A genetic dwarf (dd) of Lolium perenne is described. Its effect is to reduce cell elongation in the leaf blade and sheath. As a result, successive leaves on the shoot, instead of increasing in length, as in the normal plant, remain short and broad, and a small dwarf rosette is formed. The rate of leaf appearance on the main shoot is unaffected.
Gibberellic acid, at a weekly dose of 1 cc. of a 50 mgm./1 solution per plant, results in increased cell elongation in the leaf blade and sheath, and brings the genetic dwarf within the normal phenotype for both leaf and inflorescence development.
Although many genes are known which influence developmental patterns in flowering plants, in few cases is any information available about the possible biochemical mechanisms involved. In certain genetic dwarfs, however, evidence is accumulating that the mutant form can be brought within the normal phenotypic range by treatment with gibberellic acid, a growth-regulating substance derived from the fungus Gibberella fujikuroi (Saw) Wr. This substance increases the length of leaves and internodes in normal plants of many species (Brian et al., 1954), and Brian and Hemming (1955) report that in the pea (Pisum sativum), broad bean (Vicia faba) and French bean (Phaseolus vulgaris) the dwarf varieties show a greater response than the tall varieties, the different genotypes producing similar phenotypes after treatment. In maize, Phinney (1956) tested six non-allelic dwarf mutants and found that four of them could be converted into phenotypic ally normal plants by treatment with gibberellic acid.
The present note describes a similar example of this effect on a dwarf mutant of perennial ryegrass (Lolium perenne).