| Popis: |
Commercial genetically engineered (GE) traits within cotton (Gossypium hirsutum L.) cultivars are rapidly and widely adopted across multiple cotton producing countries. Commercial GE traits up until present, 2017, confer herbicide tolerant (HT) and heliothis insect resistant (IR) phenotypes with genes from species other than Gossypium (transgenic) using recombinant DNA techniques. Glyphosate herbicide resistance (GR) is the predominant technology in the U.S. and is often stacked with other GE traits. Genetically engineered traits are patented, contributing to changes in the legal structure of cotton breeding programs around the world. Commercial GE traits can unintentionally proliferate in cotton breeding germplasm through natural cross pollination, volunteer plants and inadvertent mechanical mixture during seed processing. Genetically engineered traits do not alter the natural appearance of the plant; thus, adventitious presence (AP) can only be confirmed with genetic or molecular analyses. A field method to visually identify transgenic plants in conventional (non-transgenic) breeding germplasm would be a beneficial tool to help manage AP in early generation breeding nurseries. Trials were conducted at Lubbock, TX in 2014 and 2015 to evaluate potential use of low-rate broadcast glyphosate treatments to induce identifying visual differences between GR and glyphosate susceptible (GS) cotton plants within a breeding nursery. Three combinations from phenotypically similar cultivar were planted; 100% GS, 100% GR and a 50% mixture of both. Five rates of glyphosate (0X, 0.25X, 0.5X, 0.75X and 1X of 138 g a.e. ha-1 labeled rate) were applied at three development timings (5 vegetative nodes, 8 vegetative nodes and 11 vegetative nodes). Plants were evaluated seven and 16 days after application for incidence of herbicide response. Damaged and non-damaged plants were tested for GR GE trait presence. Incidence ratings were compared to actual trait presence numbers. Boll counts, yield, fiber and seed quality parameters were evaluated. Most applications negatively impacted yield, especially in 2015 when growing season was shortened due to late planting. When the objective is to advance a breeding generation, and yield is not a concern, 0.5X labeled rate, 69 g a.e. ha-1 applied at fifth vegetative node development stage is the most promising application for visual field screening strategy to remove GE traits from conventional cotton breeding nurseries. |
