Potential Discovery of 2,4-D Tolerance Among Interspecific Chromosome Substitution Lines of Upland Cotton

Weeds greatly reduce cotton growth, yield, harvest-ability and fiber quality, so their management is crucial to cotton production. Weed management strategies often rely on herbicides, due to their simplicity, ease of application, and effectiveness. However, subsequent to the widespread adoption of glyphosate-resistant crops, numerous herbicide-resistant weeds have evolved. With glyphosate rendered ineffective, growers and companies have searched for novel herbicide resistance genes. Given that most glyphosate-resistant weeds can be controlled with 2,4-dichlorophenoxyacetic acid (2,4-D), we have screened and identified cotton germplasm with novel tolerance against it. Previous studies have identified wild cotton species as a reservoir of novel genetic variations. Unfortunately, the application of conventional varietal breeding methods to interspecific introgression has resulted in little tangible success. An alternative breeding method, chromosome substitution (CS), involves first introgressing interspecific germplasm into an upland cotton genetic background and then screening Upland CS lines to discover novel variants. Here, we report the discovery of a novel Upland cotton germplasm as potential sources of genes for 2,4-D tolerance. A total of 47 CS lines of G. barbadense (CS-B), G. tomentosum (CS-T), and G. mustelinum (CS-M), in the genetic background of Gossypium hirsutum Texas Marker-1 (TM-1) were screened for resistance to a field-recommended rate (1.12 kg ai ha^-1) of 2,4-D in a completely randomized design with sub-sampling (r=3). Injury from 2,4-D applied at 2 weeks after seedling emergence ranged from 25-100% at 21-28 days after treatment (DAT). Five CS lines including CS-T04-15, CS-B12, CS-B15sh, CS-T04, and CS-B22sh exhibited the lowest injury levels, possibly indicating the presences of 2,4-D tolerance gene(s). Field studies to re-test 2,4-D tolerance levels of the five CS lines are currently underway. Findings from this study could help discover novel 2,4-D tolerant cotton germplasm that ultimately improves weed management options in upland cotton cultivation.