Showing papers on "Plant disease resistance published in 1992"
TL;DR: Mlo resistance to barley powdery mildew is a relatively new kind of resistance that does not conform to the gene-for-gene system and is caused by rapid formation of large cell wall appositions at the encounter sites preventing penetration by the fungus.
Abstract: 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.
505 citations
TL;DR: An efficient gene transfer system utilizing microprojectile-mediated transformation of 2,4-D-treated immature zygotic embryos with a plasmid construction that contains the neomycin phosphotransferase II and β-glucuronidase genes flanking a PRV cp gene expression cassette is reported.
Abstract: Papaya ringspot virus (PRV) is a serious disease of papaya (Carica papaya L.) that has only been partially controlled by conventional methods. An alternative control method is coat protein-mediated protection (CPMP) through the transfer and expression of the PRV coat protein (cp) gene in papaya. We report an efficient gene transfer system utilizing microprojectile-mediated transformation of 2,4-D-treated immature zygotic embryos with a plasmid construction that contains the neomycin phosphotransferase II (NPTII) and β-glucuronidase (GUS) genes flanking a PRV cp gene expression cassette. Putative transgenic RO papaya plants, regenerated on kanamycin-containing medium, were assayed for GUS and PRV coat protein expression, for the presence of NPTII and PRV cp genes [with the polymerase chain reaction (PCR) and genomic blot hybridization analysis], and for PRV cp gene transcripts by Northern analysis. Four RO transgenic plant lines that contained the PRV cp gene showed varying degrees of resistance to PRV, and one line appeared to be completely resistant. These results represent the first demonstration that CPMP can be extended to a tree species such as papaya.
324 citations
TL;DR: Although Mendel published his genetic studies on peas in 1866 it was not until the end of the last century that his work was understood and taken up by other scientists and caused a breakthrough in breeding for disease resistance and the understanding of the genetics of plant-fungus interactions.
Abstract: Although Mendel published his genetic studies on peas in 1866 it was not until the end of the last century that his work was understood and taken up by other scientists. In 1898, Farrer (48) discovered that resistance to rust in wheat is inherited. Biffen's discovery in 1905 (9) that resistance to yellow rust (Puccinia striiformis) in wheat obeys Mendel's laws caused a breakthrough in breeding for disease resistance and the understanding of the genetics of plant-fungus interactions. The optimism induced by Biffen's studies led him and other scientists to the conclusion that resistance to this fungus would be durable, as it was expected that the fungus would evolve too slowly to overcome the introduced resistance gene. Only a decade later, however, Stakman and coworkers (126, 127), studying resistance in wheat to wheat stem rust (Puccinia graminis f . sp. trifici), were able to show that resistance
296 citations
293 citations
01 Jan 1992
TL;DR: Unlike chordate animals, plants have not evolved a single primary mechanism for dealing with a broad spectrum of pathogens, so they have resorted to a variety of structural and biochemical defense mechanisms more or less tailored to individual pathogens.
Abstract: Unlike chordate animals, plants have not evolved a single primary mechanism for dealing with a broad spectrum of pathogens. Instead, plants have resorted to a variety of structural and biochemical defense mechanisms more or less tailored to individual pathogens. Many of the structures and compounds associated with the resistance of plants to pathogenic infection have been identified and studied for decades by plant pathologists, physiologists and biochemists. Similarly, genetic variation has been noted between plant lines in resistance to particular plant pathogens or pathogen races for most of the plant::pathogen interactions that have been studied. And, in over 200 cases, the differential susceptibility has been attributed to allelic variation at major resistance (or “R”) genes. Surprisingly, in only two cases have inherited resistances been clearly associated with the presence or absence of an identified biochemical resistance activity, and neither of these seem to be a common mechanism of resistance (1,2).
238 citations
TL;DR: Reduced severity of grape mildew by Si sprays may be partly due to a physical barrier to hyphal penetration and to a resistance response involving the lateral movement of Si and its deposition within the leaf at fungal penetration sites.
