FACTORS AFFECTING THE GERMINATION AND ESTABLISHMENT OF MONOGERM SUGAR BEET
The factors involved in the establishment of sugar beet have already been described and discussed. The main reasons for poor establishment in the field, other than seed factors are; inadequate seedbed preparation, poor drill performance, pests and diseases, and low spring temperatures.
More efficient utilization of incident radiation could be achieved by improvements in general husbandry or breeding of better varieties, resulting in more regular stands and earlier complete leaf coverage. However this discussion is mainly concerned with methods of improving establishment directly related to the seed used at present. In all cases the final objective is an increase in sugar yields.
The "drilling to a stand" technique as used in the U.K. normally requires at least 70% of all seeds sown to produce healthy plants to prevent yield reductions due to "gappiness" and justify use of the technique (Hull and Jaggard 1971).
A recent survey showed that, in 1980, most fields did achieve emergences greater than 70% although the range was 20-90% (Durrant 1980). Soil texture influenced emergence with loams and clays producing inferior stands compared to organic, silty and sandy soils. Seed excavations in some of the fields in the survey revealed that germination in the field was similar to the laboratory determination and where emergence was low it was due to subsequent death of germinated seeds caused by drought, shallow sowing, cobbly seedbeds or by mice excavations. Although this is only one relatively small reported investigation it implies that post germination factors are more important in reducing establishment, in contrast with the factors categorised by Aura (1975, Section 2.4.5).
The standard commercial seed processing procedure also implies that seed vigour is a limiting factor, as seed lots of high germination can be produced, and E.M.P. and methiocarb give protection to seedlings against some diseases and small pests. Additional control of millipedes and insects can be obtained by incorporating aldicarb or carbofuran granules in the seedbed (Durrant 1980). However although protection of seedlings may reduce "gappiness", faster emergence, the objective of the seed treatment used in the germination experiments in this investigation, is not encouraged.
Longden et al (1979) reported an extensive investigation into the effects of various priming, steeping and advancing pre-treatments. Some of these treatments were discussed in Section 2.2.8. None of the treatments gave significant responses in sugar yield compared with untreated seed as used in practice, despite a 30-50% increase in seedling weights during May and June in the field. This compares with a 100 fold weight difference between untreated seed and transplanted seedlings of multigerm varieties in June which resulted in a 28% (10 T/ha) increase in root yield (Scott & Bremner 1966).
The considerable amount of time and effort involved in treating the seeds (all involved many hours in solutions) with no guarantee of an improved yield resulted in Longden et al (1979) rejecting them as feasible alternatives to the standard procedure.
The advancing treatments, with or without GA3 solution, used in the germination tests in this investigation would probably be rejected on similar grounds even without field trials. However, the GA3 solution in the petri-dishes, although giving a smaller reduction in M.G.T. values and being less consistent in effect than advancing, allows GA3 solution to be in contact with true seeds. Contact with the true seed is necessary for acceleration of the physiological development of the germination process.
A method of allowing access of GA3, or another suitable growth regulator, to the true seed in 'the field is required. This could be achieved by mixing a relatively high concentration of GA3 solution with the E.M.P. steep in the standard processing procedure. A high concentration would be required, as the steep has to be of short duration (twenty minutes) to prevent mercury penetrating the true seed (Lindsay 1980, personal communication). Even if GA3 only penetrated the seed coat during the steep, it should reach the true seed on inbibition in the field.
An alternative method would be to incorporate GA3 in the pelleting material either in a layer close to the seed or spread throughout the coating (Longden 1975).
Germination tests and field trials with seeds treated with various steeping concentrations of GA3 solution or different formulations in the pelleting material would be required to assess the yield response and any disadvantages, e.g. incompatibility with the standard process.
Seedlings from GA3 treated seeds were found to be elongated and pale green by Scott et al (1972), but foliar application of GA3 had generally favourable effects (Garrod 1974). The root sink was increased early in the growing season, facilitating more efficient partition of the products of photosynthesis, but complex interactions with other endogenous growth regulators were occurring.
Another area where seed could be improved is in the seed production field. Battle & Whittington (1969a) studied factors affecting the maturity of true seeds on the mother plant (Section 2.2.5). Rainfall or irrigation appeared to have both beneficial and harmful effects. Washing out of inhibitors and seed advancing occurred (Longden, 1971, 1973, Section 2.2.8), but heavy rainfall probably associated with cooler temperatures, delayed maturity. Lower rainfall, probably associated with warmer temperatures, advanced the seed and hastened maturity.
Spraying seed crops with GA3 or other suitable growth regulators may accelerate-maturity and/or advance seed by allowing GA3 to contact the true seed on the mother plant. An early harvest of improved seed with less windshake losses could result, thus both root and seed growers could benefit. Experimentation would be necessary in this area.
Variation in rainfall on seed crops may advance seeds by different amounts, both on individual plants and in different seed growing regions. As seed is bulked and mixed in the processing procedure (Scott & Longden 1973) partial advancing by different amounts may explain some of the inherent variation in seed lots.
The potential uses of additional seed treatments can now be related to practicalities and costs. Seed processors would be unable to include Advancing or steeping procedures at a low cost to growers, unless a high demand existed, or if seeds of other crops could be treated simultaneously. Such a large scale requirement is unlikely to appear in the near future.
The grower however would only be interested in the yield response in relation to any additional costs of using treated seed. Assuming there are no other changes in variable costs, e.g. transport, gross margins would only be improved if every £1/ha addition to seed costs resulted in > 0.04 T/ha root yield. This calculation assumes that the price of 1 tonne of roots is £25.00 (NIX 1980). Treatment costs would probably be considerably more than £l/ha so that evidence of a reliable yield response is essential before a grower would contemplate using additionally treated seed. The large variation in sugar beet yields between years (Biscoe et al 1980, Scott & Jaggard 1978) shows that such evidence is difficult to obtain. The search for any method of improving yield without extreme practical difficulty or high costs must therefore continue.
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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]