Sorghum TILLING Population- A Community Resource for Sorghum Improvement.

Sorghum (Sorghum bicolor L. Moench) is ranked as the fifth most important grain crop and serves as a major food staple and fodder resource for much of the world, especially in arid and semi-arid regions.  The recent surge in sorghum research is driven by its tolerance to drought / heat stresses and its strong potential as a bioenergy feedstock.  Completion of the sorghum genome sequence has opened new avenues for sorghum functional genomics.  However, the availability of genetic resources, specifically mutant lines, is limited.  Chemical mutagenesis of sorghum germplasm, followed by screening for mutants altered in important agronomic traits, represents a rapid and effective means of addressing this limitation.  A sorghum mutant population consisting of 1,600 lines was generated from the inbred line BTx623 by treatment with the chemical agent ethyl methanesulfonate (EMS).  Numerous phenotypes with altered morphological and agronomic traits were observed from M₂ and M₃ lines in the field.  A subset of 768 mutant lines was analyzed by TILLING using four target genes.  A total of five mutations were identified resulting in a calculated mutation density of 1/526 kb.  Two of the mutations identified by TILLING were verified by sequencing in the gene encoding caffeic acid O-methyltransferase (COMT) in two independent mutant lines.  The two mutant COMT lines segregate for the expected brown midrib (bmr) phenotype, a trait associated with reduced lignin content and increased digestibility.  The diversity of the mutant phenotypes observed in the field, and the density of induced mutations calculated from TILLING, indicate that this mutant population represents a useful resource for sorghum genomic studies.