Disease resistance. Eyespot
Contributed by Dipak K. Santra, Kim Kidwell and Kimberly Campbell
References
1. Resistance to benzimidazole fungicides in the cereal eyespot pathogen, Pseuudocercosporella herpotrichoides, in the U.S. Pacific Northwest 1984 to 1990. Murray T.D. In: Plant Disease,1996, 80: 19-23.
Isolates of P. herpotrichoides tolerant of benzimidazole fungicides were detected in commercial winter wheat fields in the Pacific Northwest region (Washington, Oregon and Idaho) of the USA for the first time in the spring of 1989. Benzimidazole-tolerant isolates were found in 9 of 62 fields sampled in 1989 and in 17 of 167 fields sampled in 1990, respectively, 96 and 70% of all isolates collected from fields where fungicide tolerance was detected were tolerant of benzimidazole fungicides. All fields where fungicide-tolerant strains of P. herpotrichoides were found had at least 4 previous applications of a benzimidazole fungicide. In 1989 and 1990, respectively, 24 and 15% of the P. herpotrichoides cultures collected had a slow growth rate with feathery colony margins on potato-dextrose agar and corresponded to rye-type isolates. However, benzimidazole-tolerant rye-type isolates only represented 7 and 4% of the total tolerant isolates collected in 1989 and 1990, respectively.
2. Genome origin of Triticum cylindricum, Triticum triunciale, and Triticum ventricosum (Poaceae) inferred from variation in repeated nucleotide sequences: a methodological study. Dubcovsky J, Dvorak J In: American Journal of Botany, 1994, 81:1327-1335
3. Identification of an RFLP interval containing Pch2 on chromosome 7AL of wheat.de la Pena RC, Murray TD, Jones SS. In: Genome, 1997, 40: 249-252.
The gene Pch2 in Triticum aestivum cv. Cappelle Desprez is one of two genes found in hexaploid wheat known to confer resistance to eyespot disease caused by Pseudocercosporella herpotrichoides. This study was conducted to develop an RFLP linkage map of the distal portion of wheat chromosome 7AL, and to locate and identify markers closely associated with Pch2 for use in marker-assisted selection. Ten loci in addition to Pch2 were mapped on chromosome 7AL, using segregation data from 102 homozygous chromosome 7A recombinant substitution lines derived from Chinese Spring X Chinese Spring (Cappelle Desprez 7A). The Pch2 locus was bracketed by two RFLP markers: Xcdo347 (11.0 cM distal to Pch2) and Xwg380 (18.8 cM proximal). The position of Pch2 on chromosome 7AL is similar to that of Pch1 on chromosome 7DL, suggesting that these resistance genes are homoeoloci. Although no single marker was closely linked to Pch2, simultaneous selection of the flanking RFLP markers Xcdo347 and Xwg380 could be used for selecting Pch2, since double recombination occurred in only 3% of the recombinant population. The use of the flanking RFLP markers to select for Pch2, in combination with previously identified Pch1-linked markers, would facilitate the development of cultivars carrying two genes for resistance to eyespot.
4. A new source of resistance to Pseudocercosporella herpotrichoides, cause of eyespot disease of wheat, located on chromosome 4V of Dasypyrum villosum. Murray TD, de la Peņa RC, Yildirim A, Jones SS In: Plant Breeding, 1994, 113:281-286.
Resistance to Pseudocercosporella herpotrichoides in 5 wheat cultivars, accession W6-7283 of Dasypyrum villosum and Chinese Spring disomic addition lines of the D. villosum chromosomes 1V, 2V, 4V, 5V, 6V and 7V, was evaluated in seedlings by measuring disease progress 6 weeks after inoculation with a GUS-transformed strain of the pathogen and by visual estimates of disease severity. D. villosum and the disomic addition line of chromosome 4V were as resistant as wheat cultivars VPM1 and Cappelle Desprez, but less resistant than Rendezvous. Resistance of the chromosome 4V disomic addition line was equivalent to that of D. villosum. Chinese Spring and disomic addition lines of 1V, 2V, 5V, 6V and 7V were all susceptible. These results confirm an earlier report of resistance in D. villosum to P. herpotrichoides and establish the chromosomal location for the genes controlling resistance. The presence of chromosome 4V in the addition line and its homoeology to chromosome 4 in wheat were confirmed by Southern analysis of genomic DNA using chromosome group 4-specific clones. This genetic locus is not homoeologous with other known genes for resistance to P. herpotrichoides located on chromosome group 7, and thus represents a new source of resistance to this pathogen.
5. Resistance to stripe rust and eyespot diseases of wheat in Triticum tauschii. Yildirim A, Jones SS, Murray TD, Cox TS, Line RF In: Plant Disease,1995, 79:1230-1236.
A collection of 279 T. tauschii (Aegilops squarrosa) accessions was evaluated for resistance to diseases caused by Puccinia striiformis and Pseudocercosporella herpotrichoides. Seedlings were inoculated with 4 races of P. striiformis that represented all known virulences in the Pacific Northwest, and a genetically modified strain of P. herpotrichoides expressing beta-glucuronidase. Of the A. squarrosa [T. tauschii] accessions, 17% were resistant to all Pacific Northwest races of P. striiformis, and 45% were resistant to P. herpotrichoides; 39 accessions were resistant to both diseases. Accessions resistant to P. striiformis were mainly from the Caspian Sea region of Iran and Azerbaijan, with the majority belonging to A. squarrosa subsp. strangulata and A. squarrosa var. meyeri. There was no clear association between resistance to P. herpotrichoides and geographical origin or taxonomic subgroup.
