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Showing papers on "Plant disease resistance published in 1977"


Journal ArticleDOI
TL;DR: The data reported so far support the idea that model II rather than model I is the realistic one, which revealed that populations with a polygenic resistance based on the gene-for-gene action have an increased level of resistance compared with the addition model, while its stability as far as mutability of the pathogen is concerned is higher compared to those with an additive gene action.
Abstract: Horizontal, uniform, race-non-specific or stable resistance can be discerned according to Van der Plank, from vertical, differential, race-specific or unstable resistance by a test in which a number of host genotypes (cultivars or clones) are tested against a number of pathogen genetypes traces of isolatest If the total non-environmental variance in levels of resistance is due to main effects only differences between cultivars and differences between isolates) the resistance and the pathogen many (in the broad sense) are horizontal in nature Vertical resistance and pathogenicity are characterized by the interaction between host and pathogen showing up as a variance compenent in this test due to interaction between cultivars and isolates A host and pathogen model was made in which resistance and pathogenicity are governed by live polygenic loci Within the host the resistance genes show additivity Two models were investigated in model I resistance and pathogenicity genes operate in an additive way as envisaged by Van der Plank in his horizontal resistance Model II is characterized by a gene-for-gene action between the polygenes of the host and those of the pathogen The cultivar isolate test in model I showed only main effect variance Surprisingly, the variance in model II was also largely due to main effects The contribution of the interaction to the variance uppeared so small, that it would be difficult to discern it from a normal error variance So-called horizontal resistance can therefore be explained by a polygenic resistance, where the individual genes are vertical and operating on a gene-for-gene basis with virulence genes in the pathogen The data reported so far support the idea that model II rather than model I is the realistic one The two models also revealed that populations with a polygenic resistance based on the gene-for-gene action have an increased level of resistance compared with the addition model, while its stability as far as mutability of the pathogen is concerned, is higher compared to those with an additive gene action Mathematical studies of Mode too support the gene-for-gene concept The operation of all resistance and virulence genes in a natural population is therefore seen as one integrated system All genes for true resistance in the host population, whether they are major or minor genes are considered to interact in a gene-for-gene way with virulence genes either major or minor, in the pathogen population The models revealed other important aspects Populations with a polygenic resistance based on a gene-for-gene action have an increased level of resistance compared to populations following the addition model The stability, as far as mutability of the pathogen is concerned, is higher in the interaction model than in the addition model The effect of a resistance gene on the level of resistance of the population consists of its effect on a single plant times its gene frequency in the population Due to the adaptive forces in both the host and the pathogen population and the gene-for-gene nature of the gene action an equilibrium develops that allows all resistance genes to remain effective although their corresponding virulence genes are present The frequencies of the resistance and virulence genes are such that the effective frequencies of resistance genes tend to be negatively related to the magnitude of the gene effect This explains why major genes often occur at low frequencies, while minor genes appear to be frequent It is in this way that the host and the pathogen, both as extremely variable and vigorous populations, can co-exist Horizontal and vertical resistance as meant by Van der Plank therefore do not represent different kinds of resistances, they represent merely polygenic and oligogenic resistances resp In both situations the individual host genes interact specifically with virulence genes in the pathogen Van der Plank's test for horizontal resistance appears to be a simple and sound way to test for polygenic inheritance of resistance The practical considerations have been discussed The agro-ecosystems should be made as diverse as possible Multilines, polygenic resistance, tolerance, gene deployment and other measures should be employed, if possible in combination

251 citations


Book
01 Jan 1977
TL;DR: Part I: Plant Disease: The Diseased Plant The Microbial Pathogens Pathogen Structure And Function Disease Assessment And Forecasting Plant Disease Epidemics Part II: Host-Pathogen Interactions: Entry And Colonization Of The Host The Physiology Of Plant Disease Microbial pathogenicity Plant Defence Host-pathogen Specificity Part III: Disease management: Disease Management by Chemicals Disease Management By Host Resistance Biological Control of Plant Disease An Integrated Approach To Disease Management
Abstract: Part I: Plant Disease: The Diseased Plant The Microbial Pathogens Pathogen Structure And Function Disease Assessment And Forecasting Plant Disease Epidemics Part II: Host-Pathogen Interactions: Entry And Colonization Of The Host The Physiology Of Plant Disease Microbial Pathogenicity Plant Defence Host-Pathogen Specificity Part III: Disease Management: Disease Management By Chemicals Disease Management By Host Resistance Biological Control Of Plant Disease An Integrated Approach To Disease Management

