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Quantitative Resistance (quantitative + resistance)

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Life Sciences	100%

Selected Abstracts

Quantitative resistance to Plum pox virus in Prunus davidiana P1908 linked to components of the eukaryotic translation initiation complex

PLANT PATHOLOGY, Issue 3 2009
G. Marandel
A complex, polygenic resistance to Plum pox virus (PPV) was previously described in a wild peach-related species, Prunus davidiana clone P1908. In the current study, an analysis of quantitative trait loci (QTL) was performed on an F2 population comprising 99 individuals obtained by selfing the F1 individual #40 of an interspecific cross between susceptible nectarine cv. Summergrand and the resistant P. davidiana clone P1908. Six QTL were identified using both parametric and non-parametric methods of detection, individually explaining 5,28% of the phenotypic variance. The total phenotypic variation explained ranged from 29 to 58%. Alignment of the genetic map of the F2 cross with the P. davidiana parent map showed consistency of QTL over generations, with three of the six QTL co-localizing at the 1-LOD interval and another one at the 2-LOD interval. Two of the QTL were mapped onto linkage group one, where resistance to PPV was previously mapped in apricot. Development and mapping of new microsatellite markers linked to candidate genes revealed a striking co-localization of three of the detected QTL with gene copies coding for eukaryotic translation initiation factors eIF4E and eIF(iso)4G. As co-localization of one QTL with candidate gene eIF(iso)4E was previously reported in the F1 population, the results reported here strongly reinforce the idea that components of the eukaryotic translation initiation complex are correlated with resistance to PPV in P. davidiana P1908. [source]

Quantitative resistance to symptomless growth of Leptosphaeria maculans (phoma stem canker) in Brassica napus (oilseed rape)

PLANT PATHOLOGY, Issue 2 2009
Y. J. Huang
Quantitative resistance to Leptosphaeria maculans in Brassica napus was investigated in field and controlled environments using cultivars Darmor (with quantitative resistance) and Eurol (without quantitative resistance). In field experiments, numbers of phoma leaf spot lesions in autumn/winter and severity of stem canker the following summer were assessed in three growing seasons. There were no differences between Darmor and Eurol in number of leaf lesions in autumn/winter. However, stem cankers were less severe on Darmor than Eurol at harvest the following summer. In controlled-environment experiments, development of leaf lesions at different temperatures (5,25°C) and wetness durations (12,72 h) was investigated using ascospore inoculum; symptomless growth of L. maculans along leaf petioles towards the stem was quantified using quantitative PCR and visualized using GFP-expressing L. maculans; growth of L. maculans within stem tissues was investigated using GFP-expressing L. maculans. There were more leaf lesions on Darmor than Eurol, although there was no difference between Darmor and Eurol in L. maculans incubation period. There were no differences between Darmor and Eurol in either distance grown by L. maculans along leaf petioles towards the stem or quantity of L. maculans DNA in leaf petioles, but L. maculans colonized stem tissues less extensively on Darmor than Eurol. It was concluded that quantitative resistance to L. maculans operates during colonization of B. napus stems by the pathogen. [source]

FAMILY-LEVEL COVARIATION BETWEEN PARASITE RESISTANCE AND MATING SYSTEM IN A HERMAPHRODITIC FRESHWATER SNAIL

EVOLUTION, Issue 7 2002
Jürgen Wiehn
Abstract Genetic compatibility, nonspecific defenses, and environmental effects determine parasite resistance. Host mating system (selfing vs. outcrossing) should be important for parasite resistance because it determines the segregation of alleles at the resistance loci and because inbreeding depression may hamper immune defenses. Individuals of a mixed mating hermaphroditic freshwater snail, Lymnaea ovata, are commonly infected by a digenetic trematode parasite, Echinoparyphium recurvatum. We examined covariation between quantitative resistance to novel parasites and mating system by exposing snail families from four populations that differed by their inbreeding coefficients. We found that resistance was unrelated to inbreeding coefficient of the population, suggesting that the more inbred populations did not carry higher susceptibility load than the less inbred populations. Most of the variation in resistance was expressed among the families within the populations. In the population with the lowest inbreeding coefficient, resistance increased with outcrossing rate of the family, as predicted if selfing had led to inbreeding depression. In the other three populations with higher inbreeding coefficients, resistance was unrelated to outcrossing rate. The results suggest that in populations with higher inbreeding some of the genetic load has been purged, uncoupling the predicted relationship between outcrossing rate and resistance. Snail families also displayed crossing reaction norms for resistance when tested in two environments that presented low and high immune challenge, suggesting that genotype-by-environment interactions are important for parasite resistance. [source]

First-generation SNP/InDel markers tagging loci for pathogen resistance in the potato genome