6. Identification of resistance to Pseudocercosporella herpotrichoides in Triticum monococcum. Cadle MM, Murray TD, Jones SS. In: Plant Disease, 1997, 81:1181-1186.
Genes Pch1, located on chromosome 7D, and Pch2, located on chromosome 7A, are the only known sources of eyespot, caused by P. herpotrichoides, resistance in hexaploid wheat. A core collection of Triticum monococcum, a close relative of the A-genome donor of bread wheat, consisting of 118 accessions from 26 countries was screened for resistance using a beta-glucuronidase-transformed strain of the pathogen. Fifty-two (44%) accessions from 15 different countries were resistant. More than half of the accessions collected in Turkey (26 of 42) were resistant. Two accessions were more resistant than resistant cultivars Cappelle Desprez (Pch2) and Madsen (Pch1). Screening these accessions for the isoenzyme marker Ep-A1b, which is linked with Pch2 in hexaploid wheat, revealed variation but no association with resistance. These results indicate T. monococcum is a new source of resistance to P. herpotrichoides that potentially contains more effective resistance to P. herpotrichoides than that conferred by either Pch1 or Pch2.
7. Isolation of a chromosomally engineered durum wheat line carrying the Aegilops ventricosa Pch1 gene for resistance to eyespot.. Huguet-Robert V, Dedryver F, Roder MS, Korzun V, Abelard P, Tanguy AM, Jaudeau B, Jahier J. In: Genome, 2001, 44:345-349.
The chromosome 7Dv of Aegilops ventricosa (syn. Triticum ventricosum, 2n = 4x = 28, genome DvDvMvMv) carries the gene Pch1 for resistance to eyespot. This gene has previously been transferred to chromosome 7D of bread wheat, T. aestivum (2n = 6x = 42, genome AABBDD). To (1) enhance the level of resistance of bread wheat by increasing the copy number of Pch1, and (2) create eyespot-resistant triticales, meiotically stable Pch1-carrying durum lines were selected from the backcross progenies of a cross between Ae. ventricosa and T. durum cv. Creso ph1c (2n = 4x = 28, genome AABB). The Pch1 transfer, likely resulting from homoeologous recombination, was located at the distal position on the long arm of chromosome 7A. The 7A microsatellite marker Xgwm 698 was found closely linked in repulsion to the introgression in the resistant recombination lines, and the endopeptidase allele located on chromosome 7A of cv. Creso ph1c was lost.
8. Linkage relations among eyespot resistance gene Pch2, endopeptidase Ep-A1b and RFLP marker Xpsr121 on chromosome 7A of wheat. de la Peņa RC, Murray TD, Jones SS. In: Plant Breeding, 1996, 115:273-275.
Marker-based selection of Ep-D1b was used successfully to incorporate Pch1, the gene for eyespot (Pseudocercosporella herpotrichoides) resistance on chromosome 7D, into commercial wheat. However, attempts to transfer resistance conferred by Pch2 (on chromosome 7A) through selection for Ep-A1b were not always successful. Linkage relations among eyespot resistance gene Pch2, a gene encoding for an isozyme of endopeptidase, Ep-A1b, and RFLP marker Xpsr121 on chromosome 7A were determined using 80 homozygous recombinant substitution lines. The recombinant lines were derived from eyespot susceptible cv. Chinese Spring hybridized with a resistant disomic substitution line of cv. Cappelle Desprez that has chromosome 7A substituted into Chinese Spring. Segregations of Pch2, Ep-A1b and Xpsr121 fit an expected 1 : 1 single-locus ratios based on chi2 tests. Linkage analysis revealed that Pch2 was not tightly linked to Ep-A1b (15% recombination). However, close linkage (3.8% recombination) existed between Ep-A1b and Xpsr121. The order of these loci is Pch2-Xpsr121-Ep-A1b. Unlike Pch1 and Ep-D1b, where little or no recombination is found, Pch2 and Ep-A1b showed considerable recombination and therefore linkage cannot be utilized efficiently in marker-based selection.
9. Registration of 'Madsen' wheat. Allan RE, Peteson CJ, Rubenthaler GL, Line RF, Roberst DE. In: Crop Science, 1989, 29:1575-1576.
10. Registration of 'Hyak' wheat. Allan RE, Peteson CJ, Rubenthaler GL, Line RF, Roberst DE. In: Crop Science, 1990, 30:234.
11. Amplified fragment length polymorphism-derived microsatellite sequence linked to the Pch1 and Ep-D1 loci in common wheat.. Groenewald JZ, Marais AS, Marais GF. In: Plant Breeding, 2003, 122: 83-85.
Amplified fragment length polymorphism (AFLP) markers linked to the Aegilops ventricosa-derived chromosome segment in 'VPM1' on which the eyespot resistance gene, Pch1, and the endopeptidase gene, Ep-D1b, occur were identified. One marker was isolated from the gel, cloned and sequenced. Sequence analysis revealed a microsatellite repeat motif. Sequence-specific primers were designed to amplify a product containing the repeat motif, and the microsatellite marker was tested for cosegregation with the Ep-D1b allele. Distinct alleles were produced by the Pch1 sources, normal wheat and wheat containing the Lr19 translocation. A recombination frequency of 0.02 was calculated between the microsatellite marker and Ep-D1.
12. Association of an isozyme locus and strawbreaker foot rot resistance derived from Aegilops ventricosa in wheat.. McMillian DE, Allan RE, Roberts DE. In: Theoretical and Applied Genetics, 1986, 72:743-747.