184 citations


Journal ArticleDOI
TL;DR: The genetics of seedling resistance to leaf rust was investigated in what (Triticum aestivum L.) introductions PI 268454, PI 58548 and PI 268316, originally collected in Afghanistan, China and Iran, respectively.
Abstract: The genetics of seedling resistance to leaf rust (Puccinia recondita Rob ex Desm) was investigated in what (Triticum aestivum L) introductions PI 268454, PI 58548 and PI 268316, originally collected in Afghanistan, China and Iran, respectively PI 268454 was heterogeneous for resistance A selection (PI 268454a) has a gene that confers a 1+ reaction while a second selection (PI 268454b) probably has resistance gene Lr2b PI 58548 has two genes for resistance, one giving a 1+ reaction and the second a 2+ These two genes interact to produce a; 1 reaction PI 268316 has three interacting genes, one giving a 1+ reaction, the second a 2+ and a third resistance gene similar to LrB The gene giving the 1+ reaction was common to all three introductions PI 58548 and PI 268316 carry different genes for infection type 2+ Backcross lines of the single genes were produced Implications to breeding for disease resistance of genes interacting to produce different phenotype are discussed

103 citations


Journal ArticleDOI
TL;DR: Reduced genetic variability, improved cultural practices, and continuous cropping with rice, intended for increased rice production, have increased the genetic vulnerability of the crop.
Abstract: Rice is the host for more disease and insect organisms than any other cereal crop. More than 60 diseases and over 100 insect species are known to attack the rice crop. Some of these are of major international importance. During the last 10 years major changes have occurred in the varietal composition and cultural practices for rice. High yielding varieties are now planted on approximately 25% of the 130 million hectares planted to rice all over the world. These varieties are characterized by early maturity, photoperiod insensitivity, short stature, high tillering, and dark green erect leaves. Approximately 80 improved plant type varieties have replaced literally hundreds of tall traditional cultivars, thereby reducing the genetic variability of the crop. In the wake of introduction of varieties with improved plant type, farmers have started to use improved cultural practices such as more fertilizer and higher plant populations per unit area. Development of irrigation facilities and availability of early maturing, photoperiod-insensitive varieties have enabled the farmers in tropical Asia to grow successive crops of rice throughout the year on large areas. Reduced genetic variability, improved cultural practices, and continuous cropping with rice, intended for increased rice production, have increased the genetic vulnerability of the crop. Within the last few years serious outbreaks of diseases and insects on rice have occurred in several countries. Very little research has been done on the chemical control of rice diseases in the tropics. Several insecticides have been identified, but chemical control of high insect populations for prolonged periods in tropical climates where insect generations overlap throughout the year is very expensive. Social and economic conditions in the tropics present other obstacles to the chemical control of rice diseases and insects. The use of host resistance to control diseases and insects is the most logical approach to overcome these production constraints.

66 citations



Journal ArticleDOI
TL;DR: Host-parasite interactions that lead to susceptibility or resistance of a host plant to a pathogen are likely to take place at a very early stage--during transcrip­ tion and translation.
Abstract: The development of obligate fungal parasites on their host plants is controlled by genes for resistance in the host and genes for virulence in the pathogen (30). Analyses by techniques of classical genetics have led to the concept of the gene-for­ gene relationship (25, 30, 52), which accounts for the striking degree of varietal specificity exhibited by the physiological races of phytopathogenic fungi such as the rusts and powdery mildews. While this concept has been useful in investigations concerning the nature of disease resistance in terms of Mendelian genetics (31, 52), the molecular basis of the action of specific resistance genes in determining the outcome of host parasite interactions is far from clear. Infection of higher plants by fungal pathogens is accompanied by major changes in the metabolism of the host. These metabolic transitions have often been correlated with the appearance of new isozymes or enzymes with altered properties (66, 69). Therefore, host-parasite interactions that lead to susceptibility or resistance of a host plant to a pathogen are likely to take place at a very early stage--during transcrip­ tion and translation. During the last five years, remarkable progress has been achieved toward under­ standing the mechanism of eucaryotic gene expression. The transcription of DNA into RNA in plants, animals, and fungi is controlled by two mechanisms: (a) template activity of chromatin as determined by the structure and arrangement of chromosomal proteins (33, 76) and (b) the transcriptive specificity of the multiple molecular forms of RNA polymerase (5, 27). Furthermore, gene expression is now known to be regulated during both transcriptional and post-transcriptional process­ ing (5, 9, 22) of all classes of precursor RNA into biologically active ribosomal RNA

