Abstract:

Symbiotic compatibility of different rhizobia strains with important Chinese milk vetch （CMV） cultivars was studied to identify rhizobia with a broad host compatibility high nitrogen fixation ability for CMV crop inoculation， with a view to improving CMV nitrogen fixation ability and performance. Eight rhizobia strains isolated from different geographic CMV production regions and eight important CMV cultivars were used in the research. A hydroponic tube test showed six of the eight rhizobia strains could establish good symbiosis with all of the eight tested CMV cultivars. Four rhizobia strains with better symbiosis were re-tested in a vermiculite pot experiment in which the effective nodule number， nodule fresh weight， nitrogenase activity， dry weight， and nitrogen accumulation of CMV were recorded and analyzed. It was found that compared with the uninoculated control， rhizobia inoculation significantly increased the dry weight and nitrogen accumulation of CMV. Across the eight tested CMV cultivars and four rhizobia strains， CMV shoot dry weights were 3.23-7.12 times higher and root dry weights were 1.64-4.12 times higher in inoculated than in uninoculated plants. Similarly， shoot nitrogen accumulation was 12.72-37.84 times higher， and root nitrogen accumulation 5.42-13.63 times higher in inoculated plants than in the control treatment. There were also differences between CMV cultivars and rhizobia strains in nitrogen fixation ability. The eight cultivars tested differed in their response to inoculation. CMV cultivars Yijiangzi and Ningbodaqiao were generally more responsive， and cultivar Xinzi No.1 was generally less responsive. For cultivars Yijiangzi and， Ningbodaqiao， shoot dry weight was 1.78-1.87 times higher； root dry weight was 1.68-1.99 times higher； shoot nitrogen accumulation was 1.14-2.08 times higher and root nitrogen accumulation was 1.74-2.40 times higher than for cultivar Xinzi No. 1. Among the four rhizobia strains re-tested in the pot trial， strain 7653R was superior to the other three （13005， 13025 and 13052）. Averaged over the eight tested CMV cultivars， the effective nodule number was 1.17-1.19 times higher； the nodule fresh weight was 1.15-1.22 times higher， and nitrogenase activity was 1.38-1.45 times higher for rhizobia strain 7653R than for the other 3 strains. ANOVAs for CMV and rhizobia strain effects and their interaction showed that the contribution of rhizobia strains to effective nodule number， nodule fresh weight， nodule dry weight， and nitrogen accumulation was 50.79%-87.64%， compared with a 7.17%-32.83% contribution of CMV cultivars. Symbiotic compatibilities among different rhizobia strains and the main CMV cultivars were elucidated， and these data provide a knowledge base for further screening of rhizobia strains with excellent field performance.

Key words: main Chinese milk vetch cultivars, rhizobia strains, symbiotic compatibility, nitrogen accumulation