In cotton programs involving haploids or interspecific hybrids, a common bottleneck to progress is the low number of available plants and the recalcitrant nature of the plants to be doubled in chromosome number by colchicine. We have found that cuttings from cotton and cotton interspecific hybrids can be rooted easily by placing them in 2 mg/l NAA in tap water for 2-3 weeks, with light, then transferring the cuttings to tap water alone for an additional 2 weeks. Rooted cuttings on which lateral buds are breaking can be submerged in 1000 ppm colchicine for 15 to 18 hr. to induce chromosome doubling before potting.

When interspecific hybrids are produced by ovule culture, the germinating embryos can be doubled with about 20% efficiency if they are placed on agar containing 50-100 ppm for no more than 8 hr. The most effective concentration and time depends upon the specific hybrid. Mature seeds with seed coat removed can be doubled by germinating them for 1-2 weeks on agar with 8-10 ppm colchicine.