Genetics and Breeding for Glandless Upland Cotton With Improved Yield Potential and Disease Resistance: A Review

Glandless cotton (devoid of toxic gossypol) can be grown as a triple-purpose crop for fiber, feeds, and food (as an oil and protein source). However, its sensitivity to insect pests and its low yield due to the lack of breeding activities has prevented the realization of its potential in commercial seed production and utilization. Since the mid-1990s, the commercialization of bollworm and budworm resistant Bt cotton and the eradication of boll weevils and pink bollworms have provided an opportunity to revitalize glandless cotton production in the United States. The objectives of this study were to review the current status of genetics and breeding for glandless cotton, with a focus on the progress in breeding for glandless Upland cotton in New Mexico, United States. Because there existed a 10–20% yield gap between the best existing glandless germplasm and commercial Upland cultivars, the breeding of glandless Upland cultivars with improved yield and disease resistance was initiated at the New Mexico State University more than a decade ago. As a result, three glandless Upland cultivars, i.e., long-staple Acala 1517-18 GLS, medium staple NuMex COT 15 GLS, and NuMex COT 17 GLS with Fusarium wilt race 4 resistance were released. However, to compete with the current commercial glanded cotton, more breeding efforts are urgently needed to introduce different glandless traits (natural mutations, transgenic or genome-editing) into elite cotton backgrounds with high yields and desirable fiber quality.

Somatic Embryogenesis and Plant Regeneration via Solid-liquid Alternating Culture in Elite Genotypes of Upland Cotton

Background: Cotton is one of the most genotype-dependent plants for regeneration, in order to expand cotton regeneration genotypes and establish efficient regeneration system platform, Jiwu 2031 (glandless cotton), ND 58 and CAU 102, were selected for studying the highly efficient somatic embryos formation and regeneration via solid-liquid alternating culture system.Results: In present research, the MSB medium (MS salts adding B5 vitamins) containing 0.571 µM indole-3-acetic acid (IAA), 0.465 µM kinetin (KT) and 0.904 µM 2, 4-dichlorophenoxyacetic acid (2, 4-D) was effective for callus initiation of fourteen Upland cotton with ‘Corker 201’ as the control. ‘Jiwu 2031’, ‘ND 58’ and ‘CAU 102’ could form somatic embryos and regenerate fertile plants in a solid MSB medium containing 10.31 mM NH4NO3, and supplemented with 0.027 mM glycin, 2.460 µM indole-3-acetic acid (IBA), 0.930 µM KT, 3.784 mM asparagine and 6.843 mM glutamine. Under the solid-liquid alternating culture system, the non-embryonic callus was induced to form embryonic callus and the identical status somatic embryos were obtained in 42 days, and the period for plants regeneration was shortened to 90~120 days, with the higher proportion of normal plant regeneration.Conclusions: The solid-liquid alternating culture method could increase the rate of embryogenesis and shorten the period of plants regeneration of Upland cotton. This work provides the evidence that the glandless cotton is beneficial for somatic embryogenesis (SE) and plant regeneration.