Abstract: The effect of root or leaf applications of soluble Si on severity of grape (Vitis vinifera L.) powdery mildew (Uncinula necator (Schwein) Burrill) was determined. On potted plants, root-feeding at 1.7 m M Si had no effect on disease severity, but foliar sprays at 17 m M Si substantially reduced the number of mildew colonies that developed on inoculated leaves. Scanning electron micrographs showed that, on Si-sprayed leaves, hyphae did not develop in areas where thick Si deposits were present on the leaf surface; and where surface deposits were not present, Si was translocated laterally through the leaf and surrounded the appressoria. Leaves on plants that were fed Si via roots showed a similar deposition of Si surrounding the appressoria. On water-sprayed leaves and leaves from untreated plants, internal deposition of Si was more variable and generally less than on Si-sprayed or root-fed plants. Conidia germination and germtube development on agar media were weakly promoted by the presence of Si. Reduced severity of grape mildew by Si sprays may be partly due to a physical barrier to hyphal penetration and to a resistance response involving the lateral movement of Si and its deposition within the leaf at fungal penetration sites. In monocot crops, the association between Si and reduced severity of fungal diseases has been known for some time. Ger- mar (1934) reported that wheat (Triticum aestivum L.) plants supplied with Si are more resistant to powdery mildew (Erysiphe graminis f. sp. hordei) than control plants. Since then, Si has been implicated in several other monocot disease resistance re- sponses, including sorghum (Sorghum vulgare Pert.) resistance to anthracnose (Colletotricum graminicolum) (Narwal, 1973), barley (Hordium vulgare L.) and wheat resistance to powdery mildew (E. graminis f. sp. hordei) (Jiang et al., 1989; Kunoh and Ishizaki, 1976; Leusch and Buchenauer, 1989; Sargent and Gay, 1977), and rice (Oryza sativa L.) resistance to blast (Pir- icularia oryzae Cav.), brown spot (Bipolaris oryzae Shoemaker) and sheath blight (Corticium sasakii Shiriai) (Aleshin et al., 1986; Datnoff and Snyder, 1991; Mathai et al., 1978; Volk et al., 1958). The exact role silica plays in enhancing disease re- sistance in monocots is as yet undetermined, but localized de- posits of Si have been found in host tissue surrounding fungal haustoria (Kunoh and Ishizaki, 1976; Sargent and Gay, 1977). In dicots, less attention has been paid to the association be- tween Si and resistance to fungal infection. Although Wagner (1940) reported that cucumber powdery mildew severity was reduced by supplying plants with Si, current interest in this phenomenon was not spawned until the mid-1980s, when it was reported that the natural incidence of powdery mildew was re- duced by feeding Si to solution-cultured cucumbers (Adatia and Besford, 1986; Miyake and Takahashi, 1983). The reduction in
234 citations
TL;DR: The simultaneous presence of Lr34 and leaf tip necrosis in the two Thatcher near-isogenic lines and Mexican cultivars was confirmed by evaluating F ₂ plants or F₃ lines obtained from various intercrosses.
Abstract: Durable resistance to leaf rust (Puceinia recondita Roberge ex Desmaz. f. sp. tritici) in bread wheat (Triticum oestivurn L.) cultivars is known to result from the interaction of Lr34 with other minor additive genes that are effective in the adult growth state. The Lr34 gene seems to be present in several CIMMYT germplasm-derived Mexican cultivars that display temperature- and light-sensitive seedling responses similar to those displayed by near-isogenic ‘Thatcher’ lines that contain Lr34. Adult plants of these two Thatcher lines and all Mexican cultivars postulated to carry Lr34 display resistance to leaf rust and exhibit leaf tip necrosis symptoms. This study was conducted to determine whether 15-34 and a gene or genes for leaf tip necrosis am linked. The simultaneous presence of Lr34 and leaf tip necrosis in the two Thatcher near-isogenic lines and Mexican cultivars was confirmed by evaluating F₂ plants or F₃ lines obtained from various intercrosses. Lr34 and leaf tip necrosis were inherited together in a population of 117 F₃ lines obtained from the cross of leaf rust resistant ‘Jupateco 73R’ (carrying Lr34 and leaf tip necrosis) with its susceptible counterpart ‘Jupateco 73s’. Linkage or pleiotropism was also evident in the crosses of six Lr34-carrying Mexican cultivars with ‘Siete Cerros 66’ (which does not have Lr34). The gene for leaf tip necrosis, designated Lln, could be used as a marker for Lr34.
