An Introduction to Genetic Delivery Systems in the Pacific Northwest

Transcription

1 1 An Introduction to Genetic Delivery Systems in the Pacific Northwest 11 Development of a Specialized Seed Industry in the Pacific Northwest The first major seed production industry began to develop in the eastern and central regions of the US in the late 1800's to supply the growing nation with seeds of vegetables and flowers But by the early 1900's, vegetable and flower seed production enterprises had in large part migrated to California to take advantage of the favorable climate in that state The world's current leading seed industry was developed to supply hybrid seed com in the 1930's and is located in the Midwestern US This highly specialized industry evolved to supply farmers with seed of the newly developed com hybrids Because of the genetic nature of these hybrids, farmers could not save seed and therefore, had to purchase new seed each year in order to grow the crop On the other hand, seed industries that focus on the production of self-pollinated crops tend to be small regardless of the number of acres grown For instance, wheat production is an extensive, world-wide enterprise, yet wheat seed production is a surprisingly small endeavor Since wheat is a self-pollinated crop and commercial cultivars are not hybrids, many farmers tend to save seed after the initial purchase of a new cultivar release Forage seed crops were originally produced as a by-product of forage production in the Midwest Grass seed crops were introduced as early as the 1920's as an alternative crop for the southern Willamette Valley During the 1930's and 1940's, farmers in the Pacific Northwest and elsewhere began planting greater acreage of forage grasses and legumes solely for seed production Prior to World War II, farms in the Willamette Valley were more diversified and smaller than farms today Most north valley farms were located on rich, loamy, and well-drained soils ideal for diversified crop production In contrast, south valley farms situated on the broad terraces between Albany and Eugene were located on poorly drained clay soils, and these farms could not compete with their valley counterparts in the production of grain, vegetable, and fruit crops Ryegrass was especially well adapted to the wet soils and soon became an important crop Grass seed also established itself as an excellent alternative crop for the highly erodible foothill soils found on the valley's eastern flank Since 1940, the industry has made steady growth, with many national and international seed companies located in the Willamette Valley The newly emerging forage seed industry in the Pacific Northwest began to rapidly develop in large part because of the favorable climate and the evolution of specialized management practices to take advantage of this climate This evolution resulted from the cooperative efforts of individual seed growers, industry suppliers, the region's universities, and the USDA In the post-world War II period, the growing affluence of the USA and other nations in the industrialized world led to an increased demand for grass seed for lawns, golf courses, and other recreational fields and facilities As this demand increased, plant breeders at several universities and in companies began the development of grass cultivars specifically bred for use in turf applications Forage and turf seed production industries that developed in the Midwest had largely

2 2 relocated to the Pacific Northwest by the 1960's The only significant US grass seed industry still extant outside of the Pacific Northwest is found in Missouri, where sizeable production of tall fescue can be found Even though the seed production moved to the Northwest, the primary consumers of grass seed crops remain in the Midwest and in the eastern US Thus, these seed crops are being produced outside of their area of principal adaptation or use, so special procedures must be followed to prevent genetic shift, a genetic change that will be discussed later in this chapter Many types of the vegetable and flower seed are now produced in the Pacific Northwest Idaho has for many years been the leading US producer of sweet com seed The primary reasons for the development of this diversified seed production industry in the Pacific Northwest: Dry summers Mild and wet winters Great variety of soils over short distances High seed quality High dependable yields Production of turfgrass seed in the USA is now second only to com seed production in economic value, and the majority of this production takes place in the Pacific Northwest The Pacific Northwest has long been a national and world leader in the production of high quality, cool-season grass seed The region's seed growers and seed companies have been able to adapt to a rapidly changing business and regulatory environment Grass seed crop acreage in Oregon is at an all-time high and these crops have ranked among the top five most valuable agricultural commodities in Oregon for the past decade The continued success of the seed industry will be predicated by its ability to recognize new opportunities and to address present and future problems The urban-agriculture interface and the conflicts that arise where the farming community meets the non-farm population might very well be one of the greatest challenges facing the region's seed industry Prime farm land has been lost at an ever increasing pace to housing and industrial development despite restrictive land-use policies This competition for land is a cause for concern among seed growers and for seed companies seeking contract acreage At the same time, other traditional crops in the Willamette Valley such as wheat and others have declined in acreage due to faltering profitability Other crops have been displaced by pest problems or loss of processing facilities 12 Seed Production is a Specialized Form of Crop Production Seed production is the activity, science, and technology that increases the availability of high quality seed at the lowest environmental and economic cost Seed crop income depends more on the quality of production rather than on the quantity of seed produced Quality control is very important Unlike general crop production, it is imperative that seed to be used as planting stock is free from weed or other crop seed that may contaminate the seed production field and must be of the proper seed class Isolation is

