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Heritability and Repeatability of Enhanced N<i>2</i> Fixation in Early and Late Inbreeding Generations of Soybean
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1994
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Plant GeneticsBotanyGeneticsGenomicsCrop ImprovementLate Inbreeding GenerationsBreedingSoil NitrateN 2Soil FertilityLow HeritabilityQuantitative GeneticsAgricultural GeneticsGenetic VariationPopulation GeneticsPlant BreedingBiologyNatural SciencesEvolutionary BiologyCrop ProtectionCrop ScienceMedicine
Moderate to high levels of soil nitrate suppress nodulation and N 2 fixation in soybean [ Glycine max (L.) Merr.], resulting in some instances in a net loss of N from the soil when the high‐protein seed is harvested. Development of nitrate tolerance, i.e., the ability to nodulate and fix N 2 in the presence of soil nitrate, in cultivars of soybean is desirable. Our objectives were to (i) combine, through hybridization, the reported nitrate tolerance of Korean genotypes 464, 466, 468, and 469 (Commonwealth of Australia Plant Introduction nos CPI66126, CPI66141, CPI66157 and CPI66159, respectively) with the agronomic and seed traits of cultivars Valder, Reynolds, Forrest and Bossier; (ii) assess heritability and repeatability of N 2 fixation between individual F 2 plants and F 2 ‐derived F 3 lines, and F 3 ‐derived lines in the F 6 and F 7 generations; and (iii) examine correlations of N 2 fixation with agronomic and seed traits. Individual plants and lines were evaluated during five seasons between 1986–1987 and 1990–1991 on alkaline vertisol soils (Typic Pellustert) at Breeza and Narrabri, Australia, and in glasshouse culture at Narrabri. The xylem ureide technique was used to estimate N 2 fixation activity of individual F 2 plants, and of F 2 ‐derived F 3 lines and F 3 ‐derived F 6 and F 7 lines. Data from F 2 and F 3 generations showed that relative ureide‐N values for the individual F 2 plants was of low heritability. We concluded that single‐plant selection for N 2 fixation in the F 2 generation was largely ineffective. Data from F 6 and F 7 plot trials, however, indicated that repeatability on a plot basis for relative ureide‐N was about 0.5 ( P < 0.01). Phenotypic correlations between relative ureide‐N in xylem sap and other plant and seed traits were variable and generally non‐significant. The selection of site was vital for detecting enhanced N 2 fixation. Sites with low soil nitrate did not allow discrimination among genotypes. Three F 3 ‐derived lines, D22‐8, K78‐1, and A46‐4, which were identified in the F 6 and F 7 trials at the high‐nitrate sites, had the N 2 fixation characteristics of the Korean parents and near‐commercial yields (75–83% of that of the highest yielding cultivar, Forrest.