224 citations
TL;DR: Backcross progeny produced from interspecific hybrids of O. sativa cv ‘IR31917-45-3-2’ and O. minuta Acc.
Abstract: Oryza minuta J. S. Presl ex C. B. Presl is a tetraploid wild rice with resistance to several insects and diseases, including blast (caused by Pyricularia grisea) and bacterial blight (caused by Xanthomonas oryzae pv. oryzae). To transfer resistance from the wild species into the genome of cultivated rice (Oryza sativa L.), backcross progeny (BC1, BC2, and BC3) were produced from interspecific hybrids of O. sativa cv 'IR31917-45-3-2' (2n=24, AA genome) and O. minuta Acc. 101141 (2n=48, BBCC genomes) by backcrossing to the O. sativa parent followed by embryo rescue. The chromosome numbers ranged from 44 to 47 in the BC1 progeny and from 24 to 37 in the BC2 progeny. All F1 hybrids were resistant to both blast and bacterial blight. One BC1 plant was moderately susceptible to blast while the rest were resistant. Thirteen of the 16 BC2 progeny tested were resistant to blast; 1 blast-resistant BC2, plant 75-1, had 24 chromosomes. A 3 resistant: 1 susceptible segregation ratio, consistent with the action of a major, dominant gene, was observed in the BC2F2 and BC2F3 generations. Five of the BC1 plants tested were resistant to bacterial blight. Ten of the 21 BC2 progeny tested were resistant to Philippine races 2, 3, and 6 of the bacterial blight pathogen. One resistant BC2, plant 78-1, had 24 chromosomes. The segregation of reactions of the BC2F2, BC2F3, and BC2F4 progenies of plant 78-1 suggested that the same or closely linked gene(s) conferred resistance to races 2, 3, 5, and 6 of the bacterial blight pathogen from the Philippines.
222 citations
TL;DR: The contribution of introgressed regions derived from wild species to the genetic variation within the species of Lycopersicon esculentum was investigated by comparing the RFLP patterns of 2 introgression-free, obsolete cultivars and a modern cultivar that carries at least 5 introgressive resistance genes.
Abstract: The contribution of introgressed regions derived from wild species to the genetic variation within the species of Lycopersicon esculentum was investigated by comparing the RFLP patterns of 2 introgression-free, obsolete cultivars ('Moneymaker' and 'Premier') and a modern cultivar ('Sonatine') that carries at least 5 introgressed resistance genes. In this analysis 195 mapped nuclear markers were used in combination with 6 restriction enzymes. Among the 1170 probe-enzyme combinations tested, only 3 showed a polymorphism between the 2 introgression-free cultivars. On the other hand 24 probe-enzyme combinations were found to exhibit polymorphisms between 'Moneymaker' and 'Sonatine'. These represented ten polymorphic loci distributed among 5 linkage groups on chromosomes 1, 3, 4, 6, and 9.On the assumption that most of the polymorphic loci corresponded to introgressed chromosome segments of wild species carrying resistance genes, linkages between these loci and the component resistance genes were examined by RFLP analysis of pairs of near-isogenic lines differing only for one particular resistance gene, and a variety of commercial cultivars having different resistance gene compositions. Two of the polymorphic linkage groups could thus be ascribed to resistance genes whose map positions were already known: Cf2 on chromosome 6 and Tm2a on chromosome 9, whereas another marker, TG301 on chromosome 1, could be assigned to the Cladosporium fulvum resistance gene Cf9 with a hitherto disputable map position. By linkage analysis of a segregating F2 population the genetic distance between the Cf9 gene and the marker TG301 was estimated at 5.5 ± 2.3 cM.
