Elimination of a Reproductive Barrier Facilitates Intergeneric Hybridization of Sorghum Bicolor and Saccharum.

Sorghum (Sorghum bicolor) and sugarcane (Saccharum spp.) are now being bred to enhance the quantity and quality of biomass while maintaining or improving biotic and abiotic stress tolerances.  Introgression of complementary traits between sorghum and sugarcane may be an important tool for breeders, as they work toward these objectives.  We show that by using a sorghum line with the iap (inhibition of alien pollen) trait, inter-generic Sorghum bicolor x Saccharum spp. hybrids can be readily produced.  Using Tx3361 as sorghum seed parent, 14,161 seed were produced from 252 sorghum x Saccharum spp. crosses using 67 basic and commercial breeding clones as pollen parents.  Avoiding vivipary through premature seed harvest and eliminating a physical barrier by removing the seed coat increased seedling recovery rates from 1.5% to 33%.  Using these methods, our programs have grown 1,371 sorghum/saccharum intergeneric hybrid plants. These hybrids displayed a wide range of phenotypes that included traits from both Saccharum and Sorghum.  Seed set, with a high of 53%, was affected by the sugarcane pollinator with the best pollinators having an above average pollen rating and favorable genetic and/or genomic compatibility.  Continued breeding and selection of sugarcane pollen parents that increases seed set and improves seed quality will further enhance successful hybridization.  The ability to transfer drought tolerance from sorghum to sugarcane or to introgress enhanced sugar production from sugarcane into sorghum could significantly influence energy and sugar production throughout the world.  Further, a Sorghum/Saccharum hybrid with high sugar-accumulating capacity and enhanced water-use efficiency that is propagated by seed would have added value.  Additional research on sorghum seed parents and sugarcane pollinators must be completed to make seed propagation a viable option.