Differences in symbiotic N-2 fixation of alfalfa, Medicago sativa L. cultivars and Sinorhizobium spp. strains in field conditions

Abstract

In a two-year field trial, four alfalfa cultivars grown in all combinations with five strains of Sinorhizobium spp. were assessed for N-2-fixing potential and compatibility of symbionts with the aim to co-select plant and rhizobia as alternative approach to symbiotic N-2 fixation improvement. It was found that rhizobial strains, host cultivars and interactions between them had a highly significant effects on shoot dry weight (SDW), total and fixed N content of alfalfa. A significant variation in N-2 fixation effectiveness of rhizobial strains, from ineffective to significantly effective depending on cultivars and year of utilization was detected. Effective strains increased SDW by 49-114% (2010) and 35-86% (2011). In the first year the highest effectiveness had strain L5 with cultivars K-28 and BL-88 and strain L3Si with BL-88 while in the following year all applied strains were effective with different extent. Only one strain (L5) was effective with most of alfalfa cultivars over a two-year period. Percentage of N-2 fixed in plant mass for strain L5 was 33% in 2010, and 38% in 2011. In addition, one cultivar (BL-88) was identified to have superior symbiotic performances, exhibiting its high capacity for N-2 fixation. Results indicate that simultaneous selection of both symbionts should be applied for improvement of N-2 fixation in alfalfa.