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Phosphite Fertilization for Weed Suppression in PTXD Cotton
Abstract
Herbicide-resistant weeds are a severe problem in cotton production, and new approaches are needed to effectively manage weed resistance. Phosphorus (P) is an essential macronutrient, and plants can only metabolize the orthophosphate (Pi) form of P fertilizer. However, a transgenic variety of cotton expressing the bacterial phosphite dehydrogenase (PtxD) gene can metabolize the reduced form of P i.e. phosphite (Phi), whereas weeds cannot. Therefore, Phi application can be detrimental to weeds in low P soil. The goal of this research was to elucidate the weed control efficacy of Phi under varying levels of residual soil P: very low (10 parts per million [ppm]), low (15 ppm), and moderate (25 ppm). This research was aimed at (1) standardizing the dose of Phi for weed suppression when applied to the soil, (2) determining the optimum dose of Phi as a foliar application, (3) improving the efficacy of glufosinate in tank-mix combinations with Phi, and (4) evaluating the response of different crop and weed species to soil and foliar applications of Phi. In general, Phi application was significantly more effective in 10 and 15 ppm soil P than in 25 ppm soil P. Phosphite applied to the soil resulted in 50-80% growth reduction for Palmer amaranth (Amaranthus palmeri) and up to 40% reduction for johnsongrass (Sorghum halepense) in 10 to 15 ppm soil P. No adverse effect on PtxD cotton was recorded, whereas a significant growth reduction in Coker 312 (wild-type, parental cotton genotype) was observed. Sequential foliar application of Phi at 0.4 kg l-1 incurred >80% injury on broadleaf weeds in 10 and 15 ppm P soils, but grass weeds were impacted to a lesser degree (30-40%). Tank-mixing Phi with glufosinate showed a synergistic effect for the control of Palmer amaranth in 10 ppm soil (40% for glufosinate alone and up to 85% for tank-mix), but the effects were less prominent on johnsongrass. Results show that the Phi-based nutrient management strategy can be an effective tool in the integrated weed management toolbox, especially for the control of broadleaf weed species in soils with low to moderate P levels.
Citation
Singh, Shilpa (2023). Phosphite Fertilization for Weed Suppression in PTXD Cotton. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /198875.