Towards early-stage chilling tolerance for European energy sorghum

Interest is growing rapidly in the use of sorghum as a potentially insect-resistant and drought-tolerant alternative to maize for energy production in central Europe. An absolute prerequisite for sorghum biomass production in the short growing season of Germany is early-stage chilling tolerance. We are employing classical and next-generation genome mapping techniques to identify and characterize novel genetic variation for chilling tolerance and introgress the responsible genes into breeding lines with desirable bioenergy characteristics. Deep phenotyping and multi-trait QTL analysis was performed in a highly diverse RIL population from a sweet x grain sorghum cross that segregates strongly for morphological, agronomical, bioenergy-related and abiotic stress tolerance traits. Genome regions of most interest for early chilling tolerance were dissected by low-depth resequencing of 60 RILs showing extreme phenotypes for seedling survival under chilling stress. The mapping parents were resequenced at 6x depth by 100bp paired-end Illumina sequencing. We selected 3000 high-quality genome-wide and QTL-derived SNPs by in silico-validation in a total of 6 whole-genome Sorghum bicolor sequences, including 3 grain and 3 sweet sorghum genotypes. An Infinium array containing these SNPs is currently being generated for joint linkage and association mapping in a panel of 200 genetically diverse genotypes and three biparental populations showing broad phenotypic diversity for chilling tolerance and other traits of interest. In this way we expect to identify germplasm, genes and SNP markers that can be used for genomics-based breeding to improve abiotic stress tolerance and biomass yields for bioenergy production.