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1.
Summary 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. 相似文献
2.
Durability of resistance against fungal, bacterial and viral pathogens; present situation 总被引：8，自引：0，他引：8
Jan E. Parlevliet 《Euphytica》2002,124(2):147-156
In evolutionary sense no resistance lasts forever. The durability of a resistance can be seen as a quantitative trait; resistances
may range from not durable at all (ephemeral, or transient) to highly durable. Ephemeral resistance occurs against fungi and
bacteria with a narrow host range, specialists. It is characterised by a hypersensitive reaction (HR), major gene inheritance and many resistance genes, which often occur
in multiple allelic series and/or complex loci. These resistance genes (alleles) interact in a gene-for-gene way with a virulence
genes (alleles) in the pathogen to give an incompatible reaction. The pathogen neutralises the effect of the resistance gene
by a loss mutation in the corresponding avirulence allele. The incompatible reaction is not elicited any more and the pathogenicity
is restored. The pathogens can afford the loss of many avirulences without loss of fitness. Durable resistance against specialised
fungi and bacteria is often quantitative and based upon the additive effects of some to several genes, the resulting resistance
being of another nature than the hypersensitive reaction. This quantitative resistance is present to nearly all pathogens
at low to fair levels in most commercial cultivars. Durable resistance of a monogenic nature occurs too and is usually of
a non-HR type. Resistance against fungi and bacteria with a wide host range, generalists, is usually quantitative and durable. Resistances against viruses are often fairly durable, even if these are based on monogenic,
race-specific, HR resistances. The level of specialisation does not seem to be associated with the durability of resistance.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Field, pots and mini-rhizotrons experiments revealed the existence of useful levels of avoidance and resistance to Orobanche crenata Forsk. within Lathyrus cicera L. accessions, in addition to escape due to precocity or to reduced root biomass. This resistance was characterized by several
phenotypic mechanisms of defence which acted alone or in combination, including low stimulation of parasitic seed germination,
prevention of the radicle penetration inside the root and prevention of a correct connection by the parasite with the host
vascular tissue being visible by reduced development of established parasitic tubercles or abortion of the parasitic tubercles
formed. 相似文献
4.
Nine populations of rye (Secale cereale L.; the cultivars ‘Kustro’, ‘Danko’ and ‘Carokurz’. a breeding population PA 14/75 and five Iranian primitive ryes) were tested with three or two pathotypes of powder)’ mildew (Erysiphe graminis DC. f. sp. secalis Marchal) to determine the frequencies of vertical resistances. Similarly, three populations of powder)’ mildew isolated from the above eultivars were tested with two rye pathodemes to estimate the frequencies of vertical virulences. Tests were carried out on leaf segments cultivated in vitro. To explain the pattern of the host-parasite interaction, a model with at least four resistance and virulence genes was required. In the rye populations the genotypes of most plants could be determined unambiguously whereas in the powdery mildew populations no unique classification of one-postule isolates was possible due to the limited number of rye differentials. Both the host and the pathogen populations were polymorphic for resistance and virulence, respectively. In all lye populations except PA 14/75 the resistance frequencies were low. In the mildew populations the virulence frequencies were high and complex races occurred rather frequently. The virulence frequencies were related to the resistance frequencies of the respective host population. Results were compared with mathematical host-parasite models accounting for gene-for-gene interaction and balancing natural selection. Observations agree well with theory. 相似文献
5.
J. C. Zadoks 《Euphytica》1959,8(2):104-116
New physiologic races can be produced by mutation, hybridization or heterokaryosis. The genetics of the host parasite relationship can be explained on the basis of the gene-for-gene hypothesis of Flor. Resistance breeding is an important agent in the appearance of a new race and in the evolution of pathogenicity. In America the resistance breeding in wheat is conducted along the following lines:
- 1.Searching for sources of resistance by testing collections of varieties and hybrids. 相似文献
6.
Mitotic analysis of sticky chromosomes in aluminum tolerant and susceptible wheat lines grown in soils of differing aluminum saturation 总被引：3，自引：0，他引：3
Plant resistance is currently the most effective and environmentally safe method to control plant parasitic nematodes (PPNs).
