The past half century has been a most astounding time for those of us fortunate enough to have been involved in research and teaching about tall fescue. The whole approach of first determining the cause of tall fescue toxicosis and then uncovering the intricate series of biochemical and physiological processes and interactions among animals, plants, and fungi has been most fascinating. Eventually, practical solutions were developed, even though some promising avenues turned out to be blind alleys. The whole 35-year process has seemed akin to a complicated detective novel, complete with some distracting issues and alleged but innocent perpetrators.
When ‘Kentucky 31' was first selected in 1931 and then released during World War II, there was no concept of the upheavals it would occasion in agricultural science. By the mid 1950s, tall fescue had filled a large ecological niche in the southern United States, and its use for forage and seed production had precipitated political polemics, enriched a few opportunists, and created a perplexing and sometimes deadly problem for cattle that ingested it. For another 25 years, the effects of tall fescue toxicosis were tolerated because of the wide adaptation of the grass and the characteristics that made it a valuable forage and soil cover, in spite of performance by cattle that was not satisfactory in some seasons, as compared with other forage plants.
It was not until the late 1970s that perspicacious and persistent investigators in Georgia and Alabama rediscovered the association between tall fescue and the Neotyphodium coenophialum fungal endophyte originally described by J.C. Neil in 1941 and published in the New Zealand Journal of Science and Technology (see Chapter 1). The scientists in Alabama and Georgia were able to link the endophyte-host grass combination to unsatisfactory cattle performance. Eventually, it was shown that removal of the fungus improved cattle performance but resulted in decreased plant persistence. It took an additional 35 years to unravel this extremely complicated toxicosis puzzle, with numerous discoveries in many fields of science, including the production of improved cultivars in novel ways and education programs permitting livestock producers to multiply their efficiency and productivity
A major advance in the management of fescue toxicosis occurred with discoveries of Neotyphodium strains that lacked the toxins deleterious to livestock but retained the benefits of plant persistence and growth. Such endophytes were inserted into improved cultivars and marketed for use in pastures. This research originated in New Zealand with their scientists' innovative work on perennial ryegrass, a fairly close relative of tall fescue. The future is very promising for advanced methods of selection and engineering of desirable endophytes, as well as designing of compatible associations with new tall fescue cultivars that persist and grow better in environments characterized by prolonged water deficit or pest predation. Such applications already are being applied to the growing use of "summer-dormant" types of tall fescue. The use of these new types may expand greatly as climate change exacerbates heat and drought occurrences.
The importance of tall fescue has stimulated additional studies of its taxonomic characterization. In addition to the traditional consideration of morphological characteristics, genetic criteria and interfertility relationships were used to trace the evolution of tall fescue, its numerous relatives, and the fungal symbionts through the ages. These new understandings led to new insights into processes of grass and fungal evolution and showed that interspecific hybridization can obscure species boundaries, but serves as a rapid means of combining distinct genomes into novel progeny with enhanced evolutionary potential.
The need to document the wide adaptation of tall fescue on the Earth, limited by extremes of temperature, water availability, and physical and chemical aspects of soils, led to an international effort to employ advanced spatial analyses to create quantitative, highly detailed, and accurate computer-generated species suitability maps based on biophysical characteristics of regions and plants. The resolution in such maps will improve as results of research on factors limiting tall fescue growth and survival become available. The development of these landscape-level suitability maps for tall fescue provides a model for future efforts with other species and regions as tolerance values and climate and soil spatial grids are refined and new tall fescue genotypes arise or are created.
Recognition of the effects of the fungal endophyte stimulated explorations of new ways to establish tall fescue stands in areas widely different in the climatic and soil conditions that affect survival, productivity, and use of fescue, especially when the preceding crop was a stand of fescue infested with the wild type of endophyte (wt) or common toxic endophyte (E+ = cte), or when fescue was new to the area. Since tall fescue has one of the longest growing seasons among cool-season grasses, management strategies that can further extend the grazing season were developed, especially those that tend to equalize yield distribution across seasons using complementary warm-season plants. Pending the development, availability, and deployment of novel nontoxic endophytes in elite cultivars, management schemes were designed that could alleviate the toxic effects of E+ tall fescue on cattle, horses, and other herbivores.
Awareness of the involvement of the fungal endophyte in affecting interactions among tall fescue host plants and disease organisms, insect vectors and pests, some nematodes, and climatic and edaphic conditions stimulated many scientists in several countries to investigate these relationships and develop procedures for improving forage persistence, quality, and growth. The seemingly symptomless but delicately balanced partnerships between grasses and endophytic fungi stimulated innovative electron microscopic studies of the location and structure of the intercellular hyphae in fescue tissues and led to the discovery of the intercalary growth of hyphae, explaining how these hyphae can extend as fast as leaves are growing.
Knowledge of the complicated sequences of biochemical reactions in the plant that occur when some strains of N. coenophialum are present had to be understood before the mechanisms could be quantified or modified. These studies of alkaloids, the compounds that are toxic to herbivores but also help protect the plant from stresses and pests, involved scientists at several laboratories working over many years across national boundaries. Some compounds still remain to be identified and their reactions clarified. Nonetheless, practical recommendations for measuring endophytes in tall fescue pastures have been developed and publicized.
Much information has been accumulated about the effects of numerous environmental and management factors on the nutritive value of fescue at different stages of growth for domesticated consumers of tall fescue. It appears that the nutrient composition of the forage is little affected by the endophyte status, and that reduced animal performance instead is related to decreased nutrient intake and the effects of the alkaloids ingested. The nutritive value and quality of tall fescue forage can be evaluated now without the confounding influence of toxins from the fungal endophyte-grass symbiont. Great care must be exercised when considering data obtained prior to the recognition of the endophyte.