187 citations
TL;DR: It is reported here that the repetitive region of the avrBs3 gene determines race-specificity and that deletions of repeat units generate new avirulence specificities and unmask undiscovered resistance genes in pepper and tomato.
Abstract: ELUCIDATION of the genetic and molecular basis of plant disease resistance is a major objective in the investigation of plant-micro-bial interactions. Xanthomonas campestris pathovar vesicatoria (Xcv), the causal agent of bacterial spot disease of pepper and tomato, has been developed as a model host–pathogen system to study the genetic interactions that specify the expression of plant disease resistance1–6. Several plant resistance genes (Bsl, Bs2, Bs3) have been genetically characterized from pepper (Capsicum annuum) that determine resistance to particular races of the pathogen carrying specific avirulence genes7–9. For example, pepper plants carrying the resistance locus Bs3 are resistant to Xcv strains expressing the avirulence gene avrBs3. Nucleotide sequence analysis of the avrBs3 gene revealed that the internal portion of the predicted protein product consists of a nearly identical 34 amino acid repeat unit, present in 17.5 copies4. We report here that the repetitive region of the avrBs3 gene determines race-specificity and that deletions of repeat units generate new avirulence specificities and unmask undiscovered resistance genes in pepper and tomato.
183 citations
TL;DR: It is demonstrated that CP-mediated resistance to virus infection can be extended to cereals and to the viruses transmitted by an insect vector (planthopper).
Abstract: The coat protein (CP) gene of rice stripe virus was introduced into two japonica varieties of rice by electroporation of protoplasts. The resultant transgenic plants expressed the CP at high levels (up to 0.5% of total soluble protein) and exhibited a significant level of resistance to virus infection. Plants derived from selfed progeny of the primary transformants also expressed the CP and showed viral resistance, indicating stable transmission of the CP gene and the trait of resistance to the next generation. Moreover, the virally encoded strip disease-specific protein was not detected in transgenic plants expressing CP 8 weeks after inoculation, indicating protection before viral multiplication. These studies demonstrated that CP-mediated resistance to virus infection can be extended to cereals and to the viruses transmitted by an insect vector (planthopper).
TL;DR: It is demonstrated that a bacterial avirulence (avr) gene function, avrPpiA1, from the pea pathogen Pseudomonas syringae pv pisi, is recognized by some, but not all, genotypes of Arabidopsis, and therefore bean, pea, and conceivably other crop species contain functional and potentially molecular homologs of RPM1.
Abstract: We showed that a bacterial avirulence (avr) gene function, avrPpiA1, from the pea pathogen Pseudomonas syringae pv pisi, is recognized by some, but not all, genotypes of Arabidopsis. Thus, an avr gene functionally defined on a crop species is also an avr gene on Arabidopsis. The activity of avrPpiA1 on a series of Arabidopsis genotypes is identical to that of the avrRpm1 gene from P.s. pv maculicola previously defined using Arabidopsis. The two avr genes are homologous and encode nearly identical predicted products. Moreover, this conserved avr function is also recognized by some bean and pea cultivars in what has been shown to be a gene-for-gene manner. We further demonstrated that the Arabidopsis disease resistance locus, RPM1, conditioning resistance to avrRpm1, also conditions resistance to bacterial strains carrying avrPpiA1. Therefore, bean, pea, and conceivably other crop species contain functional and potentially molecular homologs of RPM1.
TL;DR: It is shown genetically that ELI3 activation is strictly dependent on the presence of dominant alleles at RPM1 using an assay generalizable to any pathogen induced plant defense phenomena.