Resistance genes generally act against sedentary PPNs by inducing a hypersensitive reaction that prevents the parasite installation
and/or reproduction. However, the recent emergence of virulent biotypes able to overcome the plant resistance genes may constitute
a severe limitation to this control strategy. In selection experiments conducted under controled environment, the genetic
variation, specificity and inheritance of nematode virulence have been demonstrated. Moreover, the occurrence of gene-for-gene
interactions has been shown in a few cases. Moleculars markers have been extensively used to investigate the genetic variability
of PPNs, but so far, the genomic polymorphisms observed are largely independent of virulence. Such data suggest that, within
a species, virulent isolates do not share a common origin, but are probably the result of independent mutational events. To
understand the molecular mechanisms responsible for virulence in PPNs, several strategies have been developed, in relation
with their mode of reproduction (parthenogenesis versus amphimixis). As an example, recent results obtained in our laboratory on the root-knot nematodes Meloidogyne spp. are presented. On a more general point of view, factors that may induce stable genome variability in PPNs, e.g. Transposition
of mobile elements and chromosomal rearrangements (leading to polyploidy, aneuploidy, etc) will also be considered. Advances in knowledge in these areas should have important consequences for the management and
durability of natural resistance genes, and for the engineering of new forms of resistance.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
Genes for Powdery Mildew Resistance in Cultivars of Spring Wheat 总被引：1，自引：0，他引：1
Twenty-three cultivars of spring wheat were inoculated with nineteen different powdery mildew isolates; their ruction patterns hive been compared with those of twenty-two cultivars/lines carrying identified powdery mildew resistance genes. Applying the gene-for-gene hypothesis, it is evident that three cultivars have none of the resistance genes used, seven others (including ‘Solo’) may carry Pm4b, only. The resistance pattern of ‘Selpek’ is identical to A/-1 resistant cultivars of winter wheat and may be explained by the presence of Pm5. The resistance pattern of Pm5 (Mt-i) cultivars is very different from a number of ‘Kolibri’-related cultivars of spring wheat. Since either all or nothing of that specific pattern has been transferred to all cross progenies of ‘Kolibri’, a single gene is assumed to oe responsible for it, preliminarily designated as Ml-k. The cultivar ‘Mephisto’ carries the ‘Normandie’ resistance (Pwl 2, 9). In five cultivars to spring wheat the combined effects of at least two of the above-mentioned sources have been found. Despite the fact that ‘Normandie’ and ‘Sappo’ are not closely related. ‘Sappo’ shows the complete ‘Normandie’ resistance pattern plus that of Pm4b. The same is true for ‘Planet’ and ‘Walter’. 相似文献
8.
R. S. S. Fraser 《Euphytica》1992,63(1-2):175-185
Summary Host resistance is the main means of control of plant virus diseases. This paper reviews the genetics of resistance and matching virulence. Theoretical models of basic compatibility between plant species and their viruses, and of resistance, are described and used to predict features of resistance genetics, and mechanisms. These predictions are compared with a survey of known examples of resistance.Resistance is mainly controlled at a single genetic locus, although more complex systems are known. About half of the resistance alleles studied were dominant, the remainder were either incompletely dominant or recessive. Doubt is cast on the reliability of assessing resistance genotypes (numbers of loci and dominace relationships) from distant phenotypic measurements such as symptom severity or plant growth. A model is proposed to reconcile apparent inconsistencies between genotype and phenotype.Dominant resistance alleles are strongly associated with virus localising mechanisms normally involving local lesions. Incompletely dominant and recessive alleles allow spread of the virus, but inhibit multiplication or symptom development. Fully recessive alleles may be associated with complete immunity.Most resistance genes in the survey had been overcome by virulent virus isolates with dominant localising resistance alleles especially vulnerable. Comparatively few resistance genes have proved exceptionally durable. Acquisition of virulence can be associated with loss of general pathogenic fitness, but in some cases this can be restored by further selection of the virus in resistant hosts.Virulence/avirulence determinants have been mapped to individual base changes in different functional regions of the viral genome. A virus may contain several virulence determinants and may develop a stable gene-for-gene relationship with a host having several resistance genes. It may be possible to design robust, oligogenic resistance systems which will be difficult for the virus to overcome. 相似文献
9.
