INHERITANCE OF POTASSIUM-SODIUM NUTRITIONAL TRAITS IN ALFALFA

Alfalfa (Medicago sativa L.) growing on K-depleted, semiarid, calcareo us soil displays three K-deficiency symptoms: (i) white spots on leafl ets (W), (ii) marginal chlorosis (M), and (iii) normal leaflets on stu nted plants (N). In a greenhouse study, we examined partitioning and h eritability of K and Na nutritional traits in three alfalfa clones and their crosses, and also how K and Na soil fertility levels affected b iomass production, genetic dependence of K and Na uptake and partition ing, and K use efficiency. Mother plants were propagated vegetatively and by seed from phenotype crosses in a low-K, low-Na, calcareous soil rooting medium. One trial used K- and Na-amended soil. Harvests were at early bloom. Leaves contained more K than stems, with no difference among phenotypes; Na was uniform in stems, but leaves of M contained much more Na than leaves of N and W. With nonamended soil, K and Na up take and partitioning among leaves, stems, and roots were significantl y affected by cross. The Na:K ratio in leaves, stems, and roots was st rongly influenced by phenotype and cross. Biomass production of leaves and stems differed among crosses and was increased by K fertilization ; Na fertilization affected biomass only of leaves, and only in crosse s MxM and NxN (Na may have partially replaced K). The shoot:root ratio was affected only by cross. Potassium use efficiency was affected by cross and by Na fertilization. Broad-sense heritability for K and Na c oncentration was high, especially for Na in leaves and stems. Uptake a nd partitioning of Na and K in phenotype crosses supported narrow-sens e heritability as well. Genetics, rather than soil K-Na competition, g overned Na uptake, translocation, and utilization by phenotypes. Accor dingly, characterization of K nutrition in alfalfa must consider Na le vels. As phenotypes of alfalfa cultivars range widely in K-Na nutritio nal traits, it should be possible to select for high yield and K use e fficiency.