The speed breeding technology of five generations per year in cotton.

Developed a speed breeding technique for cotton that enables up to five generations per year using optimized spectral conditions and immature embryo culture, and created new materials with iaaM gene. Shortening the breeding cycle is an effective way to accelerate crop genetic improvement. Previously we developed an integrated breeding technology for cotton that enabled three to four breeding cycles per year. Here, to further shorten the breeding time, we optimized the light spectrum conditions for cotton development and culture conditions for immature embryo developing into seedling. Under optimized spectrum conditions, JSh929 and ND601 plants exhibited the visible flower buds at 19 and 21 days after emergence (DAE), and the first flower bloomed at around 45 and 46 DAE. Using the optimized immature embryo culture technique, immature embryos of 25-30 days after pollination could develop into fertile plants with cotyledon unfolding at 6 days after culture in vitro. The improved speed breeding technique shortened cotton breeding cycle from about 130 days to a range from 71 to 85 days, an average of 79.5 days, achieving up to around five generations per year. Using this optimized system, we transferred iaaM gene into the high-yield and disease-resistant cultivar JND24, and BCF progenies were obtained within 1.5 years. In addition, the JND24-i3 line was selected with increased lint percentage and improved Micronaire value. These results demonstrate that the optimized speed breeding system offers a rapid and effective way to improve traits of cotton.