FACTORS AFFECTING THE GERMINATION AND ESTABLISHMENT OF MONOGERM SUGAR BEET
3.3.3 Germination tests with treated seed
None of the treatments used in this investigation noticeably improved final germination at standard temperatures in any of the seed lots with the possible exception of Lot 5 when compared with Expt 1. If however, the re-tested final germination for Lot 5 is used there would appear to be no improvement in final germination of Lot 5 by treatments. No determination has satisfactorily explained the performance of Lot 5, therefore it may differ from the other lots in some unknown way in response to treatments but being poorer than the other lots, a greater capacity for improvement by any treatment might be expected.
It can however be concluded, at least for the other seed lots, that at standard temperatures in petri-dishes with adequate water, GA3 solution, Advancing with water and Advancing with GA3 solution cannot encourage seeds to germinate which could not do so without treatment.
The treatments did however shorten mean germination times by different amounts. The following is an attempt to explain the observations.
1. The GA3 solution in the dishes must have accelerated the physiological development of the germination process in at least some of the seeds so that radicle emergence was observed earlier than in Expt 1.
2. The mean germination times for seed advanced in water, which were even faster than the GA3 solution in the petri-dishes, would be due to early stages in the physiological development of the germination process occurring during the advancing procedure. Physiological development can be quantified by assessing cell division and Longden (1971) showed that this occurs in the advancing procedure. Cell division must also occur in untreated seed in the petri-dish before radicle emergence but as cell division and other physiological processes take time and can only occur in imbibed seed, seeds which are partially developed (i.e. advanced) before being placed in the petri-dishes should take less time than untreated seeds, to reach radicle emergence, i.e. observable germination.
3. The combination treatment Advancing with GA3 solution resulted in faster M.G.T. values than the water advancing treatment due to the accelerating effects of GA3 on the physiological development of germination both during the advancing procedure and in the petri-dishes thereafter, or in at least one of these phases.
The effects of GA3 and Advancing on the rubbed seed lots can now be compared, as shown in Table 7.
Although GA3 solution in the petri-dishes is not strictly compatible with water Advancing for addition, to compare with GA3 Advancing, the combination treatment shows a greater reduction in the M.G.T. values of the 3 lots than either of the individual treatment reductions, or the sum of the 2.
This incompatibility, lack of precision and because the experiments were carried out at different times precludes determination of whether the effects are additive or synergistic (Longden 1976)
The anomalous result of GA3 apparently slowing down the germination of Lot 5 may have arisen by chance but possibly Lot 5 responds differently to treatments such as GA3, as suggested earlier in this section.
Clearly this set of experiments was inadequate to explain the nature of the effects of GA3 and Advancing. A larger experiment which included the following additional treatments would be required to elucidate the situation.
1. Water advancing plus GA3 in the petri-dishes.
2. GA3 Advancing plus GA3 in the petri-dishes.
3. GA3 Advancing followed by thorough washing before testing.
4. Thorough washing of untreated seed before testing.
The processed seed lots (Lots 3 & 4) which were advanced in water after removal of the pelleting material however showed the shortcomings of multi-treatments involving solutions, where loss of the seed cap occurred with many of the seeds (Longden 1976). If advancing were to be used in practice it would be carried out before the pelleting procedure or in combination with fluid drilling and loss of seed caps may not be such a serious problem (Longden et al 1979).
In this investigation however, the definition used for germination was unsuitable for advanced processed seed. The seeds which had lost seed caps in the advancing procedure were excluded from the germination tests and this was a high proportion of the processed seed lots. Presumably it was the faster germinating seeds which were removed and therefore the reduction in M.G.T. values of the processed seed lots were under estimated in this investigation by the bias of selecting slower germinating seed. That Lots 3 & 4 should lose more seed caps than the rubbed lots is in agreement with the faster M.G.T. values obtained for the processed lots in Expt 1.
An improved germination definition for advanced seed in tests could be to consider only seeds with radicles > 5 mm as germinated and others with or without caps as ungerminated. Fewer seeds would be excluded after advancing. However, this definition would have to be used in all other experiments for fair comparison. Mean germination times would be longer than if the original definition was used in any one test situation.
A further area in which experimentation could be continued would be in determining if the advancing technique in terms of seed: solution ratios, number of cycles and temperature were optimal. The effect of advancing on inhibitors could also have been investigated by taking extracts of advanced seed and assaying this on cress germination.
The test with water advanced seed, in petri-dishes at 7.5°C (Expt 3ii) showed that advancing almost completely removed the low temperature inhibition of germination observed in Expt 2. This implies that there is a critical stage which is inhibited in some seeds but once passed, then germination can proceed at 7.5°C. Some kind of priming must be occurring in the advancing procedure. The M.G.T. values in this test were faster than in Expt 2 (untreated seed at 7.5°C) as physiological development had occurred before the test commenced as described earlier for advancing and testing at standard temperatures. However, M.G.T. values were not as fast as those obtained with untreated seed at standard temperatures in Expt 1.
Further low temperature tests with GA3, Advancing and GA3 Advancing would have been valuable as Scott et al (1972) predicted GA3 effects were more noticeable at low temperatures and may be of practical value.
FACTORS AFFECTING THE GERMINATION AND ESTABLISHMENT OF MONOGERM SUGAR BEET
[Introduction & Contents] [Chapter One] [Chapter Two] [Chapter Three] [Chapter Four] [Chapter Five] [Chapter Six] [Chapter Seven]
[3.3.1] [3.3.2] [3.3.3] [3.3.4] [3.3.5]
