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 Essay - sept/oct 2006
Seed system improvements
James C. Delouche
Professor Emeritus Mississippi State University
The idea of improving the seed system that I characterized as the ultimate delivery system in the previous essay appears to be a contradiction. If something is the ultimate how can it be made more ultimate? In terms of design - form and function - the seed is indeed the ultimate delivery system or nearly so with little need or scope for improvement. But, in terms of a vehicle for delivering one plant cycle into the succeeding generation along with additives and amendments, the seed is not perfect. It does have weaknesses that sometimes lead to catastrophic failures to delivery anything. Some seed weaknesses are related to our efforts to improve or diversify the taste, digestibility, nutritive value, and other organoleptic attributes of the products delivered, e.g., beans, rice, maize. The seed quality problems associated with the super-sweet green maize and some of the green bean varieties are familiar examples of seed weaknesses associated with improvements in the eating quality of the product which happens to be seeds.
Easy Level Improvements
Improving the seed system in a fundamental way, when feasible, is an exceedingly difficult task, requiring much time and effort. Some very practical, effective and relatively easy improvements, however, are available to correct weaknesses associated with poor seed production practices, mechanical abuse, adverse environmental stresses during maturation, harvesting and sowing. Many of these have been discussed in previous essays. Seed production in environmentally favorable locations has greatly improved the quality of vegetable, forage and specialty crop seeds. Informed management, better timing and greater caution in operations have overcome many of the seed quality problems in the major crops such as soybean, sorghum, cotton and wheat.
Modern, highly efficient seed cleaning and separating machines permit improvement of the quality of individual seed lots by removal of low density, small, diseased, mechanically damaged, insect infested and deteriorated seeds. For example, hi-tech color sorters are now used in maize, soybean, sunflower and large vegetable seed processing to remove discolored and other atypical seeds that are usually low in vigor and germination. Seed treatments of fungicides, insecticides and various biologicals are available, easily applied and very effective in covering-up mechanical damage, compensating for low vigor, and protecting seeds from the effects of some microenvironmental stresses in the soil.
Immediate Level Improvements
There are other seed system improvements of an immediate level available for some kinds of seeds that require more resources, knowledge, and /or expertise. These include moisturizing seeds to minimize mechanical damage and avoid imbibitional injury, the permeation of seeds with various phytoactive substances to control or direct germination and early seedling growth, the use of seed coatings to program seed performance, and the enhancement of seed performance by heat and mechanical treatments and, especially, by priming or osmoconditioning,
Fundamental Improvements
Fundamental improvements in the seed system have long been envisioned, discussed and debated with only marginal results. Most of them involve or would involve genetic changes either through conventional breeding or biotechnology protocols. The main difficulty has been to gain the attention of plant breeders. This has not been easy. Inattention to seed quality , a feeling that it is not as important as yield, or resistance to a disease, or a plea that the breeding objectives agenda is just too crowded to take in any probably quantitatively inherited seed quality attribute have been the most usual positions of plant breeders regarding seed quality improvements. If and when the attention of a plant breeder is gained, he or she has to be convinced that specific improvements are needed, that sources of variability for the improvement are available and that the seed improvement objective can be bundled with yield improvement, disease resistance, earliness, produce quality and other mainline breeding objectives. In some cases, a breeder just has a poor understanding of what seed quality is and its importance in crop production I recall my horror listening to a paper outlining the waste of photosynthate on the synthesis of indigestible soybean seed coat materials, sources of variability that would permit reducing the seed coat by half or greater, and the increase in yield that would be gained. In a private discussion with the author later, he admitted that he had not thought about the effect of thinning the soybean seed coat on seed quality, especially mechanical damage and field deterioration
I must hasten to add that some breeders have been receptive to ideas for inherent seed quality improvements and have given a lot of time to them including extensive trials. The ideas of reducing the field deterioration of soybean and cotton seeds by taking advantage of the hard seed variability in the species were given very adequate attention by respected breeders for several years. But, it eventually became quite clear that the low levels of residual hardseededness in cotton and soybean had been selected by lay and scientific breeders over many years for good reasons. Raising the level of hardseededness in the two crops lessened the effects of field deterioration but greatly complicated planting and stand establishment.
One of the problems in changing the inherent properties of seeds to improve their quality in the case of grain, grain legume, and oil seed crops is the effect of such changes on the end use of the product which is the seed. Developing a very thick, tough seed coat in cowpea, beans, chickpea to improve seed quality by reducing insect infestations might protect them against insects but greatly increase cooking time and the use of expensive and/or scarce fuel. Breeding green beans with more rapid and greater development of the beans than the pod walls would improve bean seed quality but at the expense of taste and consumption qualities. Similarly, going back to normal sweet maize or even field maize for green maize consumption is not a feasible solution to the seed quality problems of the super-sweet green maize.
Another obstacle to seed system improvements is that seed scientists and technologists tend to think of and approach them in very specific and restrictive ways relating to the seed and seed performance. There are holistic improvements underway in both the conventional and biotechnological arenas that could have enormously beneficial effects on the whole plant system including the seed and seed performance. Some example: resistance to diseases that affect the seeds and seedlings as well as the growing plant; salt tolerance; increased seed size and weight; drought tolerance, tolerance to other stresses such as heat, cold, limited aeration. The spin-offs of some of these works could resolve some of the most common and difficult stand establishment problems relating to micoenvironmental stresses in the soil.
Before beginning this essay, I spent the better part of one afternoon reviewing lists of applications for GM field testing in the U.S. with the hope that my optimism about the attention given to seed quality attributes by the biotech companies was valid. After searching the lists exhaustively, however, I had to admit my optimism was unfounded. There were only three trails out of several hundreds with a specific seed "phenotype" category: 2 with seed germination improved and 1 with seed quality altered, all in maize. Two additional references to specific seed quality attributes were : seed and seedling vigor in sugarbeet and resistance to storage pests in cowpea. Many of the trials, however, were concerned with drought resistant, salt tolerant, and stress tolerant phenotypes with the potential of holistic improvements as discussed above.
These things are certain
The easy seed system improvements have or are being made to increase the probability that the seed delivery system delivers what it is supposed to deliver and what the farmer-customer expects. Some of the immediate level improvements are being exploited by more seed suppliers for a larger variety of seed kinds. The more fundamental seed system improvements are not yet in the queue.
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