Conclusions Several features of agricultural biotechnology have been discussed in this section. Brown the topic and the symposium. Such advocacy will be dependent on the specialized knowledge of plant pathologists, breeders and agronomists being presented into the arena of international conventions and politics. This is expected to provoke other agricultural exporting countries into similar action because of the advantage which low pesticide users can command in trade. They studied changes in race frequencies in pure stands and in four layouts of mixture. A second factor which is predicted to favour complex pathogen races is a high rate of allodeposition, so that there is a relatively high probability of spores, formed on one variety, infecting another Barrett, 1978, 1980; Ostergaard, 1983.
Agroecology recognizes the importance of ecological theory in agriculture, but explicitly acknowledges agriculture as a human activity, carried out within ecosystems in which human social systems are an integral part Altieri, 1987. Theoretical and Applied Genetics 74, 87-94. This volume focuses on issues of plant pathology and sustainability, such as short term economic plans versus long term economic visions in farming and forestry. Multilines and super-races - a reply. The present, highly successful Australian cotton industry is some 25 years old. Such social, institutional and political aspects of high productivity agricultural systems are as significant to the successful introduction of alternative strategies of plant protection as the scientific problems posed by them.
Authors are alternately optimistic and pessimistic about the prospects that biocontrol will ever provide much economic control of plant pathogens Adams, 1990; Andrews, 1992; Sutton and Peng, 1993. It is essential that researchers and practitioners respect the differences in agriculture as practiced in different parts of the world. Keywords: Pathology, Plant, postharvest, latest, important, pages, fruit, edition, Century, Publisher, Springer, 1402089295, approaches, development, toxicity, alternative, means, disease, effective, reduce. The dynamics of genes in populations. Recombination and selection in populations of plant pathogens. In many pathogens, including those that cause rusts, smuts and powdery and downy mildews, many virulences conform to the gene-for-gene hypothesis of Flor 1956.
If these two factors did indeed reduce the population size of the pathogen, they would also have reduced the number of virulent mutants that might have started an epidemic of stem rust on barley. Despite the fact that the gene mlo, for resistance to barley mildew, has been used in popular spring barley varieties for 15 years J rgensen, 1992 , no commercial winter barley variety has yet been bred with mlo perhaps because of the difficulty of breeding successful varieties from crosses of winter and spring cultivars. On the Nature and Genetic Basis for Resistance and Tolerance to Fungal Wilt Diseases of Plants. Work on cereal pathology at the John Innes Centre is supported by the Ministry of Agriculture, Fisheries and Food. Combinations of resistance genes have provided good resistance to wheat stem rust in Australia for many years Mclntosh, 1992. The natural toxins in different strains of Bt are selective amino acids which bind to receptor proteins in insect gut, causing the gut wall to disintegrate; over 50 compounds have been identified, often with very selective targets. Sweden, Denmark and the Netherlands have now embarked on such programmes of agricultural chemical reduction Hurst, 1992.
Nelson for the suggestion to pursue the topic. This volume focuses on issues of plant pathology and sustainability, such as short term economic plans versus long term economic visions in farming and forestry. Defense Responses of Plants to Pathogens. There, wheat was free of this serious disease until 1979, when the first outbreaks were caused by race 104E137A-. Lettuce downy mildew: a case study in integrated control. It has expanded rapidly to a position of being the The Concept of Agricultural Sustainability 11 fourth largest trader of cotton internationally earning more in exports than the total export value of fisheries and rivalling forest products, and is characterized by a sophisticated and well-informed producer population.
The evolution of such super-races, and their importance relative to simpler races, is favoured in theoretical models if there is little or no selection against unnecessary virulence Groth, 1976; Barrett and Wolfe, 1978; Marshall and Pryor, 1978. However, we can distinguish two different processes by which a virulence may be selected. A large body of literature on traditional farming systems is already accessible, but most of it is not in the agricultural science literature. The high cost of mildew infection therefore means that growers are receptive to workable schemes for controlling it Crute, 1989. A no-tillage tomato production system using hairy vetch and subterranean clover mulches. With a high rate of allodeposition, however, complex races would predominate and ultimately become fixed. As with the introduction of a new cuhivar in the cycle's first phase, many factors other than susceptibility to one single disease contribute to the withdrawal of a variety from cultivation.
It does not ask the far more important question for environmental and economic sustainability, namely, 'Will it fit into an agroecosystem or into an economic system, over the long term'. Alternative strategies being investigated currently are the growing of buffer alternative host crops around each block of cotton, the use of Bacillus thuringiensis Bt mixed with, or instead of, pyrethroids, suppression of the resistance mechanism via oxidative detoxification with piperonyl butoxide, and the projected development of genetically engineered host-plant resistance Forrester, 1990. Durability and Genetics The second reason for durability is shown by another barley disease resistance gene, mlo. It is no doubt as foolish to expect traditional practices to transfer wholesale to industrialized countries as vice versa. For instance, race 56 caused severe rust on the bread wheat variety Ceres in 1934 and 1937, while race 15B devastated durum wheat in 1953 and 1954 Stakman, 1955. This case illustrates how multiple dominant antagonist traits can be understood and combined with appropriate application methods to generate a disease-management strategy that is apparently ecologically sound ,Jones and Kerr, 1989.
Sustainability is an economic state where the demands placed upon the environment by people and commerce can be met without reducing the capacity of the environment to provide for future generations. Pathogen response to host resistance and its implication in breeding programmes. In North America, combinations of resistance genes which have included Sr2 have provided durable resistance to stem rust, while gene combinations including Lrl3 or Lr34 have been durably effective in controlling leaf rust Puccinia recondita f. Such discussion has largely been within the ambit of non-government environmentalist organizations, and vary from the frankly emotive anti-science stand to the informed and thoughtful prospect of replacing one flawed system with another. If it were not, we would expect to have seen local, virulent populations, which were genetically different from one another. . On the Nature and Genetic Basis for Resistance and Tolerance to Fungal Wilt Diseases of Plants.
Subsequent spread of new pathotypes occurred at the rate of one to two a year, resulting from a single mutational event in each generation, in a step-wise progression. The old, defeated resistance may th,:refore be combined with effective resistances in new varieties. Isolating appropriate genes and establishing stable transgenically derived resistance that is durable in the field requires lengthy experimentation. The effective population size of a subpopulation of E. The translocated chromosome, designated 1B-1R, carries the gene Yr9 for resistance to yellow rust Macer, 1975.
In 'The Cereal Rusts, Vol. For some 20 years the theoretical treatment of ecology has been stimulated by the insights of Robert MacArthur and his associates into relationships between the abundance and diversity of species and their environments. Focusing biological control research through a lens of applied ecology predisposes biological control approaches to environmental sustainability. Annales d'Amilioration des Plantes 28, 479-491. Johnson 1984 has emphasized that durability is only a description about the past behaviour of a resistance. It must be noted, however, that scientific risk assessment addresses only one small component of environmental sustainability.