Inheritance of Dhurrin Content in Mature Sorghum Leaves

Seedlings of both KS8 and N32 sorghum [Sorghum bicolor (L.) Moench] were high in dhurrin [p-hydroxy-(S)-mandelonitrile-BD-glucoside] and thus in hydrocyanic acid potential (HCN-p), but the HCN-p of mature leaves from field-grown plants of KS8 was only about one-tenth as high as that of N32. A study of the inheritance of this large difference between KS8 and N32 revealed that a single major gene pair was responsible. There were no obvious maternal effects and Fl’S were generally intermediate in HCN-p level between the two parents, indicating that neither high nor low HCN-p was completely dominant. HCN-p level was inttuenced by genetic background since mean values of the low and intermediate HCN-p classes increased slightly as the proportion of genetic background ascribable to N32 was increased. A survey of 102 additional sorghums revealed that the gene for low HCN-p carried by KS8 does not appear to occur widely because KS8 had the lowest HCN-p of all entries assayed. Additional index words: Cyanogenesis, Genetics, Hydrocyanic acid, p-Hydroxybenzaldehyde, Prussic acid, Sorghum bicolor (L.) Moench, Spectrophotometric assay. T HW biosynthesis of the cyanogenic glucoside, dhurrin [p-hydroxy-(S)-mandelonitrile-~5-D-glucoside], in sorghum [Sorghum bicolor (L.) Moench] has been studied extensively, and much has been learned about the process (1). However, studies of the inheritance of dhurrin content in this species have been much less conclusive. Nass (10) reviewed published reports on the inheritance of cyanogenesis in sorghum, various Lotus species, and Trifolium repens L., and concluded that the situation in sorghum was more complex than that in other species. There was general agreement that the hydrocyanic acid potential (HCN-p) of sorghum leaves was a heritable trait, but the reports failed to agree on such matters as dominance of low or high HCN-p and the number of genes involved. Lack of agreement ma.y have been due in part to differences among the various studies with respect to lines and cultivars used, conditions of growth and sampling, and analytical procedures. Krauss (7) concluded that HCN-p in sorghum was governed by four gene pairs with additive effects and without dominance. His work was based on crosses among four sorghum cultivars differing in HCN-p. More recent reports have included information about the HCN-p of hybrids and their parents in forage sorghum (13, 15) and also in sudangrass and sudangrass-sorghum combinations (14), but these studies were not designed specifically to investigate the in-