FACTORS AFFECTING THE GERMINATION AND ESTABLISHMENT OF MONOGERM SUGAR BEET
3.3.1 Germination tests at standard temperatures and 7.5°C with untreated seed
The results of the standard germination test (Expt 1), show that considerable variation exists between Monogerm sugar beet seed lots, in germination performance, even though the test conditions were intended to be ideal for germination. There must therefore be inherent seed factors influencing the observed performances, which make beet germination tests of relatively low precision, as earlier found by Hibbert & Woodwark (1969).
This was confirmed at the end of the experimental period when Expt 1 was repeated. Lot 5 reached a final germination 18% higher in the re-test while the other seed lots did not differ by more than 7.5%.
Inherent variation in seed lots limits the value of comparisons between tests and treatments, but generalised conclusions can be made.
Two of the three lots which exceeded 90% germination in Expt 1 had been commercially processed, and also had fast M.G.T. values but as both processed and unprocessed samples of the same seed lot were not available for comparison, it cannot be confirmed that processing improves seed performance.
The results of Expt 2 clearly indicate that in all seed lots germination proceeds at a slower rate at 7.5°C than at standard temperatures. The extended period of germination and the lower final germinations recorded indicate a variation in individual seeds within seed lots in germination performance at 7.5°C.
This test is therefore measuring an aspect of seed vigour in the seed lots i.e. the ability to germinate at less than optimal temperatures. The M.G.T. values and the number of seeds which subsequently germinated when the petri-dishes were incubated at standard temperatures could be used to quantify this.
The amount of temperature inhibition of germination observed in the seed lots was considerably less than the values observed by Brown (1980) working at lower temperatures (5-7°C) with several seed lots. Scott et al (1973) showed that Sharpes Klein E was markedly inhibited at 5°C and severely so at 3.5°C in germination tests and also emerged poorly when sown early into a cold soil. This shows that beet seed germination is very sensitive to temperature over the range 3.5 - 7.5°C. Further work in this area would be of value for breeding, i.e. selecting for low temperature germination and also for testing the low temperature performance of existing varieties.
The dissection of the remaining ungerminated seeds from Expt 2 showed that as the rubbed Lots 2 5 contained more empty and shrivelled true seeds their maximum potential germination would have been lower than the other lots. It was assumed that these seeds were incapable of germination as they had been in the petri-dishes for over fifty days. This assumption may not hold for all seeds as Scott et al (1972) showed that underdeveloped seeds steeped in water or GA3 solution emerged better than untreated seeds.
When the seed lots are compared on a maximum potential germination basis i.e. comparing the number of other ungerminated seeds, Lot 2 is similar to Lots 1, 3 & 4. If processing could successfully remove the empty and shrivelled seeds, Lot 2 would have performed better in Expt 1. Lot 5 however, contained a high number of seeds which failed to germinate for other reasons as well as seeds which were empty or shrivelled. Therefore Lot 5 would not have performed well in Expt 1 even if the empty and shrivelled seeds had been removed by processing.
The poor performance of Lot 5, i.e. low final germination and slow M.G.T. at both standard temperatures and 7.5°C may have been due to the inhibitor content of the seed coat, but the extract from Lot 5 was actually slightly less inhibitory than the extract from Lot 2 on cress M.G.T. However, the exact chemical nature of the extracts was not determined and cress and beet seed may respond differently to different inhibitors.
The effects of inhibitors could have been removed from the tests by careful (dry) excision of true seeds or alternatively removal of the seed coat by a dentist's drill as used by Battle & Whittington (1969b). This method improved final germination and speed of germination of a seed lot but in addition to removing the effects of inhibitors, less energy would be required for germination and more oxygen would be accessible to the true seed. The effects of inhibitors would therefore be over-estimated by this method, but it reveals that physical factors of the seed coat can also influence germination.
The number of tight seed caps on seeds could be one such physical factor involved in the performance of Lot 5, as the seed lots differed in the amount of seed caps lost in the advancing procedure. The rubbed lots lost few compared with the processed.
The effects of chipping the seed cap before testing are discussed in Section 2.3.5.
Another possible explanation is that seed deterioration had occurred, but the viability of beet seed is retained over long periods of storage (Section 2.3.2) and the re-tested germination of Lot 5 under standard conditions implies that the performance has improved with time. This is unlikely in 5 year old seeds and no similar observation was recorded with Lot 2 which was also 5 years old.
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]
