Date of Award:

1991

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Advisor/Chair:

David W. James

Abstract

Three greenhouse experiments were conducted with three phenotypes of alfalfa (Medicago sativa L.) obtained from a potassium (K)-deficient field and with their diallel crosses grown on low K soil. The first experiment was conduc ted to study the partitioning and broad-sense heritability of K a nd sodium (Na) between leaves and stems of the three phenotypes which were deficient in K and exhibited normal (N), marginal chlorotic (M), and white spot chlorotic (W) leaflets. The second experiment was conducted to study the partitioning of K and Na in leaves, stems, and roots as influenced by 32 alfalfa crosses obtained from diallel crossing of the mother plants of the three phenotypes. The objectives of the third experiment were to study the effects and interactions of nine alfalfa crosses and three soil K and Na levels on transpiration, biomass, and elemental composition of alfalfa components.

The three phenotypes showed no variations in their leaf and stem K concentrations but varied in their ability to partition Na between the leaves and stems. Phenotype M accumulated more Na compared to N and W phenotypes. The Na trait was highly heritable in the broad sense.

The K and Na concentrations varied among the diallel crosses. Crosses with M as the maternal parent had high Na concentrations in leaves while stems and roots accumulated lesser amounts. In contrast, the remaining crosses had higher Na concentrations in roots and lower and least amounts in stems and leaves, respectively.

Significant genetic variation among alfalfa crosses from a single cultivar was observed for transpiration, biomass production, plant water-use efficiency, elemental concentrations, and K utilization efficiency. Leaf and stem biomass and K concentrations in alfalfa components increased in response to increasing soil K levels. The Na concentrations in stems and roots fell in response to increasing soil K levels and increased in response to Na application. The K utilization efficiency of alfalfa increased with increase in soil Na levels, indicating partial Na substitution for K.

The differences among alfalfa phenotypes and crosses from a single cultivar in their Na accumulation and translocation were thought to be governed by plant genetics rather than the direct effect of K availability.

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