Selection and Initial Characterization of Partially Nitrate Tolerant Nodulation Mutants of Soybean

Abstract

Since N03-availability in the rooting medium seriously limits symbiotic N2 fixation by soybean (Glycine max [L.] Merr.), studies were initiated to select nodulation mutants which were more tolerant to N03-and were adapted to the Midwest area of the United States. Three independent mutants were selected in the M2 generation from ethyl methanesulfonate or N-nitroso-N-methylurea mutagenized Williams seed. All three mutants (designated NODI-3, NOD2-4, and NOD3-7) were more extensively nodulated (427 to 770 nodules plant-1) than the Williams parent (187 nodules plant1) under zero-N growth conditions. This Since the nts mutants selected by Gresshofls group were derived from the cultivar Bragg which is a Maturity Group VII line and cannot be grown to maturity under Midwest growing conditions, the current study was initiated to select nodulation mutants from a background which can be field tested in the major Midwest soybean production area. This paper provides the initial characterization of three soybean lines with enhanced nodulation capability which were selected from mutagenized populations of Williams (Maturity Group III). MATERIALS AND METHODS Plant MaterialSoybean (Glycine max [L.] Merr., cv Williams) seeds were mutagenized with EMS or NMU as previously described (17). In brief, the four mutagen-treatments (two chemicals and two postwash intervals) consisted of presoaking all seed for 16 h in vigorously aerated water, then treating separate seed lots for 2 h with 50 mM EMS or 5 h with 2.5 mm NMU, followed by either 5-or 9-h postwashes. The mutagenized seed (designated M,) was planted in the field and, at maturity, the four M2 seed lots were individually bulk harvested. The M2 seed lots were then screened for nodulation mutants either in the field or in greenhouse gravel beds.

Shoot versus Root Signal Involvement in Nodulation and Vegetative Growth in Wild-Type and Hypernodulating Soybean Genotypes

“…To further decrease transpiration, the growth chamber was programmed to be dark at 20°C and 80% RH for 12 h followed by half-light intensity for 12 h, and then returned to the normal growth conditions. The plants were watered with a modified nutrient solution (Gremaud and Harper, 1989) supplemented with 1 miv urea-nitrogen as needed. Plants were harvested 21 d after inoculation and nodulation and growth were examined.…”

“…Five days after grafting, the graft union was sufficiently strong to allow transfer of plants. Plants were then transplanted to 2-L polystyrene pots containing a modified nutrient solution (Gremaud and Harper, 1989) supplemented with 1 miv urea-nitrogen. The nutrient solution was changed weekly and pH was maintained at 6.8 2 0.5 with Amberlite IRC-50 resin in a recirculating ion-exchange column, which also served to aerate the solution (Nicholas and Harper, 1976).…”

“…The biochemical nature, the biosynthetic site(s), and the pathway by which the signals are transported and function are unknown. Wedgegrafting studies with most legume nodulation mutants and their respective wild-type parents have demonstrated that it is the shoot that determines the root nodulation phenotype, which suggests that the shoot is the source of the proposed SDI (Delves et al, 1986(Delves et al, , 1987Gremaud and Harper, 1989;Francisco and Akao, 1993;Hamaguchi et al, 1993). Recently, by wedge-and approach-grafting with different shoots (with or without cotyledons and with or without primary leaves) and by nodulation of rooted leaf cuttings, Francisco and Harper (199513) clearly demonstrated that the leaf autoregulates the number of nodules in soybean plants, which confirmed a report by Delves et al (1992).…”

“…Soybean cv Williams 82 and its hypernodulating mutant (NOD1-3) were used in a11 experiments in this study. The hypernodulating mutant was derived from Williams through N-nitroso-N-methylurea mutagenesis and produces at least two to four times the nodule number as on roots of the wild-type parent under similar growth conditions (Gremaud and Harper, 1989;Francisco and Harper, 1995b). Experiments were repeated and data presented are from representative experiments.…”

Effect of Waterlogging During Vegetative Stage On Growth And Yield in Supernodulating Soybean Cultivar Sakukei 4

“…Genetic improvement of symbiotic N fixation is one option for enhancement of the capability of N absorption. Several supernodulating soybean lines that form many more nodules than normally-nodulating cultivars have been isolated through attempts to induce mutations in nodulation capabilities (Carroll et al, 1985a, b;Day et al, 1986;Gremaud and Harper, 1989;Akao and Kouchi, 1992). Most supernodulating lines bred so far, however, showed inferior growth and yield performance compared to their related normallynodulating parental cultivars.…”