Durability of resistance against potato cyst nematodes 总被引：1，自引：0，他引：1
Jaap Bakker 《Euphytica》2002,124(2):157-162
A requirement for evaluating the effectiveness of major resistance genes (R-genes) is detailed knowledge of the genetic variability
of the nematode populations in an area. Obtaining insight in the genetic variation in an area is a tour de force, because qualitative data are not sufficient allele frequency data at well studied loci are required. Another important step
in predicting the durability of major R-genes is to study the parasite at the molecular level. Also for nematodes it seems
that R-genes are part of a molecular surveillance system recognising foreign molecules. For potato cyst nematodes it is becoming
clear that numerous proteins are secreted to manipulate the host plant and it may be assumed that some of these secretory
proteins are also recognised by the host. Knowledge of the molecular nature and function of these avirulence gene products
may reveal clues to predict the durability of an R-gene. R-genes that recognise avirulence gene products that have a crucial
function in the nematode maybe very durable. When the current molecular models for gene-for-gene interactions are correct,
the durability of an R-gene may be predicted by studying the dispensability factor and functional constraints of the avirulence
gene products.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
11.
One hundred and twenty-seven spring barley varieties grown in Denmark since 1979 were characterized for resistance genes using 30 powdery mildew isolates. The resistance genes are traced in the pedigrees to verify the results. Eleven named genes, 12 tentatively named genes/resistances and six unknown resistances were found. Resistance in many varieties was based on combinations of either known genes or of known and new factors. The following five new or relatively new resistance genes more or less effective against the present powdery mildew populations were detected: the ‘Mlo’ resistance conferred by the recessive mlo gene with the characteristic infection type 0/(4), ‘Ricardo’ and ‘Turkish’ sources having gene Mla3 in common and ‘Turkish’ with Ml(Tu2) in addition. In three varieties the new resistance Ml(IM9) was found in combination with different Mia alleles. Variety ‘Jarek’ has two new unidentified resistances. 相似文献
12.
番茄叶霉菌无毒基因的研究进展 总被引：1，自引：0，他引：1
无毒基因是病原物遗传因子,其编码的产物激发病原物与植物特异性相互作用。病原物无毒基因与植物抗病基因产物间直接或间接相互作用导致产生的基因对基因抗性是植物抗病性的重要形式。番茄与叶霉病之间的特异互作被认为是遵循Flor的“基因对基因”假说的典型体系。绝大多数已克隆的无毒基因之间,及其与已知蛋白之间,均无显著的序列同源性。无毒基因具有双重功能：在含瓦补抗性基因植物中表现无毒效应,而在不含互补抗性基因植物中显示毒性效应。本文综述了番茄叶霉菌无毒基因的多样性、意义、结构及其功能等等,了解病原菌无毒基因的结构及功能,有助于了解病原物与植物的识别机制,对认识植物的抗病性,特别是非寄主植物对病原菌的广谱抗病性也具有重要意义。 相似文献
13.
E. C. Roumen 《Euphytica》1992,64(1-2):143-148
Summary Six rice genotypes, differing in partial resistance, were exposed to three isolates of the blast pathogen. Of the variance due to host and pathogen genotypes, 39% was due to host genotype effects, 60% was due to isolate effects, and only 1% was due to host genotype × isolate interactions. Although small, this interaction variance was highly significant and mainly due to the IR50 × W6-1 and IR37704 × JMB8401-1 combinations. Although behaving largely as race-non-specific (large main effects only), the partial resistance cannot be classified as race-non-specific. The results suggest that minor genes for partial resistance operate in a gene for gene relationship with minor genes in the pathogen. 相似文献
14.
