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Proceedings
VIGOUR IN GRASS SEED
Anders Lomholt
Danish Institute of Agricultural Sciences, Department of Plant Biology
Research Center Flakkebjerg, DK-4200 Slagelse, Denmark
e-mail: anders.lomholt@agrsci.dk
It is generally accepted that maximum seed quality is reached at physiological maturity which is defined as maximum dry weight. Although many factors potentially influence the physiological age of seeds, the two most important factors include temperature and moisture content of the seed. Differences in physiological age influence storability and the ability to germinate under stress conditions - vigour.
One approach to assessing seed vigour is based on the normal pattern of changes in seed germination with time - a survival curve. By artificially accelerating the ageing process, a similar curve can be obtained. This observation forms the basis for two different assessment methods, Accelerated Ageing (AA) (Delouche & Baskin, 1973) and Controlled Deterioration (CD) (Matthews, 1980). Both the AA and CD methods expose seeds to elevated temperatures and water content for a pre-determined period. The most noticeable difference between the two methodologies is a more precise control of water content in the CD test. One year old commercially produced ryegrass seeds were used for the experiment.
The Accelerated Ageing test was carried out in air-proof plastic box. The seeds were heid on a piece of fibre material placed on a fine metal mesh above the surface of 50 ml distilled water. Seeds were held in a cabinet at 41-55° celsius over 12-144 hours.
For the Controlled deterioration test, a weighed sample of seeds of known moisture content was placed on a germination paper moistened with 3,0 ml of distilled water in a petri dish and allowed to imbibe to the desired moisture content. The seeds were sealed in a foil packet and left at 5° C for 15-20 h to ensure a homogeneous distribution of water through out the samples. Samples were then held in a water bath at 45° C for 0, 24, 48 and 72 hours. After both deterioration treatments the seeds were set to germinate as described by the International Seed Testing Committee (ISTA). Results obtained from CD-testing for 0, 24, 48 and 72 hours, indicates that this span encompasses the entire spectrum of physiological age in ryegrass. A deterioration treatment of 24 hours showed a small decrease in germination while very few seeds germinated after 48 hours. Using a treatment period in-between the two seems appropriate. After using the AA technique on ryegrass, a smooth fitting curve could be generated between increasing hours of ageing and decreasing rates of germination. By raising temperatures by only a few degrees, large increases in the ageing process were observed. The preliminary results indicate that an ageing temperature of 51° C for 48 hours is appropriate for ryegrass.
In order to gain greater insight of the deterioration process during vigour testing, abnormal germination was observed. The results obtained show a negative correlation between increasing physiological age and amount of abnormal germination.
Keywords: vigour; ryegrass; ageing; germination.