Submitted to: Australian Journal of Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/26/2005
Publication Date: 9/30/2005
Citation: Price, H.J., Hodnett, G.L., Burson, B.L., Dillon, S.L., Rooney, W.L. 2005. A Sorghum bicolor x S. macrospermum hybrid recovered by embryo rescue and culture. Australian Journal of Botany. 53:579-582. Interpretive Summary: Cultivated sorghum has some grassy wild relatives that are of interest to both sorghum and grass breeders. The reason for the interest in these wild relatives is that some of them are not attacked by insects and diseases that frequently attack sorghum and reduce grain yields. Most of these wild relatives are grassy forage plants and there is also interest in using them to develop better forage sorghums. However, to develop sorghum with more insect and disease resistance or an improved forage type, these wild relatives will have to be crossed with cultivated sorghum to produce hybrids. Unfortunately, no one has been able to successfully cross the wild relatives with cultivated sorghum. In this study we were able to produce and recover a hybrid between grain sorghum and one of the wild species. This is the first time a hybrid of this type has been produced. This paper describes the new hybrid and compares it to both of its parents. This hybrid is the first step in using the grassy wild sorghum species in the potential improvement of cultivated sorghum.
Technical Abstract: While exotic germplasm is extensively used in sorghum improvement programs, Sorghum species classified in sections other than Eu-sorghum have not been utilized as germplasm because of strong reproductive barriers involving pollen-pistil incompatibilities. Sorghum macrospermum is of particular interest to sorghum breeders because of its close phylogenetic relationship and cytogenetic similarities to S. bicolor and its resistance to important sorghum pests and pathogens such as sorghum midge and sorghum downy mildew. A vegatatively vigorous interspecific hybrid was obtained from a cross between a cytoplasmic male-sterile S. bicolor plant and S. macrospermum by using embryo rescue and in vitro culture techniques. The hybrid was morphologically intermediate to S. bicolor and S. microspermum in leaf width, leaf pubescence, plant height, inflorescence morphology, chromosome number, and nuclear DNA content. It was male-sterile like its ATx623 female parent. The hybrid produced no offspring when used as the female parent in a backcross with S. bicolor. This is the first confirmed hybrid between S. bicolor and S. macrospermum, and to our knowledge it is the first reported hybrid between S. bicolor and any Sorghum species outside the Eu-sorghum section.