R. E. Niks 《Euphytica》1988,37(1):89-99
Summary It is commonly argued that wild plant species with a very high level of resistance to a micro-organism which is pathogenic on a crop species would be useful donors of resistance. Whether this principle is true if the wild species is a distinct nonhost, remains to be proved. It is assumed that nonhost resistance, if not based on avoidance, rests on a poor adaptation of the micro-organism to general defence mechanisms in the plant. No basic compatibility is achieved. Major-genic hypersensitive host resistance would, according to the concept, be superimposed on basic compatibility. The defence reaction is switched on if a resistance allele recognizes a specific avirulence factor produced by the pathogen. The frequency of the resistance allele would depend on the selection pressure exerted by the pathogen population.In contrast to these concepts, there is evidence that nonhost resistance, at least to formae speciales, rests on an extremely high allele frequency of effective major genes for resistance, rather than on a complex of genes that play part in a general defence system. Especially the high allele frequency and the durability of the nonhost resistance are in conflict to what would be expected if the concepts hold true. It is concluded that part of the theoretical concepts needs to be revised or extended to reconcile them with the evidence. A major-genic base for nonhost resistance would be very interesting from the breeder's point of view, because transfer of such a resistance to a crop would be less hard to accomplish than that of more complex inherited defence systems. 相似文献
15.
Discovery,characterization and exploitation of Mlo powdery mildew resistance in barley 总被引：14，自引：0，他引：14
I. Helms Jørgensen 《Euphytica》1992,63(1-2):141-152
Summary Mlo resistance to barley powdery mildew is a relatively new kind of resistance. It was originally described in a powdery mildew resistant barley mutant in 1942 and has been mutagen-induced repeatedly since then. About 1970 it was also recognized in barley landraces collected in Ethiopia in the 1930s. It is unique in that 1) Mlo resistance does not conform to the gene-for-gene system; 2)mlo genes originating from different mutational events map as non-complementing recessive alleles in one locus; 3) all alleles confer the same phenotype, though with small quantitative differences; 4) it is effective against all isolates of the pathogen; and 5) the resistance is caused by rapid formation of large cell wall appositions at the encounter sites preventing penetration by the fungus. Powdery mildew isolates with elevated Mlo aggressiveness have been produced on barley in the laboratory, but have not been found in nature. Mlo resistance is considered very durable. The exploitation of Mlo resistance has been hampered by pleiotropic effects of themlo genes, vix. necrotic leaf spotting and reduced grain yield, but they have been overcome by recent breeding work. During the 1980s Mlo-resistant spring barley varieties have become cultivated extensively in several European countries, in 1990 on about 700,000 ha. 相似文献
16.
Past,present and future opportunities in breeding for disease resistance,with examples from wheat 总被引：6，自引：0，他引：6
Roy Johnson 《Euphytica》1992,63(1-2):3-22
Summary This introductory chapter contains some general comments about plant breeding and breeding for disease resistance. The use of disease resistant crop plants is an environmentally favourable method of controlling disease but the process of breeding for disease resistance is subject to several constraints. Among them is the variability of pathogens in relation to host resistance. Some parts of this variation can be resolved into gene-for-gene interactions, but the boundaries within which such interactions can be detected are not sharp. The discussion of this variation is illustrated by reference to some important diseases of wheat, especially yellow rust, septoria and eyespot. The objective of obtaining durable resistance is discussed and some contributions of new genetical and molecular techniques to breeding for resistance are considered. It is suggested that new technology will enhance breeding for disease resistance but that established techniques of plant breeding will remain relevant and important. 相似文献
17.
Orobanche crenata , Orobanche aegyptiaca and Orobanche foetida constitute serious threats to grain legumes in the Mediterranean Basin. Lentil can be severely infected by O. crenata . It can also be damaged although with less virulence by O. aegyptiaca , and can only be slightly infected by O. foetida . Resistance breeding is hampered by scarcity of proper sources of resistance in cultivated lentil and of a reliable and practical screening procedure. A germplasm collection of 23 wild Lens spp. accessions was screened for resistance to O. crenata under field conditions. A wide range of responses was observed, from complete resistance to susceptibility. The higher levels of resistance were observed in accessions of Lens ervoides , Lens odemensis and Lens orientalis . Resistance of selected accessions proved to be mainly because of early hampered tubercle formation, with no observed necrosis of established tubercles. No differences were observed in levels of induction of broomrape germination, but necrosis of broomrape radicles was significant in some cases, particularly in the L. odemensis–O. foetida interaction. Escape because of the reduced root biomass diminishing the chance of contact between host and parasite was also observed in L. odemensis . 相似文献
18.
