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

Abstract

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 F1 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 F2 hybrids, and both parents were investigated. Pollen stainability for S. bicolor (BTx623, restorer line), S. propinquum, and the F2 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.