Articles
TREATMENT AND GERMINATION OF TETTRAPLOID FREESIA SEED: HOT POTENTIALITIES AND COLD FACTS
Germination may be additionally improved by either osmotic priming using PEG ‘6000’ or thermodormancy treatment at 25°C since these treatments allow the embryo to enlarge and differentiate before sowing.
However the advancement resulting from these two treatments is largely lost on air drying, but this is not so with acid scarification.
Freesias grown under glass for cut flower production may be raised from either seed or corms.
Production of high quality flowers during the autumn and early winter months, ie September – December, requires that the plants are raised from seed.
These seeds are usually direct drilled into the glasshouse during the months of March, April and May and emergence occurs over a period between three and six weeks after sowing.
In order to reduce heating costs growers may chit the seed in moist peat or sand, then broadcast the mixture of the medium and germinated seed in the glasshouse.
This successfully shortens the time to crop establishment in the glasshouse, but the resulting crop is unevenly spaced and losses occur due to radicle damage inflicted during broadcasting.
Consequently there is a need for a treatment which will hasten seed germination but which will leave the seed in a form that can be safely drilled into the glasshouse.
In the laboratory working with tetraploid seed, Parigo’s Supreme Mixed, germination, ie radicle emergence, occurs most rapidly at temperatures between 15°C and 20°C. At 10°C germination occurs very slowly whilst at 25°C it is almost completely inhibited.
It is also interesting to note the interaction between light and temperature such that light inhibits germination at 20°C but has very little effect at 15°C (Figure 1). The presence of light however is hardly likely to be a problem in the glasshouse where seed is sown approximately ½ inch deep at a temperature maintained around 15°C, but, as will be seen, it is of great importance in the work about to be reported (Humphries, 1976).
The technique of seed priming (Heydecker, Higgins and Gulliver, 1974) has been shown to increase the rate and uniformity of germination of many species of vegetables and ornamentals and appeared to have application to Freesia seeds (Heydecker and Morris, 1976). Following their work and using their optimum temperature for treatment, ie 20°C, seeds were primed in contact with polyethylene glycol (PEG)