PLANT BIOTECHNOLOGY JOURNAL, Issue 6 2003
Andreas M. Rickert
Summary A panel of 17 tetraploid and 11 diploid potato genotypes was screened by comparative sequence analysis of polymerase chain reaction (PCR) products for single nucleotide polymorphisms (SNPs) and insertion-deletion polymorphisms (InDels), in regions of the potato genome where genes for qualitative and/or quantitative resistance to different pathogens have been localized. Most SNP and InDel markers were derived from bacterial artificial chromosome (BAC) insertions that contain sequences similar to the family of plant genes for pathogen resistance having nucleotide-binding-site and leucine-rich-repeat domains (NBS-LRR-type genes). Forty-four such NBS-LRR-type genes containing BAC-insertions were mapped to 14 loci, which tag most known resistance quantitative trait loci (QTL) in potato. Resistance QTL not linked to known resistance-gene-like (RGL) sequences were tagged with other markers. In total, 78 genomic DNA fragments with an overall length of 31 kb were comparatively sequenced in the panel of 28 genotypes. 1498 SNPs and 127 InDels were identified, which corresponded, on average, to one SNP every 21 base pairs and one InDel every 243 base pairs. The nucleotide diversity of the tetraploid genotypes (, = 0.72 × 10,3) was lower when compared with diploid genotypes (, = 2.31 × 10,3). RGL sequences showed higher nucleotide diversity when compared with other sequences, suggesting evolution by divergent selection. Information on sequences, sequence similarities, SNPs and InDels is provided in a database that can be queried via the Internet. [source]

Late blight resistance in a diploid full-sib potato family

PLANT BREEDING, Issue 4 2004
S. Costanzo
Abstract Late blight, caused by Phytophthora infestans (Mont.) de Bary, is the most destructive disease of potato worldwide. As this pathogen can rapidly overcome major race-specific resistance genes, identifying the basis for enhanced quantitative resistance has become a crucial element for implementing advanced breeding strategies. A population of 230 full-sib progeny derived from a cross between two diploid hybrid Solanum phureja × S. stenotomum clones was evaluated for foliage resistance against late blight in replicated trials at multiple locations in Pennsylvania between 1999 and 2002. In field experiments, plants were evaluated visually for per cent defoliation, and area under the disease progress curve (AUDPC) was determined. The two parents and three control cultivars (,Atlantic', ,Kennebec' and ,Katahdin') were included in all trials. In all three experiments, the presence of a significant number of clones exhibiting transgressive segregation were observed. There were significant differences among environments as well as among clones, and the clone × environment interaction was also significant. Stability analysis revealed that 37 clones made a significant contribution to the overall environment × clone interaction. Broad-sense heritability for resistance, measured as AUDPC, was estimated as 0.67. The overall results indicate the presence in this potato family of a high level of field resistance against late blight. This segregating diploid family appears to be a good candidate for quantitative trait loci mapping to identify and characterize the genetic components of partial late blight resistance. [source]

Potential of Eurasian poplar rust to overcome a major quantitative resistance factor

PLANT PATHOLOGY, Issue 3 2010
A. Dowkiw
The effect of RUS, a major quantitative resistance (QR) factor inherited from Populus trichocarpa, was assessed in two Populus deltoides × P. trichocarpa F1 progenies against eight isolates of Melampsora larici-populina, the causal agent of Eurasian poplar rust. Six isolates were identified on which RUS had no significant effect. The first RUS -defeating isolate identified suggested a pre-existing potential to overcome RUS in the pathogen's populations. The P. deltoides genetic background made no difference either to the ability of a given isolate to overcome RUS or to the relative and absolute aggressiveness of the isolates. This study illustrates how extreme the isolate-specificity of QR can be. It also yields insights into the relationship between size of uredinia and sporulation rate, discussing the epidemiological significance of spore production per mm2 uredinium. [source]

Quantitative resistance to symptomless growth of Leptosphaeria maculans (phoma stem canker) in Brassica napus (oilseed rape)

Expression of resistance to Leptosphaeria maculans in Brassica napus double haploid lines in France and Australia is influenced by location

ANNALS OF APPLIED BIOLOGY, Issue 2 2008
R. Delourme
Abstract Blackleg, caused by Leptosphaeria maculans, is a major disease of oilseed rape (Brassica napus), worldwide, including Australia and France. The aims of these studies were first, to determine if higher levels of resistance to L. maculans could be generated in double haploid (DH) lines derived from spring-type B. napus cv. Grouse, which has a good level of field resistance to blackleg; and second, to determine whether the resistance to blackleg disease of individual DH lines responds differentially to different L. maculans field populations within and between the two countries. DH lines were extracted from cv. Grouse and tested in field experiments carried out in both France and Australia against natural L. maculans populations. Extracting and screening DH lines were an effective means to select individual lines with greatly improved expression of resistance to blackleg crown canker disease in comparison with the original parental population. However, relative disease resistance rankings for DH lines were not always consistent between sites. The higher level of resistance in France was shown to be because of a high expression level of quantitative resistance in the French growing conditions. Big differences were observed for some DH lines between the 2004 and the 2005 field sites in Australia where the L. maculans populations differed by their virulence on single dominant gene-based resistant lines derived from Brassica rapa ssp. sylvestris. This differential behaviour could not be clearly explained by the specific resistance genes until now identified in these DH lines. This investigation highlights the potential to derive DH lines with superior levels of resistance to L. maculans compared with parental populations. However, in locations with particularly high pathogen diversity, such as in southern Australia, multiyear and multisite evaluations should be performed to screen for the most efficient material in different situations. [source]