|
 Essay - sept/oct 2004
The seed performance triangle
James C. Delouche
Professor Emeritus Mississippi State University
The performance of seeds is determined by three linked and interactive components that constitute a sort of performance triangle: inheritance, physiological quality and 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, recently, vigor.
The environmental component of the seed performance triangle was considered in some detail in the March/April and May/June, 2004, issues of SEED News under the title "Seed Quality is Not Always the Problem." Additionally, it was implicated as the cause of the crop failure, rather than seed vigor, in one of the civil litigations related in the first part of this essay on Seed Performance in the May/June issue. For the remainder of this multi-part essay, therefore, the environment will be brought into the discussion only to illustrate some of the linkages and interactions with the inheritance and physiological quality components.
Inheritance
Long, long ago when I was in high school in Louisiana, USA, and an enthusiastic member of the 4-H club, I decided to enter a maize yield contest as my club project and was persuaded by the 4-H advisor to plant a new type of maize he called a hybrid. He supplied the hybrid seeds and helped me plant a 1 acre plot in a field close to the road so farmers, traveling on the road "could easily see the new type of maize." My plot of hybrid maize began to attract a lot of attention when it reached the tassel and silk stage and even more attention as it developed and matured and the potential of an extraordinary yield became evident. The many farmers who stopped to look closely at the plot expressed astonishment at its apparent vigor, dark green color, and remarkable uniformity in plant height, ear size and position. They all assured me that I would easily win the yield contest. But, I didn't win. We did not even harvest the plot because by the time our farm work schedule permitted harvest the "weevils" and "rot" had invaded the ears and turned the "yield" into grain dust and rotted kernels. I was deeply disappointed, the 4-H advisor was embarrassed, and my father resolved to keep hybrid maize far away from our farm. Other "early adopters" of hybrid maize in the hot and humid state of
Louisiana had a similar experience: a great maize crop was produced but a poor or no crop at all was harvested. Several months later a specialist from the State Extension Service offered this explanation for disastrous experiences with hybrid maize: Louisiana had only a marginally favorable climate for maize production to which the hybrid variety was not well adapted; the husks did not enclose the tip of the ear providing the weevils and grain rot microorganisms with easy access to the grain; harvest was delayed too long providing ample time under very hot and humid conditions with frequent rain for the weevils to infest and consume most of the grain and microorganisms to rot the rest. Progress, however, was only temporarily halted. A few years later when I was in college my father planted a different and much better adapted hybrid variety with excellent results and never planted open pollinated maize again except for a garden variety especially good for green maize consumption.
This tale of a disappointment contains several lessons that are pertinent to the present discussion: 1) the good inheritance of a crop variety, even an elite, high-tech inheritance, does not guarantee superior results; 2) favorable environmental conditions and good management are necessary for realization of the heritable potential of a variety; and 3) good inheritance combined with a non-limiting environment and appropriate management is an unbeatable combination that can produce extraordinary results.
Scientific plant breeding began early in the 20th century with the rediscovery of Mendel's principles and rules of inheritance. It was soon recognized that improving the inheritance of crop varieties by systematic and rigorous application of genetic science was perhaps the most accessible, economical, and powerful means of increasing their productivity and adaptability. Many of the incremental and most of the dramatic advances in the productivity of crops during the last 100 years have been achieved through the development of varieties with superior traits adapted to different environments and levels of inputs. Incremental improvements have included changes in maturity, resistance to disease, higher competitive capacity, better quality and acceptability of the product and so on. Arguably, the first truly dramatic improvement was the development of hybrid maize followed in time by the development of hybrid varieties of other grain and fiber crops such as sorghum, pearl millet, rice, cotton and of many vegetables. During the 1960s another cycle of truly dramatic improvements in crop productivity was spawned by the development of the green revolution varieties of wheat and rice. Most recently, dramatic improvements in crop varieties have been and are being achieved through the application of biotechnology especially the transfer of desirable traits from mostly obscure and non-economic species into improved crop varieties, i.e., transgenic or genetically modified varieties.
The development of scientific plant breeding greatly accelerated the transition of crop agriculture from a species basis to a variety basis. Farmers began to plant specific varieties of wheat and rice and other crops rather than the local land race. It was soon realized, however, that the benefits expected from changing to a new or different variety were wholly dependent on obtaining an authentic supply of the seeds. Since many crop varieties cannot be identified on the basis of the appearance of the seeds, means and procedures other than or in addition to examination of the seeds had to be developed to assure farmers that the seeds they acquired for planting a desired variety were authentic. The assurance needed was provided through the development of the well-known seed certification scheme or system that has played a crucial role in the development of modern, variety based agriculture.
Several weeks ago I attended the annual joint meetings of the Association of Official Seed Analysts and the Society of Commercial Seed Technologists that I had not attended for 4 or 5 years. I was astonished and a little confused by the complexity and sophistication of the laboratory techniques and analyses now required to satisfy quality assurance protocols and regulations relating to the genetic identity of crop varieties. There was an all-day genetic technology workshop, herbicide, immunoassay, electrophoresis and PCR working groups, genetic technology and ISTA GMO task forces, and, of course, a meeting of a committee I recognized - the cultivar purity committee. Interestingly, analysts are now being examined, registered and/or certified in genetic technology and related analyses as well as in traditional purity and germination testing. All of this science and technology was somewhat overwhelming to this "retired" seed technologist who completed his Ph. D. in Botany at Iowa State University and entered obligatory military service for 2 years without knowing that Watson and Crick had just published on the structure of DNA, the double helix. Nevertheless, I was and am impressed by the skills and confidence of modern genetic trait analysts and their determination to keep abreast of the incredibly sophisticated varietal products of biotechnology. And, I would be remiss to not state that I am much comforted by a strong belief that despite current controversies the powerful combination of biotechnology and traditional plant breeding will fully meet the challenge of providing adequate and nutritious food and feed to a still increasing world population from a diminishing crop land base.
The next and final installment of this essay on seed performance will deal with physiological seed quality the third angle of the performance triangle.
|
|
............
|
