Seasonal Variation in Leaf Hydrocyanic Acid Potential of Low‐ and High‐Dhurrin Sorghums¹

Abstract

The KS8 and N32 sorghum [Sorghum bicolor (L.) Moench] lines are low and high, respectively, in the hydrocyanic acid potential (HCN-p) of mature leaves. This difference is conditioned primarily by a single pair of alleles. The main objective of this study was to determine, at various stages of plant growth and various times during the growing season, the HCN-p of upper leaves and tillers of fieldgrown plants of these two parental lines and of two Iow-HCNop Fl ines derived from crosses between KS8 and N32. The four entries were grown in a randomized complete block design with three replications in 1985. Samples of leaf tissue were dried, ground, and extracted, and cyanide in the extracts was assayed colorimetricaily. Using a mean HCN-p level of 500 mg kg-~ dry wt to separate safe from unsafe sorghum forage, all samples of KS8 mature leaves and tillers would be considered safe, and all N32 samples would be considered potentially dangerous. Values for most of the samples of the F.~ lines fell within the safe range, but some samples of young regrowth exceeded the 500 mg kg-~ limit. Regressions of HCN-p on height for upper leaves of main stems and of tillers indicated a significant negative relationship for all entries except for leaves from the main stems of KS8. However, the relationship was not close enough to support the use of plant or tiller height as a reliable indicator of HCN-p. Levels of HCN-p also were determined for mature leaves and young regrowth of hybrids involving KS8, N32, and 'Redlan' sorghums as seed parents and NP25, 'Piper,' and 'Greenleaf' sudangrasses [S. sudanense (Piper) Stapf] as pollinators. Results indicated that for minimizing the risk of cyanide poisoning, KS8 would be the seed parent of choice, and NP25 and Piper would be the preferred pollinators.

Factors affecting the hydrogen cyanide potential of forage sorghum.

“…= 149) in 1987188 and 66, 141 and 234 (l.s.d.= 56) in 1988189 (present authors, unpublished). Haskins et al (1987) have shown that, in a Sorghum bicolor line (KS8) selected for very low HCN,, all mature leaves and apical tillers remained below 500 throughout a season in the field regardless of age.…”

“…Many years ago, attention was given to the selection of low HCNp cultivars of sudangrass (Sorghum sudanense) (USDA 1959), but this objective has, until very recently, been largely neglected in the breeding of sorghum X sudangrass hybrids. Some progress has been made (Walcott et al 1986;Haskins et al 1987), but it remains to be shown whether a genotype developed for low HCNp in an environment not conducive to dhurrin formation will maintain a non-toxic level under conditions that are known to raise HCN,.…”

Biosynthesis of the Cyanogenic Glucoside Dhurrin in Seedlings of Sorghum bicolor (L.) Moench and Partial Purification of the Enzyme System Involved

“…In white clover (Trifolium repens L.), the Ac/ac locus controls the production of the cyanogenic glucosides ' linamarin and lotaustralin and plants homozygous for the ac allele are acyanogenic (5). Traditional breeding has produced 'low cyanide' cultivars of cassava ( 11) and sorghum (12), but so far it has not been possible to obtain totally acyanogenic varieties. The polymorphism of cyanogenesis in white clover (5,14) demonstrates that the cyanogenic character is not of vital importance for normal growth and development of each individual cyanogenic plant.…”

Early Seedling Growth Characteristics Relate to the Staygreen Trait and Dhurrin Levels in Sorghum

“…Dhurrin is derived from the amino acid tyrosine and comprises up to 30% of the DSW of the leaves and coleoptiles of etiolated sorghum seedlings (Saunders and Conn, 1977;Halkier and Møller 1989). The cyanide potential of sorghum seedlings is highest at germination, peaks at 4 DAE (Haskins et al, 1987), and remains unchanged for seedlings up to 8 d of age, irrespective of nitrogen fertilization (Busk and Møller, 2002). The dhurrin content in seedlings can be determined by the cyanide potential; a quantitative measure of dhurrin content based on cyanogenesis (the catabolism of dhurrin by the enzyme dhurrinase).…”

“…Seasonal variability in postflowering drought occurrences makes selection for the staygreen trait unpredictable and the efficiency and reliability of screening for the trait using only conventional breeding low. In sorghum, dhurrin content in the tip of young seedlings reaches 6% of the dry weight (Akazawa et al, 1960;Halkier and Møller, 1989), and this content in both seedlings and older plants depends highly on growth conditions and genetic background (Haskins et al, 1987). Here we report a screening method using early seedling growth characteristics of sorghum lines of known dhurrin level grown in sand with no inorganic nutrients supply.…”