Latent Variability in Ryegrass
Wimmera ryegrass is a highly purified strain of Lolium rigidum, a 7-chromosome species native to the Mediterranean region. It is a spring annual that attains flowering without cold treatment. One would therefore not expect vernalization to have any effect on such a species.
J. P. Cooper (1954) found that when Wimmera ryegrass is sown outdoors in spring it will initiate flowering at the seventh to eighth node (mean 7.2). When it is sown in a heated greenhouse and given continuous light, considerable previously hidden variability is disclosed, and the seedlings initiate flowering at various nodes, ranging from the fourth to the twenty-first, as shown in Table V (mean node, 12.5). The variability will again be hidden if, before the continuous light treatment, the seeds are vernalized for six weeks at 3°C. When the cold treatment is followed by continuous light, the plants will initiate flowering at the fourth to the sixth node (mean 5.1).
Wimmera Ryegrass, Lolium rigidum, Latent Variability Revealed at Continuous Illumination (After Cooper, 1954)
|Node of floral initiation||4-5||6-7||8-9||10-11||12-13||14-15||16-17||18-19||20-21||Total|
|Vernalization at 3°C||11||9||20|
|Heated greenhouse only||2||4||7||7||5||1||2||2||30|
The cold treatment apparently starts and equalizes certain gene-controlled processes related to development. No previous selection has taken place for the combination of heated greenhouse and continuous light, and the plants accordingly reveal a considerable degree of residual variability under this artificial condition.