With 2 figures and 4 tables
Abstract
We have developed an integrated breeding technology for cotton that can accelerate generation advancement to three or four times per year. This approach includes in vitro culturing of immature embryos into plantlets, which saves time because of no waiting for seed maturation. In addition to selection for kanamycin resistance and PCR identification of the gene of interest (here, insect resistance), we also incorporate methods such as plantlet grafting and growth regulation. In this way, embryos aged 20–30 days postanthesis can develop directly into plantlets in another 10–15 days. Here, kanamycin and PCR selection plantlets were grafted using a new and efficient technique called cotton joint graft, which can provide a reliable survival rate of 90–100%. Growth of the grafted plants was regulated for rapid development by adjusting the soil nutrients. We also treated the pedicels of hybridized or back‐crossed bolls with a mixture of naphthalene acetic acid and gibberellic acid to prevent shedding. Over the course of 1 year, we were able to produce three or four generations at intervals of about 90–120 days, i.e. from immature embryo culture through pollination and fecundation. Using this procedure, we transferred the Cry1Ac gene into three recurrent cultivars, ‘Han93‐2’, ‘Jimian20’ and ‘Nongda94‐7’. This was accomplished through four backcross generations and one cycle of selfing. BC4F2 progenies were obtained within 1.5 years, with each generation being completed between 89.0 and 117.3 days.