Manifold effects of the cyanogenic loci in white clover

Abstract

SUMMARYIn white clover alternate alleles Ac/ac and Li/Il at two unlinked loci determine the presence/absence of cyanogenic glucosides and the enzyme linamarase respectively. Plants possessing both cyanogenic glucosides and enzyme are cyanogenic. Morphological measurements were made on a random sample of plants from a population polymorphic at both loci. Individuals possessing linamarase had larger leaves than those lacking the enzyme. Competition experiments between all phenotypes showed a significant effect of Li phenotype frequency on total yield. Competitive interactions were such as to maintain polymorphism at the Li locus. It is concluded that the pattern of variation at the Ac and Li loci cannot be adequately explained by selection which discriminates between cyanogenic and acyanogenic phenotypes.

Biologically active secondary metabolites in white clover (Trifolium repens L.) – a review focusing on contents in the plant, plant–pest interactions and transformation

“…In earlier times white clover had low cyanogenic levels, as all varieties in eastern European countries were bred from local populations, which were low in cyanogenic compounds. Since that time, breeders have been developing better, pest resistant varieties with higher growth rates, and often use breeding lines containing genes responsible for high levels of cyanogens (Ennos 1981a;Stochmal and Oleszek, 1997). As previously mentioned, Swiss varieties that release more than 370 mg/g of HCN are not recommended (Lehmann et al, 1990), and Coop and Blakley (1950) considered HCN of 700 mg/g dry weight as a safe limit for new clover strains.…”

The effects of altitude, aspect, grazing and time on the proportion of cyanogenics in neighbouring populations of Trifolium repens L. (white clover)

“…Consequently, dry sites carried fewer cyanogenic individuals, although no such differential selection was observed between Li-and lili genotypes. However, Ennos (1981a) observed frequency dependent competitive interactions between Li-and lili genotypes, and suggested that these might maintain the polymorphism for the Li locus. He noted that Li-individuals tended to produce larger leaves than lili genotypes in one wild population, and Ennos (1981b) showed better wild survival of Li-seedling transplants than of lili transplants.…”

A polymorphism for a lethal phenotype governed by two duplicate genes in Mimulus guttatus

“…In the former case there are two unlinked loci, one determining whether the snail is banded, the other deter- Cyanogenesis is determined again by two unlinked loci, one determining the presence of a cyanogenic glucoside, the other an enzyme that breaks down the glucoside to produce cyanide. In neither case is it clear what maintains the polymorphism (Jones et al, 1977;Ennos, 1981), but in neither case is one of the genotypes lethal as in the example described here. Numerous cases of lethal polymorphisms are known in cultivated and wild plants (Crumpacker, 1967), and some albino phenotypes are known to be governed by the epistatic interaction of two or more genes (Crumpacker, 1967;Demerec, 1923 (Crumpacker, 1967;Apirion & Zohary, 1961).…”