Seed Nutrition and Quality, Seed Coat Boron and Lignin Are Influenced by Delayed Harvest in Exotically-Derived Soybean Breeding Lines under High Heat

Abstract

The timing of harvest is a major factor affecting seed quality in soybean, particularly in Midsouthern USA, when rain during harvest period is not uncommon. The objective of this research was to evaluate the effects of time of harvest on soybean seed quality (seed composition, germination, seed coat boron, and lignin) in high germinability (HG) breeding lines (50% exotic) developed under high heat. The hypothesis was that seeds of HG lines possess physiological and genetic traits for a better seed quality at harvest maturity and delayed harvest. A 2-year field experiment was conducted under irrigated conditions. Results showed that, at harvest maturity, the exotic HG lines had higher seed protein, oleic acid, sugars, seed coat boron, and seed coat lignin, but lower seed oil compared with the non-exotic checks (Control), confirming our hypothesis. At 28 days after harvest maturity (delayed harvest), the content of seed protein, oleic acid, sugars, seed coat boron, and seed coat lignin were higher in some of the HG lines compared with the checks, indicating a possible involvement of these seed constituents, especially seed coat boron and seed coat lignin, in maintaining seed coat integrity and protecting seed coat against physical damage. Highly significant positive correlations were found between germination and seed protein, oleic acid, sugars, and seed coat boron and seed coat lignin. Highly significant negative correlation was found between germination and oil, linoleic acid, seed coat wrinkling, shattering, and hard seed. Yields of some HG lines were competitive with checks. This research demonstrated that time of harvesting is an important factor influencing seed protein and oil production. Also, since high oleic acid is desirable for oxidative stability, shelf-life and biodiesel properties, using HG lines could positively influence these important traits. This result should suggest to breeders of some of the advantages of selecting for high seed coat boron and lignin, and inform growers of the importance of timely harvest for maintaining high seed quality.

Keywords: boron; lignin; seed coat; seed nutrition; seed oil; seed protein; seed quality; soybean germinability.

Figure 1

Effect of delayed harvest on seed protein, oil, and oleic acid (%) at harvest maturity (A), 14 days after harvest maturity (B), and 28 days after harvest maturity (C); and effect of delayed harvest on germination and accelerated aging (%) at harvest maturity (D), 14 days after harvest maturity (E), and 28 days after harvest maturity (F). Comparison was made between exotic breeding lines and exotic accessions vs. non-exotic checks (Control): genotypic backgrounds comparison. ^* Means there is a significant difference at P ≤ 0.05 between similar color bars in each graph. Bars are mean values ± SE. We used the term “harvest maturity” to refer to the time of harvest shortly after full maturity (R8). The experiment was conducted in 2010 and 2011 in Stoneville, MS, USA.

Figure 2

Effect of delayed harvest on total seed boron (TB, mg kg⁻¹), seed coat boron (SCB, mg kg⁻¹), and seed sucrose (mg g⁻¹) at harvest maturity (A), 14 days after harvest maturity (C), and 28 days after harvest maturity (E); and effect of delayed harvest on seed coat lignin [(mg thioglycolic acid (LTGA) g dwt⁻¹), seed glucose (mg g⁻¹), and seed fructose (mg g⁻¹) at harvest maturity (B), 14 days after harvest maturity (D), and 28 days after harvest maturity (F). Comparison was made between exotic breeding lines and exotic accessions vs. non-exotic checks (Control): genotypic backgrounds comparison. ^* Means there is a significant difference at P ≤ 0.05 between similar color bars in each graph. Bars are mean values ± SE. We used the term “harvest maturity” to refer to the time of harvest shortly after full maturity (R8). The experiment was conducted in 2010 and 2011 in Stoneville, MS, USA.

Figure 3

Air temperature (°C) and rainfall (mm) during the growing season in 2010 (A) and 2011 (B). The experiment was conducted in 2010 and 2011 in Stoneville, MS, USA.