Nitrogen Fixation Under Drought of Soybean Genotypes Differing In Ureide Concentration.

Nitrogen fixation in soybean is more sensitive to water stress than other physiological processes such as transpiration. Under drought stress, there is a possible feedback mechanism triggered by the accumulation of the main products of the nitrogen fixation, the ureides, which may decrease nitrogen fixation. Genotypes with low ureide concentration may be able to prolong nitrogen fixation under drought. We created an F₅ derived recombinant inbred population between Jackson (low ureide) and KS4895 (high ureide). These recombinant inbred lines (RILs) were phenotyped for ureide concentration and then genotyped using 195 polymorphic simple sequence markers (SSRs). Five potential quantitative trait loci (QTL) associated with ureide concentration were found in four different linkage groups. Using the molecular marker data, we identified four RILs that were heterozygous at one of the five loci associated with ureide concentration, and by self pollination we obtained four pairs of near isolines (NILs). We conducted a growth chamber experiment to determine if the difference in only one QTL affected ureide concentration within the NIL pairs. Only one out of the four pairs showed a difference in ureide concentration (p<0.05). That NIL pair was included in a field experiment. Also included were 12 RILs that have four or five of the alleles associated with either low or high ureide concentration. We are conducting a field experiment at Fayetteville, Arkansas measuring ureide concentration as well as nitrogen fixation under well watered and drought conditions among the different genotypes.