Abstract: We cloned and sequenced cDNAs encoded by a novel plant defense gene, ELI3, from parsley and Arabidopsis thaliana. The predicted product shares no homology to known sequences. ELI3 mRNA accumulates in A. thaliana leaves in response to challenge with phytopathogenic Pseudomonas syringae strains. The timing and magnitude of this response are dictated by the genetics of the plant-pathogen interaction being analyzed. During incompatible interactions, where resistance in the plant genotype Col-0 is dictated by the dominant RPM1 locus, ELI3 mRNA accumulates to high levels 5-10 h post-inoculation. This kinetic behavior is also generated by the presence of a cloned bacterial avirulence gene, in otherwise virulent bacteria, which triggers resistance mediated via RPM1 action. The phenotypic outcome is a hypersensitive resistance reaction visible 8-15 h post-infiltration. Thus, the induction kinetics of ELI3 mRNA accumulation are consistent with a functional role for the ELI3 gene product in establishing the resistant phenotype. In contrast, during compatible interactions with the susceptible plant genotype Nd-0, which is homozygous recessive at the rpm1 locus, ELI3 mRNA accumulates significantly only after 15 h. We show genetically that ELI3 activation is strictly dependent on the presence of dominant alleles at RPM1 using an assay generalizable to any pathogen induced plant defense phenomena.
TL;DR: It is suggested that new technology will enhance breeding for disease resistance but that established techniques of plant breeding will remain relevant and important.
Abstract: 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.
TL;DR: This is the first report of the successful integration of a viral coat protein gene into a fruit tree species, opening a new perspective on the control of the disease.
Abstract: A system was developed which allows the transfer of foreign genes into apricot cultivars. We report the transformation and regeneration of Prunus armeniaca plants with Agrobacterium tumefaciens strain LBA 4404 containing various binary plasmids, pBinGUSint, carrying the marker gene s-glucuronidase (GUS) and pBinPPVm, carrying the coat protein gene of Plum Pox Virus (PPV). The marker gene GUS was used for optical evaluation of the efficiency of the transformation system. The coat protein gene of PPV was used to introduce coat protein mediated resistance against one of the most important pathogens of stone fruit trees in Europe and the whole Mediterranean area. This is the first report of the successful integration of a viral coat protein gene into a fruit tree species, opening a new perspective on the control of the disease.
TL;DR: Full-length cDNA clones of potato virus X (PVX) strains PVXUK3 and PVXHB have been constructed in plasmid vectors to allow in vitro transcription of infectious PVX RNA, and the coat protein gene is therefore the determinant of Nx and Rx resistance breaking of PVX HB.
TL;DR: Inheritance of stripe rust resistance in 13 wheat cultivars used to differentiate races of Puccinia striiformis in North America was determined using nine North American races of the pathogen.
Abstract: Inheritance of stripe rust resistance in 13 wheat (Triticum aestivum) cultivars used to differentiate races of Puccinia striiformis in North America was determined using nine North American races of the pathogen. The differential cultivars, which were resistant to specific races, were crossed with cultivars susceptible to the specific races. We found that Lemhi, Chinese 166, Riebesel 47/51, and Tyee each have a single resistance gene; Heines VII, Moro, Druchamp, Produra, Stephens, Lee, and Fielder each have two resistance genes; and Paha and Yamhill each have three resistance genes (...)
TL;DR: Resistance to 56 viruses in the family Potyviridae in 334 plant species was tabulated and the role of conventional breeding and biotechnology in transferring genes from one species to another is discussed.
Abstract: Resistance to 56 viruses in the family Potyviridae in 334 plant species was tabulated. Studies conducted in the last 60 years have elucidated the genetics and usefulness of 135 resistance genes, but no reports on the heritability of other sources of resistance are available. In most of the plant species, resistance to species of Potyviridae was simply inherited, either dominantly (60 genes) or recessively (39 genes). In some cases resistance was conferred by two or more genes. Symbols have been assigned to 86 genes, of which very few are duplicate entities. Resistance genes can be useful in determining relationships among these viruses, as well as for their identification. The role of conventional breeding and biotechnology in transferring genes from one species to another is discussed.
TL;DR: The results demonstrate the commercial feasibility of improving potato cultivars by selectively adding new traits while preserving intrinsic properties, and the possibility of unambiguously identifying independent transgenic cultivars.
