FACTORS AFFECTING THE GERMINATION AND ESTABLISHMENT OF MONOGERM SUGAR BEET
2.2.8 Alternative seed treatments
Sugar beet seed has to be processed between harvesting and sowing to eliminate inferior seed, and give good seed a better chance of good and fast emergence. The standard procedure listed removes empty and shrivelled seeds and multigerms, and gives protection against some pests. and pathogens but often field performance is far from perfect, therefore better treatments should be sought. The problem in finding suitable alternatives is not that treatments do not improve seed performance when used singly but more often because there are practical difficulties or incompatibility with existing treatments or simply the cost and time involved (Tonkin 1979).
(i) Washing
Longden (1973) showed how 21 rinses in 3.5 hours gave the best response in glasshouse and field trials with natural and partially processed seed; but when agitated, washed seeds showed a greater tendency to lose seed caps and therefore this was an unsuitable treatment. Washing had similar effects on the performance of both mature and immature seed.
(ii) Advancing
The object of advancing is to allow seeds to imbibe water and develop physiologically up to the point of radicle elongation and then be dried back, holding the seeds at this point before sowing. This reduces the period between sowing and emergence in the field.
The optimum advancing technique for sugar beet was determined by Longden (1971), (equal weights of seed and water in airtight containers for 24h, repeated 3 more times with a 48h air drying interval after each soaking). Advancing increases the number of cells in the true seed but the treatment does not increase the size of individual cells so that the germination process does not therefore result in large changes in embryo volume before the radicle elongates, but like washing, advancing increases the tendency for premature loss of the seed cap. An extremely gentle drill mechanism would therefore be required. Fluid drills may be developed for practical use.
While washing was calculated to be equivalent to a very much higher than normal rainfall over the seed plant, rainfall effects are more similar to advancing than washing, i.e. a small amount of water in contact with the seed for a longer time.
(iii) Osmotic priming
This treatment is also designed to get the seed in a better physiological state for quick emergence. Trials with various concentrations and priming periods in polyethylene glycol or salt (KNO3 + K3 P04 H20), (Longden, Johnson, Darby & Salter 1979) gave poor and inconsistent results and no reduction in the time spread of germination. Priming is therefore too unreliable to use in practice.
(iv) Water steeping
Longden et al (1979) also looked at the effects of a 24h soak in 10 x the seed volume of water @ 1°C followed by re-drying. Steeping gave uniform germination but poor field performance. Scott, Wood & Harper (1972) however found that a 24h soak in water @ 20°C hastened emergence and improved final germination. The steeping process probably has effects on physiological developments and also removes germination inhibitors.
(v) Plant growth regulators
Scott et al (1972) compared steeping seed in solutions of kinetin (K), 6-benzyl-aminopurine (BA) and gibberellic acid (GA3) with water only. All solutions gave better field emergence than water but also showed a response to concentration. The optimum concentrations were BA 1 - 10 ppm, K 50 - 100 ppm, GA3 - 100 ppm which nearly doubled the seedling weights.
(vi) Size grading of seed
Longden, Scott & Wood (1974) devised a size grading method which could produce a seed lot containing 90% monogerms and a germination of 80%, providing the unprocessed raw seed had at least 50% germination. The method included grading by thickness to remove multigerms, and grading by diameter and aspiration to remove small and non-viable seeds. The variation in size range was also reduced in the process. However, an ideal sequence for size grading cannot be formulated as there is much variation between original seed lots due to effects of season, seed production agronomy and variety. The optimal adjustment and sequence for one seed lot may be totally unsuitable for another.
(viii) Treatment combinations
Any number of treatments can be used on a seed lot but to be of value they should be
a) fully compatible,
b) additive in effect or, preferably,
c) synergistic (Longden 1976).
Longden (1976) tried washing, E.M.P. steeping, Thiram soaking and advancing in sequence on a seed sample of Amono graded 3.18 - 3.57 mm. One or more of the treatments were omitted on other Amono samples so that a total of 16 different combinations of treatments were obtained for comparison. When analysed, different aspects of seed performance were affected and complex interactions occurred - some combinations gave faster emergence, others larger shoots. In general, as more treatments were applied detrimental effects were observed, e.g. E.M.P. had positive effects on seed performance when used singly, but negative in combination, (when additional soaking let Hg penetrate the embryo). It was probable that there was considerable overlap in the effects of single treatments and there was no evidence of cumulative or synergistic benefits from combinations. Therefore only one treatment involving water or a solution should be used on a seed lot and in practice this is the E.M.P. steep to control seed borne fungi.
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]
[2.1] [2.2.1] [2.2.2] [2.2.3] [2.2.4] [2.2.5] [2.2.6] [2.2.7] [2.2.8]