3 required to prevent unwanted fertilization of the crop by foreign pollen of unlike cultivars ofthe same species or by pollen of closely related (interbreeding) species The isolation distance between seed fields depends on the crop species and the mode of pollination Isolation distances range from only a few feet for many self-pollinated crop species to over five miles for some cross-pollinated species The land history of the proposed seed production field must be known since the same cultivar must not have been recently grown in order to prevent contamination by volunteers The soil should be free from seeds of objectionable and otherwise hard to control weeds Seed production enterprises generally have much higher costs of production than the costs typically encountered in crop production of the same species These higher costs result from the specialized management practices that seed growers must employ to maintain high seed quality and seed yield Seed crops often have unique pest and fertility management problems Harvesting and post-harvest management practices often differ significantly from general crop production Seed conditioning is an important step in obtaining clean, high quality seed that is readily marketable from the relatively dirty seed brought in from the field after harvest Seed conditioning includes seed cleaning, size grading, seed treatment, and packaging activities 3 The quality control in seed production consists of two major components; seed certification and seed quality testing Seed certification is a voluntary program dedicated to maintaining the genetic purity and identity of a cultivar while increasing the quantity of seed that is available Seed quality testing involves the laboratory testing of seed samples to determine whether sufficient quality is present in the seed lot to meet the requirements of the seed certification agency, and farmers and other consumers Seed quality tests in common use include: Seed germination Purity - conducted to determine the presence of other crop seed, weed seed, and inert material Seed health - detect presence of plant pathogens or insects Seed vigor - a measure of field emergence potential Seed moisture content -important for maintaining quality in storage 13 Crop Genetic Resources Seed production is an essential component of genetic resource development and genetic delivery systems New favorable genetic combinations are packaged by plant breeders and are multiplied through seed production while maintaining genetic integrity and seed quality Even the act of collecting seeds in the wild from native plants and growing these

4 4 plants constitutes a fonn of plant breeding The economic and environmental sustainability of crop production systems depends on the development and delivery of planting stock that maximize field perfonnance, crop quality, and pest resistance Crop breeding is the systematic improvement of plants to meet human needs Crop breeding began with the original domestication of crops from their wild ancestors These improved crop populations are known as landraces and are endemic to a particular region The early domestication of crops resulted in: Larger plants Larger seeds More rapid and unifonn seed gennination Improved palatability Loss of defensive structures -hairs, spines, and thorns Annual habit and self-pollination Early domesticators of crop plants achieved these important advances by selection Selection is a method of crop improvement that involves recognizing plants having superior characteristics and using their seed to plant the next generation Landrace populations have been selected and cultivated over many generations by local residents The breeder must have genetic variation in order to improve plant characteristics Crop breeders identify new favorable genetic combinations that lead to improved perfonnance and incorporate these traits in the development of new cultivars A cultivar (cultivated variety) is a subdivision of a kind (ie wheat, alfalfa, soybean, broccoli), which is distinct, uniform, and stable Cultivars are the end-product ofthe crop breeding program's efforts In addition to selection, crop breeders employ several major methods of crop improvement depending on species and breeding objectives Achievements of crop breeding programs include: Increased yield Resistance to pests Improvement in quality (ie taste, color, aesthetic factors) Adaptation to mechanical harvest Adaptation to management practices (ie irrigation, fertilizers) Crop breeding depends on the identification and incorporation of traits that can be transmitted from the parental generation to progeny (heredity) DNA (deoxyribonucleic acid) is a chemical, which is composed of the characteristic sequence of nitrogenous bases fonning the foundation of the genetic code Each sequence of bases that contains infonnation for the production of a specific protein is known as a gene The gene is the fundamental unit of inheritance and is located on the chromosome The complete

5 genetic composition of a plant is tenned the genotype The genotype is a combination of genes that interact to detennine the plant's perfonnance potential Germplasm refers to the potential genetic combinations or genetic variation within a crop species but is also used to denote specific seed stock or clonal material containing valuable genetic combinations Crop breeders and geneticists collect gennplasm from all parts of the world in the hope of finding new genetic combinations This gennplasm may be in the fonn of landrace populations still cultivated today in developing nations or as wild plants growing in the area of origin of the crop The genetic variation present in the gennplasm serves as the basis for the development of new cultivars Gennplasm can also be obtained by crop breeders from several repositories including the National Clonal Gennplasm Repository in Corvallis and the National Seed Storage Laboratory in Ft Collins, Colorado Both collections are maintained by the USDA Several regional plant introduction facilities also maintain gennplasm collections Genetic variation that does not exist in nature can be created in the laboratory Chemical (ethyl methane sulfonate) or radioactive (gamma rays) agents can be used to induce genetic mutations that may include favorable genetic variation New genetic combinations can also be created through genetic engineering DNA from a donor plant cell is selectively removed using restriction enzymes and is transferred to another plant cell, thereby incorporating a gene that had not previously been present in the recipient cell 5 14 Genetic Delivery Systems Crop breeders develop new cultivars that have characteristics, which are superior to the cultivars that are presently available However, the quantity of seed or clonal materials produced by crop breeding programs is not sufficient to serve as planting stock for crop production The quantity of planting stock must be multiplied while maintaining the essential characteristics and genetic identity of the cultivar A cultivar may be propagated by seed (oats, cabbage, tall fescue) or by vegetative propagules such as tubers, cuttings, rootstock, etc Examples of crops propagated by vegetative propagules include potato, sugarcane, and mint Seeds are the primary genetic delivery system for improved crop cultivars The reasons for the dominance of seeds as a genetic delivery system are that seeds are: Small and hardy Convenient to store and transport A repository for heritable traits Figure 11 shows a diagrammatic representation of a seed-based genetic delivery system Geneticists develop or identify new genetic traits which are incorporated into new

