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

Commercial recombinant DNA technology (GM traits) within cotton (Gossypium hirsutum) cultivars has been rapidly and widely adopted across multiple cotton producing countries. Glyphosate herbicide resistance (GHR) is the prominent technology and is often stacked with other GM traits. GM traits carry patents and have changed the legal structure of all major cotton breeding programs around the world. Cross pollination can readily transfer GM 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 indeterminate growth habit. Volunteer plants and inadvertent mechanical mixture during seed processing are other potential sources of contamination. Currently GM traits do no alter the natural phenotype of the cotton plant; thus, adventitious presence (AP) can only be confirmed with expensive molecular analyses. A field method to phenotypically identify GM trait carrying plants would be a great tool to help manage AP in early generation breeding nurseries. Trials were conducted at Lubbock, TX in 2013 and 2014 to evaluate potential use of low-rate broadcast glyphosate treatments to induce identifying phenotypic differences between cotton plants “GHR +” and “GHR –“ 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. Plots were arranged in a 3²X5 factorial design with three factors for seed mixture and application timing and five factors for herbicide rate. Plots were evaluated after glyphosate application for incidence of herbicide damaged plants. Damaged and non-damaged plants were tested for GHR trait presence. Incidence ratings were compared to actual trait presence numbers. Boll number, yield, and multiple seed quality parameters were evaluated.