Selection and evaluation of nitrate-tolerant strains of Rhizobium leguminosarum biovar viceae specific to the lentil

Abstract

Seventeen strains of Rhizobium leguminosarum biovar viceae specific to the lentil (Lens culinaris L.) were screened, using the high-yielding lentil cultivar L 4076, for their tolerance to three levels of NO inf3 sup- : 0, 4, and 8 mM NO inf3 sup- . Preliminary screening of this symbiosis for nodulation and N fixation in the presence of NO inf3 sup- showed significant variations among the strains. The number of nodules decreased and nitrogenase activity was depressed in all strains in the presence of NO inf3 sup- . Strains L-1-87, L-27-89, L-33-89, and L-40-89 tolerated 8 mM NO inf3 sup- . Four strains, three tolerant of NO inf3 sup- (L-1-87, L-27-89, and L-33-89), and one sensitive (L-11-89) to NO inf3 sup- , were selected from preliminary screening and used in a pot experiment to assess the symbiosis in the presence of 6 mM NO inf3 sup- at three stages of plant growth, viz., 40 days, 60 days, and at the final harvest. In general, the weight of nodules and C2H2 reduction activity was significantly higher after 60 days than after 40 days. Inoculation with strain L-1-87 produced the maximum number of nodules, and root and shoot biomass both in the presence and the absence of NO inf3 sup- . Nitrate reductase activity in the tops and nodules was assayed only after 60 days and did not show significant variations among strains and NO inf3 sup- treatments. The grain yields for all strains except L-11-89 were significantly higher in the presence of NO inf3 sup- than in the absence of NO inf3 sup- , indicating that tolerant strains contributed symbiotically fixed N to the plant's N pool, resulting in an additive effect on yield. Inoculation with strain L-1-87 produced the maximum grain yield and this strain appears to have potential use as an inoculant in the presence of high levels of soil N.