Summary
Striga species are parasitic angiosperms that attack many crops grown by subsistence farmers in sub-Saharan Africa and India. Control of the parasite is difficult and genetically resistant crops are the most feasible and appropriate solution. In cowpea, complete resistance toStriga gesnerioides has been identified. Breeding for resistance in sorghum has identified varieties with good resistance toS. asiatica in Africa and India. One variety was also resistant toS. hermonthica in W. Africa. No such resistance toStriga has been found in maize or millets.Resistant varieties have usually been sought by screening germplasm in fields naturally infested withStriga. However, laboratory techniques have also been developed, including anin vitro growth system used to screen cowpeas for resistance toS. gesnerioides. Two new sources of resistance in cowpea have been identified using the system. The technique has also been used to investigate the mechanisms of resistance in this crop. Two mechanisms have been characterised, both were expressed after penetration of cowpea roots by the parasite.The resistance of some sorghum varieties toStriga is controlled by recessive genes. In cowpea, resistance toStriga is controlled by single dominant genes. The genes for resistance are currently being transferred to cowpea varieties which are high yielding or adapted to local agronomic conditions. OneStriga resistant cowpea variety, Suvita-2, is already being grown widely by farmers in Mali. Reports of breakdown of resistance in cowpea toStriga have not yet been confirmed, but a wider genetic base to the resistance is essential to ensure durability ofStriga resistance.Abbreviations ICRISAT
International Crops Research Institute for the Semi-Arid Tropics
- IITA
International Institute of Tropical Agriculture
- LARS
Long Ashton Research Station
- SAFGRAD
Semi-Arid Food Grain Research and Development 相似文献
19.
Parasitic angiosperms cause great losses in many important crops under different climatic conditions and soil types. The most widespread and important parasitic angiosperms belong to the genera Orobanche, Striga, and Cuscuta. The most important economical hosts belong to the Poaceae, Asteraceae, Solanaceae, Cucurbitaceae, and Fabaceae. Although some resistant cultivars have been identified in several crops, great gaps exist in our knowledge of the parasites and the genetic basis of the resistance, as well as the availability of in vitro screening techniques. Screening techniques are based on reactions of the host root or foliage. In vitro or greenhouse screening methods based on the reaction of root and/or foliar tissues are usually superior to field screenings and can be used with many species. To utilize them in plant breeding, it is necessary to demonstrate a strong correlation between in vitro and field data. The correlation should be calculated for every environment in which selection is practiced. Using biochemical analysis as a screening technique has had limited success. The reason seems to be the complex host-parasite interactions which lead to germination, rhizotropism, infection, and growth of the parasite. Germination results from chemicals produced by the host. Resistance is only available in a small group of crops. Resistance has been found in cultivated, primitive and wild forms, depending on the specific host-parasite system. An additional problem is the existence of pathotypes in the parasites. Inheritance of host resistance is usually polygenic and its transfer is slow and tedious. Molecular techniques have yet to be used to locate resistance to parasitic angiosperms. While intensifying the search for genes that control resistance to specific parasitic angiosperms, the best strategy to screen for resistance is to improve the already existing in vitro or greenhouse screening techniques. 相似文献
20.
Striga hermonthica (Del.) Benth., a parasitic weed of grasses, causes major yield reductions in the principal cereal crops of semi-arid Africa. Cultivar resistance is the most economic control measure, since adapted, resistant cultivars can be grown without additional input from the subsistence farmer. Information on the genetics of resistance to S. hermonthica is scant. This is partially attributable to the rarity of germplasms which exhibit stable resistance across geographical regions. The objective of this study was to determine if the stable resistance observed in sorghum [Sorghum bicolor (L.) Moench] cultivar SRN39 is heritable. Crosses were made between SRN39 and a susceptible parent, P954063. Parental, F1, F2 and backcross generations were grown in infested pots and development of both host and parasite was monitored. Significant variation among genotypes was observed for both host traits and effects on parasite populations. The F1 did not differ significantly in Striga resistance from the susceptible parent, suggesting recessive inheritance. However, hybrid vigor was exhibited by the F1 which yielded and developed as well as the resistant parent. Broad sense heritability ranged from 0.23 to 0.55 for host traits and from 0.10 to 0.43 for effect of genotypes on the Striga population. Joint scaling tests showed that observed variation in each host or parasite trait consisted of additive and dominance components, suggesting possible progress could be made with appropriate selection schemes. 相似文献