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 Main subject - sept/oct 2005
Seed Quality and Performance
James C. Delouche
Professor Emeritus Mississippi State University
One of the fundamental precepts of seed science and technology is that high quality seeds perform better than those that are of lesser quality. The main implication of this precept is that improving the performance of seeds in crop production is best achieved by concentrating on the development and production of high quality seeds and the maintenance of high quality through conditioning, storage, marketing and planting. No one can argue with this approach. It is demonstratively effective and efficient, but:
Is it the only approach to improve the performance of seeds?
The answer or response to this question necessarily involves recognition and analysis of several other relevant questions.
Are seed performance and quality essentially the same aspect?
Does high seed quality assure achievement of the desired seed performance?
Can the performance of high quality seeds be improved without significant change in their quality status?
Can the performance of lower quality seeds be economically and consistently improved?
Responses and/or answers to these questions, and perhaps a few others, are analyzed, discussed and addressed in this presentation.
Seed Quality and Seed Performance Are Not the Same!
Seed quality and seed performance are related and linked but are not the same aspect of seeds. Semantically, quality is an attribute or property that connotes superiority or excellence. Performance, on the other hand, is a dynamic aspect implying the execution of an activity, accomplishment of a deed, fulfillment of a claim, etc. While it is conceded that the term seed quality has long claimed a very broad meaning that embraces essentially all of the genetic, physiological and physical attributes of seeds, it can be and is argued that some aspects or attributes of seeds of great importance in crop production exceed the boundaries of quality and are best described and understood in terms of performance. This does not diminish the importance of seed quality but rather provides for a layer of expectations regarding seeds that are beyond the range of quality. The linkages and limitations of the seed quality and seed performance attributes are very evident in the following premises:
Seed performance is dependent on a high level of seed quality, but…
High seed quality does not guarantee they will perform as desired or expected.
Why the Current Emphasis on Seed Performance?
The basic biological functions of seeds are to serve as the repository of the inheritance of a plant population, e.g. a crop variety, and as the essential mechanism for the propagation and distribution of the population. Since seeds are relatively easy to produce, especially of grain and oil seed crops, and are multiplied rather than consumed in the production process, they were until relatively recently considered as an essential and crucial but rather inexpensive factor in crop production. Things have changed. Seeds have become both a delivery system and a property in our modern, mechanized, commercialized, genetically engineered crop agriculture. They are no longer the low cost item in the crop production budget. The high costs of seeds and associated technology fees demanded by the owners and producers of seeds are being countered by rapidly rising expectations of seed consumers, e.g., farmers, gardeners, regarding performance of the seeds in their operations. Additionally, global competition requires constant vigilance to minimize the costs of production through sound management and innovations that reduce or eliminate the labor and energy used for specific farming operations. Seed performance has long been viewed as critically important for obvious reasons by the seedlings industry that supplies seedlings of ornamental and vegetable crops of various ages and stages of development to home gardeners and producers of vegetables for the fresh market and for processing (canning and freezing). More and more producers of grain, oil seed and fiber crops, however, are now recognizing the potentialities of performance enhancing treatments of seeds for reducing the risks inherent in large scale, mechanized farming operations and the costs of production.
Seeds as Delivery System - The functions of seeds have enormously expanded from a repository of the plant population's inheritance and propagation to the delivery of insecticides, fungicides, micronutrients, phytohormones, biological products, herbicide safeners, genetically engineered traits for herbicide resistance, insect control, and a growing stream of other traits that improve product quality, produce specific biochemicals, and so on. Failures or deficiencies in seed performance, e.g., production of the desired population of uniform, healthy plants, upset the timing of the operations, reduce yields and the quality of the produce, and, of course, profits.
Seeds as Property - The most revolutionary change in crop agriculture in the last 100 years or more has been the change in the status of seeds of major crop and vegetable varieties from a commodity to an intellectual property. Plant breeders and seed producers, the owners of many of best varieties and hybrids of crops, can now fully recover the costs and a reasonable profit for their research and development work and operational efforts, and, thus, have the incentives, opportunity and resources to meet the demands of consumers relating to the quality and performance of the seeds they market.
