Submitted to: Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2008
Publication Date: 8/22/2008
Citation: Kuhlman, L.C., Burson, B.L., Klein, P.E., Klein, R.R., Stelly, D.M., Price, H.J., Rooney, W.L. 2008. Genetic recombination in Sorghum bicolor x S. macrospermum interspecific hybrids. Genome. 51:749-756.
Interpretive Summary: Sorghum is an important grain and forage crop that is grown throughout many of the warmer and drier regions of the world. Most of the improvement within cultivated sorghum has been achieved within grain sorghum types of the same species or closely related species. However, valuable genetic variation exists that is not being accessed – examples being resistances to different insects and diseases occurring in wild grassy sorghum types that are distantly related to cultivated sorghum. Until recently, breeders could not produce hybrids between cultivated sorghum and the wild grassy sorghums. We recently succeeded in producing hybrids between grain sorghum and one of the wild grassy types (Sorghum macrospermum). We determined that barriers to successful trait transfer to cultivated sorghum exist within the hybrid, but evidence suggests that transfer is possible. This information is important because it indicates that transfer of valuable traits from wild species to cultivated sorghum through the use of hybrids is viable. This work may result in the development of new cultivated sorghum types with more disease and insect resistance and enhanced grain and forage production.
Technical Abstract: Sorghum has been improved by public and private breeding programs utilizing germplasm mostly from within the species Sorghum bicolor. Until recently, cross-incompatibilities have prevented its hybridization with most species within the genus Sorghum. Utilizing germplasm homozygous for the iap allele, hybrids were readily produced between S. bicolor (2n = 20; AAB1B1) and S. macrospermum (2n = 40; WWXXYYZZ). These hybrids were intermediate to the parents in chromosome number (2n = 30) and overall morphology. Meiosis in both parents was regular; S. bicolor had 10 bivalents per pollen mother cell (PMC) and S. macrospermum had an average of 19.89 bivalents per PMC. Six hybrids were studied cytologically and meiosis was irregular with the chromosomes associating primarily as univalents and bivalents. There was an average of 3.54 bivalents per PMC, with a range of 0-8 bivalents, most of which were rods (98%). Using FISH (Fluorescent In Situ Hybridization), moderate levels (2.6 II per PMC) of allosyndetic recombination were observed. Genomic relationships were sufficient to assign S. macrospermum the genomic formula AAB1B1YYZZ, Y and Z remain unknown. Allosyndetic recombination in the interspecific hybrids indicates that introgression through genetic recombination should be possible if viable backcrosses can be recovered.