Date of Graduation

12-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Chen, Pengyin

Committee Member

Brye, Kristofor R.

Second Committee Member

Clark, John R.

Third Committee Member

Mauromoustakos, Andronikos T.

Fourth Committee Member

Oosterhuis, Derrick M.

Keywords

Biological sciences; Phytate; Seed composition; Soybeans; Stachyose

Abstract

The development of cultivars with modified seed composition represents an excellent alternative to cope with the world's need for more nutritious food. Understanding the genetic and environmental factors controlling crop seed quality traits is of crucial importance for such an endeavor. The objectives of this study were: a) to evaluate the efficiency of phenotype and marker-assisted selection for low stachyose and low phytate soybean breeding lines, and their yield stability, b) to study the effect of management practices planting date and delayed harvest on soybean seed composition, and c) to study the potential association between soil properties and leaf chemical element concentration, with seed composition. Selection efficiency in six breeding populations segregating for the low phytate and low stachyose traits was studied by determining the proportion of phenotypically selected lines that carried the alleles for the low phytate trait or low stachyose traits. Yield stability of low phytate/low stachyose lines was studied in a set of 16 breeding lines selected from a breeding population segregating for the low phytate/low stachyose trait, and grown in five Arkansas environments. Planting date effects on seed composition were studied in nine breeding lines planted in early May, late May, and late June at two Arkansas locations in two consecutive years. Delayed harvest effects on seed composition and the association between soil properties and leaf chemical element concentration, with seed composition were studied in the late May planting date. Results showed that the efficiency of marker-assisted selection depended on the type of marker used, whereas phenotype-assisted selection depended on the germplasm that was being screened and on the phenotype used to make breeding selections. Breeders should use marker-assisted selection for low phytate/low stachyose lines only if phenotyping large number of progenies is not time or cost effective. Most of the low phytate/low stachyose lines showed low yield stability. However, one of the low phytate/low stachyose lines studied, R08-6009, showed competitive yield and adaptation to all the environments where the line was evaluated. R08-6009 should be crossed to high-yield lines to generate progeny with greater yield potential. Other lines studied showed moderately high oleic (>45 mg g-1) and low linolenic (g-1) acids concentrations in the oil, which are novel and unique combinations with the low phytate/low stachyose trait. Planting date significantly affected seed organic and inorganic composition. Early planting increased seed protein, oleic acid and decreased linolenic acid, whereas late planting increased sucrose, but did not affect stachyose. Production of soybeans with high protein/high quality oil should be performed in early-planting production systems, whereas planting high sugar food-grade cultivars late in the season should fit well in a double-crop system. Although seed components tended to decrease when harvest was delayed, the magnitude was not large enough to recommend to purposely change the time of harvest to attain a particular seed composition (e.g. low seed calcium). Attempting to modify composition by nutrient fertilization may not be profitable, as no association between leaf or soil chemical elements with seed composition was observed. The findings reported in this dissertation may help: 1) develop low phytate/low stachyose soybean breeding lines/cultivar adapted to Arkansas, 2) understand how those breeding lines can be developed in a shorter period of time (increase selection efficiency), 3) deliver specialty soybean cultivars that come not only come with improved seed quality traits and high yield potential, but also with supporting information on some management practices (planting date, time of harvest, response to specific soil nutrients) that may help farmers meet market specifications and contribute to sustainable agriculture.

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