Text from a technical feature, written by Hugh Poths,
sponsored by HorTIPS
and kindly provided by The Vegetable
Farmer which is an ACT Publication.
Seed viability and plant
establishment
Vegetable crops need to establish quickly and evenly to reduce the risk of problems beneath the surface and to begin the process of growth towards a high yield of uniform product. Good seed quality is therefore one of the most important factors in the production of profitable crops both in the direct drilled and raised plant situation.
The past few seasons have seen an increase in pressure on our production systems. Not only is achieving real financial gain more of a challenge but apparent variation in seasonal trends, together with extremes of weather, have increased the risk of problems through a crops life. This has raised further concerns over how the British industry can continue to maximise its efficiency and it is becoming more necessary to look at complete production cycles to identify and improve the weakest link in the chain.
Andy Richardson of the Allium and Brassica Centre states one of the best examples of this thought process. “The bulb onion industry has reduced plant populations consistently over the past five years in order to maximise the marketable proportion of the crop in the higher value 60-80 mm size range. It is essential that the correct number of plants is established per square metre in order to optimise both yield and quality. Too few and thick-necked, coarse bulbs will result: too many and bulbs will tend to be small and therefore of lower value. Historically we have relied upon germination counts at both 7 and 14 days to give us some idea of seed quality. However in adverse seedbed conditions, particularly of the past two springs, seed lots with similar or identical germination figures have performed vastly differently in the field. It would appear therefore that under some conditions standard germination results do not provide the whole picture and that the development of a meaningful, rapid, cost effective test should be seen as essential to profitability.”
This principle applies to all our crops. Variation in uniformity of a group of plants at the seedling stage can only be accentuated as those plants grow. This is especially the case if there is any limitation of availability of inputs such as fertiliser or water for which the stronger plants will be better able to compete. Differences in growth are likely to increase and we find that not only is total yield affected, but also as mechanisation becomes more important, both in harvesting and preparation, so an increased level of uniformity is needed to maximise efficiency. Raised brassica plants can also suffer in this way, even when growing conditions appear favourable, as a high percentage pack of specific head size is needed to maximise returns for the crop. The development of cauliflower hybrids has enhanced crop performance considerably but any reduction in seed quality is now even more noticeable.
Seed Production
Seed production is also becoming more of a challenge as customers’ quality requirements become more specific and, at the same time, volumes for particular markets diminish making successful targeted production of such an item increasingly difficult to achieve. Financial pressures also exist within seed companies.
Plans and budgets are created on the basis of past production experience and expected sales but variation in climatic conditions means that potentially every seed crop grown can give a different result and each has to be handled separately. Each lot is fully assessed and is normally monitored from harvest through cleaning, separation and other processes to realise its best potential.
The most important measure of potential seed performance is the standard germination test, which is carried out to a formal set of rules specific to each crop, and defined by the International Seed Testing Association. This system ensures that results are consistent and repeatable between testing centres and allows commercial decisions to be made regarding the usefulness of each seed lot. The test consists of growing a randomly selected sample of seed, in a controlled environment and recording growth at two points in time. The final figure gives the potential of the lot while the interim count, is often used to indicate the ability of the seed to grow in more difficult conditions. The time taken for germination to occur suggests a level of viability as well as indicating likely uniformity of germination but in practise this data is not always reliable when compared to actual field performance.
Seed is often set to grow in conditions that are less than ideal. Timing of sowing is programmed for continuity and, either indoors or outside, temperature levels or water status are often different to the ideal circumstances of a laboratory. Pests and diseases lurk in readiness to attack and chemicals, applied to give protection at some stage in the crops life, can upset development. While germination figures indicate the potential of the seed, its relative ability to cope with difficult conditions can be defined as vigour.
Seed Tests
Research has been carried out to allow us to understand more of the ability of seeds to grow in various conditions. Inevitably this has been carried out in a laboratory environment. Some of this work, however, can relate to field situations enabling prediction of relative performance to be made and allowing decisions to be made on the usefulness of particular lots. Specific crop tests have been developed for seed of peas, beans, carrot, and lettuce with a general assessment of most vegetable crops possible by using a controlled deterioration test. The average level, as well as the uniformity of vigour can be assessed for certain crops and, although under no obligation to provide data, seed companies are trying to give guidance on this subject where possible.
The bean test is carried out by assessing the proportion of complete cotyledons stained by a chemical with special properties, which is called tetrazolium chloride. A pea test is based on the concentration of salts released from the seed into a sample of water, which is then tested for electrical conductivity. The better lots of seed tested by these two methods are preferred for earlier drillings when conditions are more challenging and others are used when there is less risk.
A carrot vigour test involves measuring the seed embryo length and recording variation within a lot. The higher the level of uniformity the more likely that a high pack out, at a specific size, will result at harvest. The quality of lettuce crops may be predicted in a similar fashion by using a slant board test to measure seedling root length.
Exposing them, under controlled conditions, to the two most important variables that influence deterioration can test the viability of most vegetable seed types. This test is an ageing technique that records the germination potential of seed before and then after treatment at high temperature and moisture. The resultant vigour comparison gives an indication of likely storage and field performance and is called the controlled deterioration test.
The quality of seed when measured in a laboratory enables commercial decisions to be taken by those responsible for maintaining standards for the industry. It is still necessary to continue the development of techniques to allow us to minimise the risks involved in growing that seed especially in more challenging conditions.
Rae Cook of Elsoms Seeds says “Seed quality is an essential factor in the start of any crop. We are always looking at ways to improve seed quality in production, processing and storage conditions in order to achieve the best systems and supply our customers with the best possible advantage.
Samples from each seed lot are tested for purity and germination in our licensed seed testing laboratory and we use a range of technologies to provide crop enhancements such as priming, addition of beneficial micro-organisms as well as conventional crop protection seed coatings in our own application machinery at Spalding.”
At a time when seed quality issues are so important it is realistic to remember that we are working with a delicate living organism that should be treated with respect. To achieve optimum performance from new genetic material we need to continue to research and apply methods that will help towards the target of growing one thousand healthy and uniform plants from a thousand seeds.