Signs of tall fescue toxicosis in cattle and sheep include decreased milk production, birth weight, pregnancy rate and serum prolactin levels, and increased respiration rate. Mares are more sensitive to the toxic alkaloids than cattle, and mares have increased gestation lengths, birthing difficulties accompanied by increased foal and mare mortality, stillborn foals, and poor milk production when consuming E+ fescue. Valuable mares and foals exposed to E+ tall fescue can be saved with oral administration of domperidome. Unfortunately, this pharmaceutical product is too expensive for routine use with herbivores. The physiological basis for tall fescue toxicosis in ungulates, as affected by environmental conditions, has been studied extensively. Many of the mechanisms involved have been elucidated, promising not only eventual relief from their effects in animals, but also portending answers to human medical questions, such as those involving flexibility and diseases of blood vessels.
A large range in genetic variability for many important traits exists in tall fescue, facilitating modification of the species. Persistence and stress tolerance are traits often targeted for improvement in both forage and turf types. Tall fescue breeding is poised to enter a new era as biomolecular technologies are being used to develop improved genotypes of grass hosts and fungal endophytes. Genomics provides insight into the genetic basis for traits of interest, whereas molecular DNA markers can be used for genetic improvements. Several molecular marker systems have been developed to provide understanding of the genetic basis for traits of interest and to construct genetic linkage maps. Genetic transformation is being used within improvement programs, and methods for generating transgenic tall fescue plants have been developed.
Most U.S. seed production for improved cultivars of forage and turf tall fescues is done in the Pacific Northwest. Some serious diseases can affect seed production, but most can be contained when control recommendations, developed over time, are followed. The existence of fungal endophytes has complicated seed production because improved turf cultivars must be high in endophyte content, whereas forage cultivars must be free of the fungus or preferably contain novel nontoxic strains. Maintaining viability of desired endophytes as well as high seed germination and purity demands careful control and monitoring of all seed and environmental conditions, from establishment and production through harvest, storage, and marketing of both public and private cultivars. Seed laws and regulations, promulgated for consumer and breeder protection, need enforcement and may need amending to take into consideration these new developments.
Environmental considerations have led to the prohibition of burning the straw remaining after seed harvest. When toxic E+ straw is fed to cattle, many problems can arise. Careful analytical procedures have been developed and are being refined to monitor fescue forage, seed, and straw endophyte and alkaloid contents so cattle can be protected and valuable markets preserved.
In temperate regions of the developed world, tall fescue is used extensively for residential, industrial, athletic, and soil protection turfs. Residential turfgrass contributes to quality of life, while industrial turf beautifies areas surrounding commercial and manufacturing establishments. Tall fescue is used extensively for playgrounds, playing fields of all kinds, and golf fairways and other areas. Turf cultivars high in fungal endophyte content, specifically developed for tolerance to close clipping and intensive management, have been developed in public and private breeding programs since the 1980s. However, where tall fescue has overtaken nonagricultural areas, its dense canopy and endophyte-toxin content have diminished the diversity of habitat structure and food quality for sustaining populations of insects, birds, and mammals. Wildlife restoration efforts often are challenged with eradicating old fescue stands and introducing diverse, native plant communities.
The future of tall fescue is linked with the future of an environmentally conscious, energy-efficient, productive animal agriculture that uses land that should not be in row crops for the rearing of domestic and other animals. Tall fescue will also play an increasing role in protecting soil and water and enhancing the aesthetics of urban and agricultural landscapes. As the world population expands and the availability of arable soils decreases, limited edaphic resources will have to be used more sustainably, while providing nutritional sustenance for all humanity. Tall fescue will continue to be a desirable agricultural grass species, in most humid and temperate regions, for capturing solar energy transformed into human food via animals capable of digesting cellulose. Thus, domestic livestock will remain a viable part of agriculture where soils are too steep, too wet, too dry, too rocky, too shallow, too high in elevation, or too remote for cultivated crops.
One of the greatest innovations in the world was the development of the U.S. land-grant college concept. The original Morrill Act, passed by Congress and signed by President Lincoln on 2 July 1862, opened institutions of higher education to all members of society. The grant of western lands made possible the flowering of the idea. In March 1887, the Hatch Act instituted a public commitment to research directed to the needs of farmers, providing a permanent appropriation to each state each year for establishing and maintaining an agricultural experiment station. In 1914, the Smith-Lever Act gave shape and funding to extension. The land-grant colleges were the foundation on which modern agricultural productivity and efficiency were able to rise and flourish.
The tall fescue story described in this monograph constitutes a shining example of the kind of advances in agricultural science and their practical applications made possible by the land-grant colleges and the U.S. Department of Agriculture during the past century, augmented in more recent years by contributions from foundations and portions of the agribusiness community. Scientists and organizations in other countries, especially in New Zealand, also made outstanding contributions to solving complex and fascinating problems, such as those created by the fungal endophyte. Thus, relatively small investments in research have yielded many returns in forage productivity and utilization as the technology was extended to producers, helping them to improve their efficiency or facilitating the change from cash cropping to pastoral agriculture. Although several researchable questions remain to be solved, basic and applied approaches eventually will shed light on these problems. In the meantime, as current knowledge is disseminated and applied to enhance better and more sustainable management practices, tall fescue husbandry will play an increasing role in ensuring long-term food and feed sustainability in a fragile world with an increasing population, doing its share to protect soil and water resources while transforming solar energy into feed on lands that should not be tilled.