GENETIC IMPROVEMENT OF PERENNIAL FORAGE AND TURF GRASSES FOR THE SOUTHERN UNITED STATES
Location: Crop Germplasm Research
Title: Early-generation germplasm introgression from Sorghum macrospermum into sorghum (S. bicolor)
Submitted to: Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 18, 2009
Publication Date: May 11, 2010
Citation: Kuhlman, L.C., Burson, B.L., Stelly, D.M., Klein, P.E., Klein, R.R., Price, H.J., Rooney, W.L. 2010. Early-generation germplasm introgression from Sorghum macrospermum into sorghum (S. bicolor). Genome. 53:419-429.
Interpretive Summary: Sorghum is an important grain and forage crop that is grown throughout many of the warmer and drier regions of the world. More recently sorghum has shown promise as a bioenergy crop. Improvement of cultivated sorghum has been achieved using different grain sorghum types of the same species or closely related species. However, valuable genetic variation, such as resistance to different insects and diseases, exists in wild grassy sorghum types that are distantly related to cultivated sorghum. Unfortunately this resistance has not been accessed because of difficulties in producing hybrids between cultivated sorghum and the wild grassy sorghums. We were successful in producing hybrids between grain sorghum and one of the wild grassy types (Sorghum macrospermum), and we determined that the transfer of these valuable traits from the wild species to cultivated sorghum through wide hybridization is a viable approach for improvement. We recently crossed one of the above mentioned F1 hybrids with cultivated sorghum and produced backcross hybrids. Then we crossed these backcross hybrids with cultivated sorghum again and were successful in recovering another generation of hybrids. These backcross hybrids were studied using molecular and cytological tools and it was determined that segments of the two species' chromosomes had interchanged which demonstrates that traits can be transferred from the wild grassy sorghum types to cultivated sorghum. This is significant because this work may result in the development of new cultivated sorghum types with more disease and insect resistance which will enhance grain and forage production.
Most genetic improvements of sorghum (S. bicolor [L.] Moench) have resulted from public and private breeding efforts reliant on intra-specific crosses. Recent inter-specific hybridization of the Australian species S. macrospermum and S. bicolor and the definition of their respective genomic relationships AAB1B1YYZZ (2n=4x=40) versus AAB1B1 (2n=2x=20), suggested such crosses might be used for breeding. However, direct uses in sorghum improvement would require genetic recombination and introgression into the S. bicolor genome. We report here on these topics for early-generation backcross hybrids. Fifteen BC1F1 progeny were recovered using the interspecific hybrid as a female and embryo rescue. In these progeny, chromosome numbers ranged from 35 – 70 and all were essentially male sterile. Repeated backcrossing with S. bicolor pollen, produced BC2F1 seed on 3 of the 15 BC1F1 plants. BC2F1 progeny had varying levels of male fertility; selfed seed set ranged from 0 – 95% with only 2 being completely male sterile. Using AFLP and SSR markers, genomic introgression of S. macrospermum ranged from 0 – 18.6%. Cytogenetic analysis revealed chromosome numbers were 20, except for a single backcross with 21 chromosomes. Molecular cytogenetic analysis of BC2F1s confirmed the presence of recombinant introgression chromosomes as well as alien addition and alien substitution chromosomes.