6 6 cultivars by the breeder It is at this point that the seed grower is involved in the genetic delivery system, multiplying the quantity of seed until the amounts desired by crop producers and consumers are attained Genetics! Crop Breeding! Figure 11 A diagram of a seed-based Seed Production genetic delivery system Crop Production!! Consumer 15 Cultivar Maintenance A cultivar is a subdivision of a kind which is distinct, uniform, and stable A kind is a group of subspecies, or cultivars, collectively known by a common name For example, wheat, alfalfa, and soybeans are considered to be kinds The main features of a cultivar includes: Distinct --Can be differentiated by one or more identifiable, morphological, physiological or other characteristics, from all other cultivars of public knowledge Uniform -- Variation in essential and distinctive characteristics is describable Stable -- Cultivar will remain unchanged to a reasonable degree in its essential and distinctive characteristics and in its uniformity when reproduced or reconstituted as required for the different categories of cultivars ill order to maintain the genetic integrity of a cultivar while increasing the amount of seed, we need to know what type of cultivar is being grown Several types of cultivars are outlined below: 0 Line --Consists of one or more self- or cross-pollinating genotypes and single-line apomicts For example, this includes wheat, soybean, and Kentucky bluegrass

7 Clonal --A vegetatively propagated cultivar For example, by cuttings--because of advancements in somatic embryogenesis systems, we now can produce synthetic seeds Multiline --Consists of two or more near-isogenic lines of self-pollinating crops that are similar in most characteristics, but differ in a limited number of describable physiological or morphological characteristics The lines are grown separately and composited to form the Breeder seed Examples include oats and wheat Open-pollinated -- Consists of cross-pollinating plants selected to a standard which may show some variation, but can be differentiated from other cultivars Examples include 'gold bantam' sweet com and crested wheatgrass Synthetic -- Seeds are produced by interbreeding a population of inbred lines, clones, or other populations of cross-pollinating plants Two types of synthetic cultivars are produced: first generation synthetics and advanced generation synthetics Examples include tall fescue, orchardgrass, alfalfa, and most of the important forage and turf grasses and legumes grown for seed in the Pacific Northwest The genetic delivery system for a first generation synthetic cultivar of creeping bentgrass is depicted in Figure 12, while an advanced generation synthetic's delivery system for Chewings fescue is shown in Figure 13 7 Parental Clones Poly Cross Nursery! Figure 12 Breeding diagram for Progeny Tested Penncross creeping bentgrass, a first Space Planted Nursery generation synthetic cultivar! Syn 1 Seed Hybrid -- There are two types of hybrids: An FI hybrid -- Consists offi progenies of controlled crosses between: two inbred lines, two single crosses, a single cross and an inbred line, or two clones, cultivars, or species Examples include sorghum, com, tomato, and cabbage F2hybrid -- Derived from the progeny of the hybrid FI generation An example is tomato Hybrid cultivars cannot be reproduced from seed ofthe hybrid generation Other plant types include mixtures, blends and common seed These are not considered to be cultivars Apomixis is the production of seeds and vegetative propagules in parts of the plant

8 8 nonnally concerned with the sexual process, but without the fusion of gametes Agamospermy is apomictic seed production Kentucky bluegrass produces seed by agamospenny The main features of apomixis include: substitution for meiosis and fertilization, found in the flowering parts of plants, and occurs without fusion of gametes 28 Parental Clones Progeny Tested Syn 1 Seed Maintained Vegetatively Breeder Seed Syn 1 Seed -! Foundation Seed Syn 2 Seed Figure 13 Diagram of an advanced synthetic cultivar of Chewings fescue Certified Seed Syn 3 Seed The progeny of apomictic plants are unifonn and are identical to the parent plant Pollination mayor may not be required in apomixis for the successful production of seed The genetic composition of a cultivar can change in the seed multiplication process A cultivar can change over time during seed production as a result of: Mutations Late segregation Out-crossing Early harvest Mechanical mixture Genetic shift Genetic shift is a change in the component makeup of a crosspollinated cultivar as a result of environmental selection pressure Genetic shift can be caused by photoperiod, winter temperature, disease, and competitive ability (natural selection) Genetic shift is a problem for open-pollinated and synthetic cultivars when the seed is produced outside of the area of adaptation Genetic shift should not be confused with genetic drift, which is the random change in the genetic constitution of small isolated populations

