Germinative energy of Eucalyptus regnans seed.  A. Ashton, B. Roberts and N. Kelly.  December 2002.  23pp. (unpubl.)

SUMMARY

I. Effect of incubator conditions

Standard germination testing of eucalypt seed lots has indicated some noticeable differences in germinative energy, in addition to variations in viability. The objective of this study was to investigate whether Eucalyptus regnans seed lots can be categorised according to their speed and completeness of germination, independently of variation within the seed testing environment (incubator). Seed lots with different apparent germinative energy (vigour) were germination tested to observe the effect of variation within the incubators on the germinative energy of the seed.

This experiment found that the main factor contributing to observed germinative energy differences between seed lots was the quality of the seed. However, shelf position within an incubator and distance from the light source did significantly affect the germinative energy of a seed lot. Knowing this, current seed testing practices must now be modified to minimise the effect of shelf position on germinative energy. To do this it will be necessary to place the four replicates of any given seed lot on different shelves, and as far as practical from the incubator lights.

In view of earlier research, it is also recommended that research be conducted to establish whether a test regime of alternating light and dark conditions would be better than continuous light for determining the germination potential of E. regnans.

Now it is clear that differences in germinative energy between seed lots, whilst variable, are not entirely caused by the laboratory testing environment, the next step is to establish what effect these differences in inherent germinative energy have on the performance of the seed lot in the field (see Parts II and III).

II. Mid-elevation field study

Currently seed lot viability is used to calculate broadcast sowing rates. Seed quality measures other than seed lot viability may prove to be useful in adjusting the time or rate of sowing of eucalypts to ensure regeneration success. Germinative energy (the speed and completeness of germination) is one such measure of seed quality. Whilst this is calculated in the laboratory testing procedure, it is important to understand how seed lots of different germinative energy perform in a field environment.

This initial study examined the germination results over one year of two seed lots with high and low germinative energy sown on a field site at 760 m elevation.

Although the results were not statistically significant, there was indication that seed lots that show a higher germinative energy in the laboratory produce more germinants than lower energy seed lots, and that these germinants may also have higher rates of survival and growth. This highlights the need to treat lower germinative energy seed lots with caution when recommending sowing rates.

III. High and low elevation field study

This experiment was conducted to determine if the germinative energy of E.regnans seed in the laboratory correlated to field performance at the margins of its elevational distribution. A total of 5 seed lots of varying germinative energy levels were sown at each of two sites (350 m and 1040 m elevation) in March and May 1999.

In contrast to the previous experiment (Ashton & Roberts, 2002) no correlation was found at either elevation that was used in this study.

Differences in germination patterns were found between the high and low elevation sites, and these are in accordance with previously published work on the subject by Lutze et al (1998) and Dignan (2002). These are summarised below

• The timing of germination from all the seed lots was not related to measured seed quality, and was independent of sowing time at the higher elevation.
• Seed sown at high elevation had a 0% survival rate if germinated before mid August, regardless of time of sowing. Later sown seed fared better, as not all the seed had germinated before the heavy frosts.
• Rate of survival was much higher at low elevation.

Problems were experienced with obtaining a consistent laboratory result for germinative energy. Until such time as this variation can be ruled out it will be difficult to predict the field performance of eucalypt seed lots based on laboratory performance.