Abstract: Increased Resistance to Potato Virus X and Preservation of Cultivar Properties in Transgenic Potato Under Field Conditions
TL;DR: This is the first conclusive report of the stable transfer of disease resistance and DNA from H. bulbosum to H. vulgare and the progenies produced could serve as an important resistant source in plant breeding.
Abstract: In an attempt to transfer traits of agronomic importance from H. bulbosum into H. vulgare we carried out crosses between four diploid barley cultivars and a tetraploid H. bulbosum. Eleven viable triploid F1 plants were produced by means of embryo rescue techniques. Meiotic pairing between H. vulgare and H. bulbosum chromosomes was evidenced by the formation of trivalents at a mean frequency of 1.3 with a maximum of five per cell. The resulting triploid hybrids were backcrossed to diploid barley, and nine DC1 plants were obtained. Three of the BC1 plants exhibited H. bulbosum DNA or disease resistance. A species specific 611-bp DNA probe, pSc119.2, located in telomeres of the H. bulbosum genome, clearly detected five H. bulbosum DNA fragments of about 2.1, 2.4, 3.4, 4.0 and 4.8 kb in size present in one of the BC1 plants (BC1-5) in BamHI-digested genomic Southern blots. Plant BC1-5 also contained a heterozygous chromosomal interchange involving chromosomes 3 and 4 as identified by N-banding. One of the two translocated chromosomes had the H. bulbosum sequence in the telomeric region as detected using in situ hybridization with pSc119.2. Two other BC1 plants (BC1-1 and BC1-2) were resistant to the powdery mildew isolates to which the barley cultivars were susceptible. Seventy-nine BC2 plants from plant BC1-2 segregated 32 mildew resistant to 47 susceptible, which fits a ratio of 1∶1, indicating that the transferred resistance was conditioned by a single dominant gene. Reciprocal crosses showed a tendency towards gametoselection that was relative to the resistance. Mildew resistant plant BC1-2 also had a 1-kb H. bulbosum DNA fragment identified with a ten-base random primer using polymerase chain reaction (PCR). Forty-three BC1 plants, randomly sampled from the 79 BC1 plants, also segregated 23∶20 for the presence versus absence of this 1-kb H. bulbosum DNA fragment, thereby fitting a 1∶1 ratio and indicating that the PCR product originated from a single locus. The 1-kb DNA fragment and disease resistance were independently inherited as detected by PCR analysis of bulked DNA from 17 resistant and 17 susceptible plants as well as by trait segregation in the 43 individual plants. The progenies produced could serve as an important resistant source in plant breeding. This is the first conclusive report of the stable transfer of disease resistance and DNA from H. bulbosum to H. vulgare.
TL;DR: The results show that the leaf rust resistance gene(s), designated Lr38, is located in the distal half of the long arm of chromosome 7Ai-2, whereas the genes for resistance to stem rust and stripe rust are located either in the short arm or in the proximal region of theLong arm of this chromosome.
Abstract: Chromosome constitutions of three wheat-Agropyron intermedium derivatives were identified by C-banding analysis, in situ hybridization using biotin-labeled genomic Ag. intermedium DNA as a probe and isozyme analysis. Lines W44 and W52 were identified as 7Ai-2(7D) and 7Ai-2(7A) chromosome substitution lines carrying the same chromosome pair of Ag. intermedium. The alien chromosome was found to be homoeologous to group 7 based on C-banding, meiotic pairing and isozyme analyses. Line W49 was identified as a wheat Ag. intermedium chromosome translocation line. The breakpoint of the T2AS · 2AL-7Ai-2L translocation is located in the long arm at a fraction length of 0.62, and the transferred Ag. intermedium segment has a size of about 2.4 μm. Lines W44 and W52 expressed Ag. intermedium genes for resistance to leaf rust, stripe rust and stem rust, but only leaf rust resistance was expressed in W49. The results show that the leaf rust resistance gene(s), designated Lr38, is located in the distal half of the long arm of chromosome 7Ai-2, whereas the genes for resistance to stem rust and stripe rust are located either in the short arm or in the proximal region of the long arm of this chromosome.