9 9 Several procedures are effective in preventing genetic shift: Breeder seed produced in the area of adaptation Limit the number of generations grown out of the area of adaptation (3 or less) Limit the life of the stand (4 to 5 years) An example of genetic shift involved the production of red clover seed Kenland red clover is resistant to southern anthracnose, which is a disease found in Kentucky, Ohio, and Tennessee (area of adaptation), but does not occur in the seed-producing regions of the west In the west, there is a shift toward non-resistant plants in the populations, so only 2 generations of red clover seed increase are permitted from the Breeder class seed The constituent makeup of a cultivar can also change in ways other than genetic shift The procedures that need to be followed to prevent changes that might take place in the genetic integrity of the cultivar include: Same cultivar not grown recently on that land Remove off-types Observe isolation distances Start production with Breeder seed Avoid mechanical mixtures These procedures form the basis of the seed certification system 16 Seed Certification What is seed certification? The purpose of seed certification is to maintain the genetic purity and identity of a cultivar while increasing the quantity of seed that is available Plant breeders develop new cultivars that have yield, disease, or quality characteristics that are superior to the cultivars that are presently available Through the certification process, these small quantities of Breeder seed are increased to the quantities that are required to meet the needs of the agricultural industry Personnel working in a certification program monitor the seed multiplication process to verify that the seed meets the criteria required to protect the genetic identity of the new cultivar Seed certification is a voluntary program: The grower agrees to abide by the standards set forth by the certification agency Both public and proprietary cultivars can be certified About 10% of US seed crops are certified Most of the non-certified seed is comprised of com, soybeans, and small grain cereals Between 50 and 60% of Pacific Northwest seed crops are certified This seed is largely destined for foreign and domestic export markets Therefore, maximum genetic purity and seed quality is desired

10 10 Four seed classes are generally utilized in the seed multiplication process controlled under the US seed certification scheme: Breeder seed --Breeder seed is marked by a white tag The production of Breeder seed is supervised by the plant breeder Foundation seed -- Foundation seed is also denoted by a white tagfoundation seed is produced from Breeder seed by a Foundation seed organization Registered seed -- A purple tag is used to identify the registered seed class This is the second generation from Breeder seed Registered seed is sometimes eliminated under the limited generation system Certified seed -- The certified seed that is used as planting stock for general crop production is marked with a blue tag The following procedures are often employed when a seed crop is certified: Application -- An application must be filed by a predetennined date in order for the crop to be eligible Only eligible cultivars from an approved list are considered The source of the seed used for planting stock must be verified Field history must be established The isolation distances must be met The crop must be inspected at the seedling stage The seed crop is inspected prior to harvest Seed is cleaned at an approved warehouse Seed is sampled by the certifying agency Then it is tested by the state seed lab for purity, gennination, and noxious weeds Seed is tagged by the certifying agency During the production of Foundation seed, the combine is also inspected, so this is an additional step in the production of a seed crop under the certified system 17 References Elgersma, A and AJP Van Wijk 1997 Breeding for higher seed yields in grasses and forage legumes In DT Fairey and JG Hampton (ed) Forage Seed Production 1: Temperate Species, p CAB International, Wallingford UK Rackharn, R L 2002 History of specialty seed crop production in the Pacific Northwest Willamette Valley Specialty Seed Crops Assn, pp 133 McDonald, MB, and WD Pardee 1985 The role of seed certification in the seed industry CSSA Spec Publication Number pp McDonald, MB, and L Copeland 1997 Seed production: principles and practices Chapman and Hall, New York Meyer, WA, and cr Funk 1989 Progress and benefits to humanity from breeding cool-season grasses for turf In DA Sleper, KH Asay, and JF Pedersen (ed) Contributions from Breeding Forage and Turf Grasses CSSA Spec Pub! 15:31-48

11 Young, We III, and RE Barker 1997 Ryegrass seed production in Oregon In FM Roquette, Jr and LR Nelson (ed) Ecology, Production, and Management of Lo/ium for Forage in the USA CSSA Spec Publ 24: Youngberg, H 1980 Techniques of seed production in Oregon In P D Hebb1ethwaite (ed) Seed Production Butterworths, London 11