Visual Field Screening Strategy for Purity and Seed Quality in Conventional Breeding Nurseries

Commercial recombinant DNA technology (GE traits) within cotton (Gossypium hirsutum) cultivars has been rapidly and widely adopted across multiple cotton producing countries. Glyphosate resistance (GR) is the prominent technology in the U.S. and is often stacked with other GE traits. Genetically Engineered traits carry patents and have changed the legal structure of all major cotton breeding programs around the world. Cross pollination can readily transfer GE traits to unlicensed germplasm once a trait is commercialized and no longer under regulated status. Cotton is a self-pollinated crop, in which cross pollination can easily occur, and flowers over a long period due to its perennial growth habit. Volunteer plants and inadvertent mechanical mixture during seed processing are other potential sources of contamination. Currently GE traits do not alter the natural appearance of the plant; thus, adventitious presence (AP) can only be confirmed with expensive molecular analyses. A field method to visually identify GE trait carrying plants would be a beneficial tool to help manage AP in early generation breeding nurseries. Trials were conducted at Lubbock, TX in 2013 and 2014 to evaluate the potential use of low-rate broadcast glyphosate treatments to induce identifying visual differences between cotton plants “GR +” and “GR –“ within a breeding nursery. Three synthetic mixtures were planted: 100% conventional cultivar, 50/50% mixed conventional and Genuity® Roundup Ready® Flex cultivars, and 100% Genuity® Roundup Ready® Flex cultivar. Multiple low rates of glyphosate were applied at multiple timings. 4 rows by 25 foot plots were arranged in a randomized complete block design, and treatments were structured as a 3²X5 factorial. Plants were evaluated after application for incidence of herbicide response. Damaged and non-damaged plants were tested for GR trait presence. Incidence ratings were compared to actual trait presence numbers. Boll counts, yield, and multiple seed quality parameters were evaluated.