TL;DR: Synthetic lines of Brassica napus were derived by combining the genomes of B. atlantica and B. oleracea var.
Abstract: Synthetic lines of Brassica napus were derived by combining the genomes of B. atlantica and B. oleracea var. alboglabra, which were respectively resistant and susceptible to foliar infection by Leptosphaeria maculans, with a susceptible line of B. rapa. Resistance was expressed in the synthetic lines containing the genome of B. atlantica. The high levels of alkenyl glucosinolates which occur in leaves of B. atlantica, and which have been implicated in disease resistance, were also expressed within the synthetic lines, although the dominant glucosinolate had changed from sinigrin to glucobrassicanapin. Disease resistance and glucosinolate profiles did not co-segregate in F2 progeny from crosses between the synthetic lines.
TL;DR: An Rps allele in the Harosoy cultivar of soybean (Glycine max) for resistance to races 16, 18, and 19 of Phytophthora megasperma f.
Abstract: An Rps allele in the Harosoy cultivar of soybean (Glycine max) for resistance to races 16, 18, and 19 of Phytophthora megasperma f. sp. glycinea was shown to be at a new locus, designated Rps7, which is linked 12.5±2.7 map units from Rps1 in Linkage Group 10
TL;DR: Segregation ratios in the F2 generation of 13 resistant to 3 susceptible plants fit a 2-gene model for resistance with dominant and recessive epistasis.
Abstract: Inheritance studies were conducted to determine the genetic basis of adult-plant resistance in pepper (Capsicum annuum L.) to Phytophthora capsici. F1, backcrosses and F2 populations were developed using the resistant parent Criollo de Morellos 334 and susceptible parents Agronomico 10-G and Yolo Wonder. Pepper plants, at 36 days post-emergence, were inoculated near the base of the stem with an inoculum suspension of 5×104 zoospores/ml. Segregation ratios in the F2 generation of 13 resistant to 3 susceptible plants fit a 2-gene model for resistance with dominant and recessive epistasis.
TL;DR: To study the effects of leaf age on resistance, plants of four rice cultivars were inoculated with a virulent isolate of Pyricularia oryzae, and susceptibility of leaves declined rapidly with increasing leaf age, but resistance in leaves rapidly increased with age.
Abstract: To study the effects of leaf age on resistance, plants of four rice cultivars were inoculated with a virulent isolate of Pyricularia oryzae. Susceptibility of leaves declined rapidly with increasing leaf age. In older leaves, fewer sporulating lesions developed per unit of leaf area, and eventually leaves became completely resistant. The period during which newly formed leaves were susceptible, as well as the initial level of susceptibility of new leaves, differed greatly between cultivars. Cultivars with high levels of partial resistance to leaf blast showed typical susceptible lesions, but the resistance in leaves rapidly increased with age, and the initial level of susceptibility of new leaves was low
TL;DR: The gametic frequency of a dominant allele (R) for resistance to white pine blister rust, a disease caused by an introduced pathogen (Cronartium ribicola), in natural populations of sugar pine was studied.
Abstract: The gametic frequency of a dominant allele (R) for resistance to white pine blister rust, a disease caused by an introduced pathogen (Cronartium ribicola), in natural populations of sugar pine was ...
TL;DR: Accessions of 12 perennial Glycine species were evaluated for resistance to Phakopsora pachyrhizi, the causal agent of soybean rust, finding resistance was identified in accessions of G. arenaria, G. cyrtoloba, and G. tabacina.
Abstract: Accessions of 12 perennial Glycine species were evaluated for resistance to Phakopsora pachyrhizi, the causal agent of soybean rust. A total of 23% of the accessions were resistant, 18% were moderately resistant, and 58% were susceptible. In two experiments, 59 and 40% of the accessions of G. tabacina (2n=80) were resistant. Resistance to P. pachyrhizi was identified in accessions of G. argyrea, G. canescens, G. clandestina, G. latifolia, G. microphylla, and G. tomentella, but not in accessions of G. arenaria, G. cyrtoloba, G. curvata, and G. falcata
01 Jan 1992