Symbiotic effectiveness of pea-rhizobia associations and the implications for farming systems in the western Loess Plateau, China
Interactions between pea (Pisum sativa L.) cultivars and Rhizobium strain affect the symbiotic relationship and ultimately both the nitrogen fixing capacity and the yield. Since Pisum sativum L. is poorly nodulated in the Loess Plateau of China where this crop is grown, the response of pea cultivars Yannong No.2 and Luwan to inoculation with reference Rhizobium ACCC16101, ACCC16103 and selected strains, namely SY3.1, SY12, GWW16, GWC7.3, GDB27, GQW28, GQZ5, GLC1, QGW19 and XC3.1, was studied in two soil types in a greenhouse. Selected strains were isolated from the root nodules of pea (Pisum sativum L.), broad bean (Vicia faba L.) and lentil (Lens culinaris L.) plants in the Loess Plateau of China. Analyses focused on the nodule number, nodule dry weight, plant dry weight, nitrogenase activity, total N accumulation of per plant and seed yield. A significant interaction between pea and rhizobia was observed. The selected strain GDB27 was considered to be the best symbiotically efficient for all pea cultivars in the various soils. Strain XC3.1 evidenced relatively superior symbiotic effectiveness with pea cultivar Yannong No.2. Strains QGW19 and GWW16 performed well with Luwan. Correlation among the parameters for the plants showed that N2-fixation was positively and strongly correlated with nodule dry weight, whole plant dry weight and Acetylene Reduction Assay (ARA) in both soils, but not always significantly correlated with nodule number. Yield increases will follow widespread adoption of inoculation with cultivar-specific strains of Rhizobium.
Key words: Nitrogen fixation, Rhizobium, Loess Plateau, soil type, yield increase