Wide Hybridization and Utilization of Wild Relatives of Sorghum

Abstract

The process of wide hybridization refers to hybrids created through interspecific or intergeneric crosses of related species to extract useful and novel traits that protect or enhance the yield or quality of the domesticated crop. Sorghum contains approximately 25 recognized species that show significant variation in plant morphology, genetic and genomic diversity with an eightfold range in DNA content, and geographic distribution. Traits that increase the value of sorghum production have been reported in many of these species including resistance to sorghum midge, shootfly, and spotted stem borer. However, introgression of any traits has only been possible with species in the section Eusorghum due to preand post-fertilization barriers that isolate the other species. Now the creation of wide hybrids has been expanded beyond section Eusorghum. The Inhibition of Alien Pollen (Iap) gene that makes it possible to overcome pre-fertilization barriers by reducing adverse pollen–pistil interactions has been used to produce additional interspecific hybrids with species from sections Chaetosorghum, Parasorghum, and Stiposorghum. Post-fertilization barriers can be eliminated through embryo rescue techniques and the use of 2n gametes. Using 2n gametes as a vehicle to transfer genes by creating bridges that overcome ploidy and genomic differences between species is now being explored. With the chemical hybridizing agent trifluoromethanesulfonamide (TFMSA) the number of parental combinations and the number of florets that are emasculated are no longer limiting factors when developing strategies for creating wide hybrids. Accessing via wide hybridization novel traits that were previously unavailable is now possible.