Seed Performance Triangle + 3
The performance of seeds is determined by three linked and interactive components that constitute a sort of performance triangle: inheritance, physiological quality, and the environment. Inheritance is the genetic endowment received from the parents even for self-pollinated and vegetatively propagated crop varieties since except for mutant varieties the desired inheritance for both types is established through the mating of sexual parents. The environment for crop agriculture has three pertinent aspects: the edaphic that pertains to the soil or other medium for production; the biotic that consists of both helpful and harmful bio-forms, e.g., insects, microorganisms, weeds; and the climatic that comprises factors that support and/or control the growth and development of a crop variety, e.g., rainfall and water supply, temperature, sunlight. The physiological quality of seeds refers to their capability to perform their primal function of propagation which can range from zero to a full and unimpaired capability commonly described or characterized in terms of germination percentage and, more recently, vigor. Two other factors that influence seed performance need to be mentioned: the physical condition of the seeds (size, shape) and soil (crusting) and additives, i.e., products, mostly chemicals but including coatings, applied to or carried by the seeds. These determinants of performance provide both the reasons for and the means of improving or altering the performance of seeds.
Changing and/or Altering Seed Performance
Four main aspects of seed performance that can be altered, changed and/or improved are: germination, emergence, initial and early seedling development, and longevity or storage potential. Obviously, other seed attributes and additives, especially the inheritance component but also including some chemical seed treatments, can and do have season-long effects on crops. These are not considered in this presentation because it is felt that they are intended to improve crop performance, i.e., crop statue, architecture, maturation, etc., rather than seed performance.
Changes in any of the aspects of seed performance are designed to accomplish one or a combination of the following purposes:
To improve seed performance in terms of the percentage, speed and uniformity of germination and early seedling development, and the expansion or extension of the micro-environmental limits for germination;
To control seed performance in terms of the time of and conditions for germination;
To protect seed performance against micro-organisms, insects and micro-environmental stresses.
To assure seed performance to the extent possible by improving, controlling, and protecting it.
Improving Seed Performance
Many methods and treatments have been devised and are available for improving the percentage, speed, and uniformity of germination and early seedling development and for increasing the range of conditions for germination.
Physical Treatments - A variety of very familiar physical treatments have long been used to improve the performance of seeds. Removal of the hulls greatly improves both the percentage and rate of germination of dormant or residually dormant forage and pasture crop seeds of the grass family (Poaceae): e.g, high quality seeds of Cynodon dactylon, an important lawn and turf species, are marketed with or without hulls (lemma and palea); the hulled seeds are more costly but germinate much faster, i.e., perform better, than those with hulls. Scarification of seeds by mechanical means or with acids to release dormancy imposed by the seed coat or hulls and pericarp increases the percentage, speed and uniformity of germination of many important forage species of Poaceae and Fabaceae such as species of Panicum, Paspalum, Medicago, Trifolium, Melilotus, Lespedeza, and other genera. Acid delinting of cotton seeds not only produces a free flowing seed product that can be finely conditioned but also increases the speed and uniformity of germination and early seedling development which is very important in cotton production. Seed sizing and density grading facilitates precision planting and can have a great effect on the uniformity of emergence and initial seedling growth. One final very familiar example: peanut seed are shelled (hulls removed) and size graded to increase both the rate and uniformity of germination and emergence.
New machineries
Chemical Treatments - The most commonly used and powerful chemical for improving the speed, uniformity and percentage of germination and emergence is gibberellic acid, a phytohormone. It is used to counter the thermodormancy in lettuce seeds planted in the hot southwestern U.S. states for the winter market; it increases the percentage, rate and uniformity of germination of some lawn species such as Eremochloa ophuiroides; and more recently it is applied to seeds of some of the semi-dwarf rice varieties to increase emergence by increasing the length of the mesocotyl.
New chemicals
Physiological Treatments - Pre-germination of seeds by soaking in water or various solutions before planting to accelerate germination and improve uniformity has long been used to rapidly establish turf and conservation species along roadsides, renovated mining areas, and other places that have relatively steep slopes subject to erosion. Rice seeds are pre-germinated for water sowing to control red rice and other weeds that infest the aquatic environment of irrigated rice culture. The most recent, powerful and interesting treatment for improving seed performance is osmoconditioning or priming. Osmoconditioning or priming is the controlled hydration of seeds to a rather precise level that starts-up the metabolic machinery for germination and allows it to proceed to a point just short of resumption of active growth of the embryonic axis. Some of the processes are patented and the detailed procedures are held in close confidence by most of the seed companies that use priming to improve the performance of seeds. Priming increases seed performance in several ways: it extends the range of environmental conditions under which the seeds germinate, thus increasing the stand of plants obtained under micro-environmental stresses; it increases the speed and uniformity of germination; and releases residual or induced dormancies such as some photo- and thermo-dormancies; and it increases the uniformity of germination, emergence and early seedling development, critical for producing a crop that matures uniformly and on schedule.
page 2 ->> Seed Quality and Performance
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