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 Essay - jan/feb 2005
Seed Performance: Addendum
James C. Delouche
Professor Emeritus Mississippi State University
About 6 months ago I did a bit of thinking and made some notes for an extended, three-part essay on the general subject of seed quality and performance. I did the first two parts under the titles Seed Performance and Seed Performance Triangle about as planned. But, as I was actually writing the third and final part of the essay under the title Improving and Enhancing Seed Performance for the November/December issue of SEED News I was so strongly attracted by an editorial in another seed trade magazine titled The End of Seed Quality that I literally abandoned my notes and plan for a critique and commentary on the editorial. The issues and points relating to seed performance that I had planned to discuss were barely mentioned much less discussed. So, I decided to do this addendum to more-or-less finish my discussion of seed performance in the way I planned more than 6 months ago.
In the last issue before I got diverted by The End of Seed Quality editorial I posed these questions: Are seed performance and quality essentially the same attribute? Can the performance of high quality seeds be improved without significant change in their quality status? I then related several examples of improvements in performance without a change in quality, e.g., simple priming of lawn grass seed to accelerate seedling emergence and establishment, gibberellin treatment to improve emergence of semi-dwarf rice, and with a change in quality status, e.g., gibberellin treatment to release dormancy and increase both the rate and percentage of emergence. It was at this point that my attention was diverted from the issues of seed performance/seed quality to commentary on the editorial. Thus, I will now return to where I was before the diversion.
Seed Quality Improvements
During my retirement year (1995) I co-authored (with E. Cabrera and B. Keith) a bulletin on Strategies for Improving Physiological Seed Quality. We reviewed the research on seed quality done by staff and graduate students in our laboratory and relevant research of other workers at other institutions to develop what we termed "a conceptual framework for seed quality related research and development." Four strategies for improving seed quality were identified and discussed: maintenance, upgrading, genetic, and enhancement. Proper implementation of any one or combinations of the strategies improves seed quality and performance. The maintenance and upgrading strategies involve such things as timely and careful harvest, proper drying and aeration, favorable storage, and rigorous conditioning to remove contaminants and defective seeds, increase average seed density and size uniformity. These strategies are being fully and rigorously implemented by most of the large seed companies. They closely supervise seed production, harvesting and drying, store seeds in conditioned warehouses, and use a full array of precision seizers, density separators, color sorters and automated treating and packaging systems to market seeds of most major crops that are very high in germination and vigor and essentially impeccable in appearance. Recognizing that for some kinds of crop seeds, e.g., maize, soybeans, major seed companies have pursued improvements in production, conditioning, storage and packaging to the point of no significant return value, the author of The End of Seed Quality editorial concluded or speculated that there was no scope for further improvements. In my commentary on the editorial, I stated that I had no argument with the author's conclusion with the stipulation that it was probably applicable only for maize and soybean seeds in the U.S. market. This leaves many opportunities for improvements in seed quality through the maintenance and upgrading strategies for many other seed kinds and in many other countries. And, it does not preclude improvements in the performance of even the highest quality seeds in the most modern situations through implementation of the genetic quality and quality enhancement strategies.
Improving Seed Performance
The genetic and enhancement strategies can and have improved seed quality with concomitant improvements in seed performance and seed performance without significant effects on intrinsic seed quality. There has been considerable work on improving seed quality thorough breeding for seed types that resist mechanical abuse and field and storage deterioration which would not only facilitate implementation of the quality maintenance strategy but also significantly extend its limits. The genetic approach can and has produced seed types that perform better and more consistently in terms of germination and emergence under temperature, moisture and salinity stresses and mechanical impedance. It must be conceded that it is difficult to disassociate such improvements in performance from improvements in intrinsic physiological quality. Seeds of variety A, for example, perform 100% under favorable conditions but very poorly in a moisture deficient soil, while those of variety B perform very well under the favorable conditions and nearly as well in a moisture deficient soil. Since seeds of both varieties perform at a maximum level under usual or average field conditions it might be concluded that although performance differs under severe stress there is no real difference in seed quality. But, the definition of seed vigor, which is certainly an important attribute of seed quality, includes performance under a wide variety of field conditions. Breeding for improved emergence and stand establishment under stresses does, therefore, involves significant improvements in seed quality. Indeed, I am unable to think of a genetic trait that could improve the performance of seeds that would not also improve their intrinsic quality. This confounding of seed quality and performance, however, is of little interest or consequence to either producers or consumers of seeds. They are interested in results not categories. Considering the increasing costs of the "seed input" in crop production, farmers want and expect seeds to perform at the near maximum level.
The enhancement strategy for improving seed quality can be separated into two components: one that improves seed quality and performance and one that essentially improves performance. The gibberellin treatment for improving emergence of the semi-dwarf rice varieties is an example of the latter. I also consider osmo-conditioning or priming as a performance enhancing rather than quality enhancing treatment. Most of the fungicidal and insecticidal seed treatments can also, very significantly, improve seed performance in terms of crop establishment without any change in intrinsic seed quality. Performance is the desired result so farmers do not object to the substantial costs for the added value.
Seed coatings are among the most interesting and potentially beneficial treatments for enhancing seed performance. Their most important use, of course, has long been in fungicidal and insecticidal seed treatments. Nearly 40 years ago, however, several Canadian researchers used a three-layer coating on wheat seeds to permit fall planting of spring wheat. Polymer science was then not so well developed so there was little progress. Twenty-five years ago rice seeds were coated with calcium peroxide to provide oxygen for germination and emergence in "water" seedings. During the 1980s and early 1990s several of my students (including the technical editor of SEED News) demonstrated that coating soybean seeds with a hydrophobic material such as linseed oil or lanolin maintained germinability of the seeds under moisture deficit and flooded conditions and reduced imbibitional injury in very wet, cold soils.
Advances in polymer science, especially temperature-activated polymers, have produced some very innovative applications of seed coatings. Maize seeds coated with appropriate temperature-activated polymers can be planted into cold soils a month or so sooner than the normal planting date. This greatly expands the window for planting maize and lessens the concentration of work during critical periods in spring. Another coating is marketed for inter-planting soybeans into wheat for improved double or relay cropping. It is interesting that one of my colleagues, long deceased, had limited success in the early 1980s using so-called hardseeded lines of soybeans for fall planting into wheat. It seems to me that there is considerable scope for using seed coatings to regulate the time of germination and emergence not just in temperate climates with cool and warm seasons but also in subtropical and tropical areas that usually have wet and dry seasons.
Surely we are not at the end of seed quality. Appearance, even high germination and vigor are not the only determinants of seed performance. There are powerful methods for improving the quality and performance of seeds that can be and must be explored, developed and exploited after the production, maintenance and conditioning procedures are exhausted.
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