Mutagenesis, Selection, and Allelic Analysis of Epicuticular Wax Mutants in Sorghum

Epicuticular wax forms an outer coating on the aerial surfaces of many crop plants and is implicated in tolerance to several environmental stresses including drought. Advances in knowledge of biosynthesis and secretion of these leaf surface waxes could lead to improvements in crop-stress tolerance. To study the genetics of epicuticular wax deposition, we screened for bloomless (bm) and sparse-bloom (h) mutants with reduced glaucousness of abaxial sheath surfaces within chemically mutagenized populations of Sorghum bicolor (L.) Moench. We screened over 3974 segregating M-2 head rows with over 160,000 plants and identified 38 putative recessive epicuticular wax mutant alleles. We grouped 31 of these into allelic groups associated with one existing and 18 new epicuticular wax loci. The overall epicuticular wax mutation frequency was 0.88%. In addition, analysis of the mutant segregation frequencies within the M-2 rows allowed us to calculate the existence of five target meristem cells in a dormant (M-0) seed embryo. The high epicuticular wax mutation rate and identification of 19 epicuticular wax loci indicate the presence of a complex genetic system of epicuticular wax production in sorghum as has been shown in other species. The new bloomless and sparse-bloom mutants identified here have a wide range of phenotypes and constitute a valuable resource for studies of the genetics and biosynthesis of epicuticular waxes and their effects on tolerance to environmental stresses such as drought.