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Document Type

Dissertation - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Plant Science

First Advisor

Zeno Wicks III


Experiments were performed to determine whether diurnal osmotic adjustment (DOA) is an effective strategy for improving water stress tolerance of maize and to determine whether it is a selectable trait. Diurnal osmotic adjustment was determined from pre-dawn and midday solute potential (ψcs) corrected for relative water content (RWC) in leaf samples from intact plants: DOA=AM ψcs - PM ψcs. High- and low-DOA populations developed by divergent recurrent phenotypic selection did not have significantly different DOA, except in 1992 when PM samples were collected from detached leaves. The DOA was greater in detached leaves of the cycle-four-high-DOA population than in the cycle-four-low-DOA population. Sampling date, genotype, and sampling date x genotype significantly affected DOA when S3-4 (initiated from the C-1 high- and low-DOA populations) and inbred lines A654 and CM105 were grown with controlled watering. The DOA was lowest during grain fill. Diurnal change in RWC (DRWC) was significantly affected by genotype, sampling date, sampling date x genotype, and the covariate, date of anthesis. Topcrosses and their parents were grown in the field and sampled for DOA, DRWC, and praline level. Pre-dawn samples were collected from intact plants, but PM samples were taken from detached wilted leaves. The DOA varied significantly among parents, but not topcrosses. Time significantly affected ψcs, indicating solute accumulation during wilting of the detached leaves. The DRWC of topcrosses was significantly affected by genotype. Parent-offspring regression was used to estimate narrow-sense heritability (h2): DOA h2=7.37%, DRWC h2=9.98%. Female, but not male, parent significantly affected topcross DRWC. Praline accumulated during wilting of detached leaves. Genotype, time, and genotype x time were all highly significant factors affecting praline level. In another experiment, six genotypes were grown in a growth chamber with well-watered and water-deficient treatments. The DOA varied significantly among genotypes and between watering treatments. Although well-watered plants had greater genotypic mean DOA, water-deficient plants had lower ψcs, indicating long-term OA. Proline levels were significantly affected by genotype x time, genotype x treatment, and genotype x time x treatment.

Library of Congress Subject Headings

Corn -- Drought tolerance
Corn -- Water requirements
Corn -- Genetics
Corn -- Osmotic potential




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