Seed nutrition and quality, seed coat boron and lignin are influenced by delayed harvest in exotically-derived soybean breeding lines under high heat

Authors: Bellaloui, Nacer; Smith, James - Rusty; Mengistu, Alemu

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2017
Publication Date: 9/22/2017
Citation: Bellaloui, N., Smith, J.R., Mengistu, A. 2017. Seed nutrition and quality, seed coat boron and lignin are influenced by delayed harvest in exotically-derived soybean breeding lines under high heat. Frontiers in Plant Science. 8:1-16. https://doi.org/10.3389/fpls.2017.01563.
DOI: https://doi.org/10.3389/fpls.2017.01563

Interpretive Summary: Producing soybean under high heat conditions of the Midsouth, especially in the Mississippi Delta, leads to poor seed quality. The poor seed quality could be due to high heat, high humidity, and delayed harvest due to rain during harvest. Therefore, developing high heat tolerant soybeans that produce high seed quality (high germination rate, vigor, yield, and desirable high seed composition constituents such as seed protein, oil, fatty acid, and sugars) are a major goal of soybean breeders and seed industry. The objective of the current research was to evaluate the responses of exotically-derived soybean breeding lines having good germination under high heat conditions and investigate the effects of delayed harvest on soybean seed quality, seed coat boron, and seed coat lignin. This is to understand the physiological and genetic traits related to heat tolerance and seed quality. A two-year field experiment was conducted under irrigated conditions. Six exotic breeding lines with high germination rates and six checks were used. Results showed that, at harvest maturity, the exotic high germination breeding lines had high seed protein, oleic acid, sugars, seed coat boron, and seed coat lignin, but lower seed oil compared with checks. Also, some exotic breeding lines had competitive yield with checks. At 28 days after harvest maturity (delayed harvest), although the seed constituents declined in exotic breeding lines, they maintained high levels of seed constituents, including seed coat boron and seed coat lignin, indicating a possible involvement of these constituents in seed coat integrity and seed coat protection against physical damage. High germination was associated with high levels of seed protein, oleic acid, sugars, and seed coat boron and seed coat lignin. High germination was associated with low levels of oil, linoleic acid, wrinkling, shaterring, and hard seed. This research demonstrated that time of harvesting should be considered for higher seed protein and oil production, and for producing seeds with high quality. Since high oleic is desirable for oxidation stability of shelf-life and biodiesel properties, high germinability breeding lines have potential benefit and production gain. The information is beneficial to breeders to select for high seed coat boron and lignin, and to growers to select for high seed protein or oil production.

Technical Abstract: Growing heat sensitive soybean under the high heat and humid environment of the Early Soybean Production System (ESPS) in the Midsouthern USA often leads to poor seed quality. Therefore, breeding for heat tolerant soybeans that maintain high quality of seed nutrition, high germination, and high protein and oil production is one of our major breeding goals. Under ESPS conditions, where rain during harvest is not uncommon, timing of soybean harvest is a major factor affecting seed quality. Therefore, the objective of this research was to evaluate the effects of time of harvest on soybean seed quality components (seed composition, seed germination, seed coat boron, and seed coat lignin) in high germinability (HG) breeding lines (50% exotic) developed under high heat. Our hypothesis was that seeds of HG lines possess physiological and genetic traits for high seed germinability at delayed harvesting. Two-year field experiment was conducted under irrigated conditions. Four exotic breeding lines and two exotic germplasm accession with high germinability were evaluated with six non-exotic checks. Results showed that, at harvest maturity, the exotic HG lines had high seed protein, oleic acid, sugars, seed coat boron, and seed coat lignin, but lower seed oil compared with checks. 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 HG lines compared with checks, indicating a possible involvement of these seed constituents, especially coat boron and seed coat lignin, in maintaining seed coat integrity and protecting seed coat against physical damage. Highly significant positive correlation (P=0.001) was found between germination and seed protein, oleic acid, sugars, and seed coat boron and seed coat lignin. Highly significant negative correlation (P=0.001) was found between germination and oil, linoleic acid, wrinkling, shattering, and hard seed. Yield of some HG lines was competitive with checks. This research demonstrated that time of harvesting is an important factor influencing seed protein and oil production, and determines seed quality. Also, since high oleic acid is desirable for oxidative stability, shelf-life and biodiesel properties, using HG lines would have production benefit and potential gain for specialty production for high protein and more stable oil. The information should inform breeders of some of the advantages of selecting for high seed coat boron and lignin, and to growers to select for high protein or oil production.