Submitted to: Proceedings of Southern Weed Science Society
Publication Type: Proceedings
Publication Acceptance Date: 1/19/2011
Publication Date: 1/25/2011
Citation: Bellaloui, N., Reddy, K.N., Gillen, A.M., Abbas, H.K., Abel, C.A. 2011. Glyphosate and boron application effects on seed composition and seed boron in glyphosate-resistant soybean. Proceedings of Southern Weed Science Society. http://www.swss.ws/NewWebDesign/Meeting/2011%20Meeting/SWSS_2011_Program%20Final.pdf.
Technical Abstract: Soybean seed is a major source of protein and oil in the world. Seed quality is determined by the content of protein and oil. Soybean seed contains five major fatty acids, saturated fatty acids (stearic and palmitic), and unsaturated fatty acids (oleic, linoleic, and linolenic). Both linoleic and linolenic acids are polyunsaturated fatty acids that are easily oxidized which leads to “off-flavors” in food. Therefore, to make soybean oil more stable, producers have traditionally hydrogenated the oil. The hydrogenation process produces trans fatty acids, which are undesirable because of their negative impact on human health. Monounsaturated fatty acids such as oleic acid are less susceptible to oxidation during refining, storage, and frying. Consequently, the food industry is becoming increasingly interested in producing soybean seed with high oleic acid and low linoleic and linolenic acids. Glyphosate (Gly) is a nonselective broad-spectrum herbicide used throughout the world for postemergence weed control. The effect of Gly on cationic nutrients such as Mn2+, Zn2+, Fe3+, K+, and Ca2+ has been previously studied. Results from these studies showed that Gly application decreased Fe, Mn, and Zn concentrations in plant tissues and reduced Gly effectiveness. This is because the cationic nutrients form Gly-cation complexes, leading to inactivation of Gly activity. Literature on the effect of Gly on anionic nutrients such as boric acid is scarce. Boric acid is a weak acid, and in aqueous solution pH<7, it occurs as undissociated boric acid (H3BO3); while at high pH, boric acid accepts hydroxyl ions from water and forms a tetrahedral borate anion B(OH)4-. Boron (B) exists in plants as borate anion (BO3-3), and its involvement in flowering set, seed set, and seed quality is well established. Therefore, the objective of this study was to evaluate the effect of tank-mixing of Gly-B on seed composition and seed B in soybean. A two-year field experiment was conducted in 2006 and 2008 at Stoneville, MS, U.S.A. Glyphosate was applied at a rate of 0.84 kg ha-1 at 4 weeks after planting (WAP) and 8 WAP. The treatments were: control (C), plants that received no Gly and no foliar B; Gly, plants that received Gly alone at 4 WAP and 8 WAP; B, plants that received B alone at 4WAP and 8WAP; and Gly-B, plants that received both Gly and B combined at 4 WAP and 8WAP. The results showed that application of Gly, Gly-B, or B increased seed protein, oleic acid, and total amino acid concentrations in the seed. By contrast, oil and linolenic acid concentrations decreased under those treatments compared with the control. Gly-B combined or B treatment increased B concentration in leaves and seed. The results suggest that Gly-B tank mixing may not antagonize B uptake and translocation to leaves and seed. The results also showed that the inhibitory effect of Gly on nutrient uptake and translocation may depend on the ion species and form of the nutrient mixed with Gly. This research demonstrates that Gly-B application alters seed composition and B status in leaves and seed.