pod number. (D) Effect of farm site on seed yield. (E) Effect of bean variety on pod number. (F) Effect of bean variety on seed yield. Bars followed by the same letter are not significantly different according to Tukey's HSD test at P ≤ 0.05. ELM3, Test native rhizobia isolate; TC, Consortium of native rhizobia; TB, Commercial inoculant (Biofix); TCB, Biofix combined with consortium; TUC, Negative control (Non-inoculated); ELM, Embu Lower Midland; EUM, Embu Upper Midland; TLM, Tharaka Nithi Lower Midland; TUM, Tharaka Nithi Upper Midland.
Figure 5
Figure 5
Interactive effects of bean variety with farm site on seed yield of climbing beans. Bars followed by the same letter are not significantly different according to Tukey's HSD test at P ≤ 0.05. ELM, Embu Lower Midland; EUM, Embu Upper Midland; TLM, Tharaka Nithi Lower Midland; TUM, Tharaka Nithi Upper Midland.
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