14 citations


Journal ArticleDOI
TL;DR: Results from these experiments support the contention that all plants have efficient mechanisms for disease resistance though resistance may be latent in the presence of some pathogens under certain conditions and suggest a new approach to breeding for Disease resistance in plants.
Abstract: The interactions, green bean-Colletotrichum lindemuthianum and cucurbits-Colletotrichum lagenarium, have been used in our laboratory to study the presence and activation of latent mechanisms for disease resistance in plants. Green bean hypocotyls inoculated with cultivar-non-pathogenic races of C. lindemuthianum, the heat-attenuated fungus, or some non-pathogens of green bean were locally and systemically protected from disease caused by subsequent inoculations with cultivar-pathogenic races of the fungus. Cultivars of bean susceptible to all known races of the pathogen were protected against the pathogen by prior inoculation with some non-pathogens. Recently we observed that inoculation of a cotyledon or first true leaf of cucumber, watermelon or muskmelon with Colletotrichum lagenarium systemically protected plants against the pathogen. Protection was evident as a reduction in the number and size of lesions. Inoculation of the first true leaf, when the second true leaf was partially expanded, systemically protected cucumber plants for 4–5 weeks. Plants at this time had 8–12 leaves. A second or booster inoculation 3 weeks after the first inoculation extended protection, and protection was effective with resistant and susceptible cucumber cultivars. A direct relationship existed between the number of spores used for protection and the extent and duration of protection. A single lesion elicited significant protection. Inoculated leaf one was not necessary to maintain protection of leaf two or to initiate and maintain protection in developing leaves once protection was initiated in leaf two. Inoculation of leaf one with the pathogen protected cucumber and watermelon plants in the field against the pathogen. Results from our experiments support the contention that all plants have efficient mechanisms for disease resistance though resistance may be latent in the presence of some pathogens under certain conditions. Activation of mechanisms for resistance may provide a practical means for disease control by plant immunization and suggests a new approach to breeding for disease resistance in plants.

13 citations






Journal Article
TL;DR: Three clones of pond pine, a species intermediate in resistance to fusiform rust, were evaluated for rust resistance in a field test, and significant differences in rust infec­ tion and height growth were observed.
Abstract: Three clones of pond pine, a species intermediate in resistance to fusiform rust, were evaluated for rust resistance in a field test, Significant differences in rust infec­ tion and height growth were observed. Selection for both rust resistance and rapid early growth is feasible in this species. Plant Dis, Reptr, 61: 916-918. Additional key words: southern pines, disease resistance. Fusiform rust of southern pines, caused by Cronartium fusiforme Hedge. & Hunt ex Cumm., is the most serious forest tree disease in the South. Damage caused by this disease on slash (Pinus elliottii var, elliottii) and loblolly (P. taeda) pine alone is conservatively estimated at $28 million annually (3). Pathologists and foresters have been aware of the differences in the resistance of different species of southern pines to infection by the rust fungus (2 ). In some areas of high rust hazard, the choice of species for planting may be dictated by this disease. Highly susceptible slash pine has been discriminated against in favor of more tolerant loblolly pine. Pond pine (P. serotina), which is intermediate in resistance, has been considered as an alternative speciesin areas where even loblolly is seriously damaged by rust. In addition to variation among species, wide differences in rust susceptibility among selec­ tions within a pine species have been demonstrated. In particular, certain open-pollinated families derived from specific clones of slash and loblolly pines are recognized for their resist­ ance to infection which far exceeds that of standard nursery stock (1, 4). This study was designed to evaluate the relative levels of resistance to infection by C. fusiforme in three clones of P. seroti.na. Pond pine might have potential for use on sites where it would grow well. MATERIALS AND METHODS The seedlings used in this study were members of half-sib families from three clones in seed orchards of the Westvaco Corporation, Summerville, S. C. Clones selected were from the North Carolina State University Industry Cooperative tree improvement program. They had demonstrated superior growth and yield characteristics, as well as freedom from infection by fusiform rust. The seedlings were grown in nursery beds at Athens, Georgia, and planted in February, 1970 at the Santee Experimental Forest near Charleston, S. C. Each half-sib family was planted in plots containing 72 seedlings (8 rows of 9 seedlings each) at a 8 x 8-foot spacing, in a randomized block design with four blocks. In each 72-tree plot only the center 20 trees (0. 0294 acres) were used as a measurement plot. Appropriate analysis of variance was carried out with the following variables: survival, total height, and stem, branch and total infections by the fusiform rust fungus at 2, 3, and 6 years after planting. Two height variables were analyzed: average height of all trees and average height of the four tallest trees on the 20-tree measure­ ment plots (equivalent to th.e tallest 136 trees per acre). The latter may be a more sensitive measurement because trees of lower vigor which might not survive are not included.