GENETIC-VARIATION FOR NITROGEN USE IN SOFT RED X HARD RED WINTER-WHEAT POPULATIONS

Hard red winter (HRW) wheat (Triticum aestivum L. em. Thell.) cultivars are genetically distinct from soft red winter (SRW) wheat cultivars and thus provide new sources of germplasm for SRW wheat breeding programs. Previous research has shown that HRW X SRW wheat crosses can generate segregates with acceptably low grain protein concentration (GPC). This study was conducted to evaluate genetic variation of traits related to N uptake, partitioning, and utilization in HRW X SRW wheat populations. The F3 and F4 generations of three HRW X SRW crosses were grown in 1985 and 1986, respectively, on a Maury silt loam soil (fine, mixed, mesic Typic Paleudalf) near Lexington, KY. Significant differences among F4 families were observed for N harvest index (NHI), GPC and N use efficiency for yield (NUEY) and protein (NUEP) in all populations. The correlation between N partitioning (NHI) and GPC varied among crosses, ranging from r = -0.57 (P < 0.01) to near zero. Highly significant differences for NUEY and NUEP were observed among F4 families of each cross. A path analysis indicated that the direct effect of N uptake efficiency accounted for as much as 91% of the variation in NUEY and 88% in NUEP. Indirect effects were of little consequence. The data demonstrate that N-use traits are strongly influenced by the environment, and would be difficult to modify in a breeding program.