Cytogenetics and fertility of an induced tetraploid Sorghum bicolor x S. propinquum hybrid

Development of perennial alternatives to annual crops can alleviate some of agriculture's challenges. Perennial sorghum has the potential of being a low maintenance, drought tolerant, high yielding forage or bioenergy crop. Sorghum bicolor (L.) Moench (ATx623, CMS line) was crossed with S. propinquum (Kunth) Hitchc., and several diploid F 1 hybrids were recovered. One hybrid was treated with colchicine to produce novel tetraploids. A single tetraploid plant was recovered and is the first reported induced tetraploid S. bicolor x S. propinquum hybrid. The fertility and chromosome pairing of this tetraploid hybrid, diploid F 2 hybrids, and both parents were investigated. Pollen stainability for S. bicolor (BTx623, restorer line), S. propinquum , and the F 2 hybrids ranged from 85 to 90%, but stainability was lower (57%) for the induced tetraploid hybrid. Mean seed set of both parents was 65–67% but was 43% for the induced tetraploid hybrid. Meiotic chromosome pairing at metaphase I in both diploid (2n = 2x = 20) parents and the diploid hybrids was primarily 10 bivalents, but the hybrids had a higher frequency of univalents than either parent indicating small chromosomal differences exist between the two species. Mean meiotic chromosome pairing in the induced tetraploid hybrid (2n = 4x = 40) was 0.45 univalents 17.77 bivalents, 0.02 trivalents, and 0.98 quadrivalents per cell. These findings corroborate previous reports that S. bicolor and S. propinquum have a homologous genome.