| There are three rust diseases that occur on wheat:stem rust, leaf rust and stripe rust. These diseases are each caused by a particular species of the "rust" fungus and can influence wheat production seriously. Puccinia striiformis f. sp. tritici (Pst) and Puccinia graminis f. sp. tritici (Pgt), the causal agent of wheat stripe rust and stem rust, has historically caused significant yield losses worldwide. Therefore, identification, mapping and deployment of effective resistance genes is the most economic, safe and effective way to control the disease. There are two objectives of this study:first, identification and mapping of stripe rust resistance genes in wheat germplasm D31 and HRMSN-81; second, fine mapping and characterization of the temperature-sensitive resistance gene Sr21 and the recessive broad-spectrum resistance gene SrTm4, both of which are from diploid wheat effective to Ug99. The main results are as follows:1. Characterization and mapping a stripe rust resistance gene YrSph in wheat lineD31 derived from Tritium sphaerococcum Perc.To determine inheritance of stripe rust resistance and map the resistance gene in a common wheat line D31, which developed from Triticum sphaerococcum Perc. (accession number AS348), we made a cross between D31 and Taichung 29. Then, the parents, F1, F2 and BC1 progenies derived from the Taichung 29XD31 cross were inoculated with Chinese PST race CYR32. SSR, SRAP and TRAP markers were used to map the resistance gene, we found:(1) The resistance to stripe rust in line D31 was controlled by a single recessive gene, temporarily designated as YrSph.(2) Four SSR markers, three SRAP markers and three TRAP markers were found to be linked to resistance gene. The markers Xwmc246 and F-me15/R-me6 flanked the locus at 8.5 and 6.9 cM, respectively.(3) The SSR markers mapped the resistance gene on chromosome arm 2AS.(4)The results of gene characteristics, pedigree analysis and chromosome location indicated that YrSph was probably a novel stripe rust resistance gene.2. Identification and mapping a stripe rust resistance gene YrHRMSN-81 in spring wheat germplasm HRMSN-81 from CIMMYTTo elucidate the genetic basis of stripe rust resistance and map the resistance gene in spring wheat germplasm HRMSN-81, the resistant parent HRMSN-81 was crossed with susceptible wheat genotype Taichung 29. The parents and F1, F2, and F23 progeny were inoculated with the epidemic Chinese PST isolates CYR31, CYR32, and CYR33. SSR, RGAP, SRAP and TRAP markers were used to identify molecular markers linked to the resistance gene, we found:(1) Genetic analysis showed that HRMSN-81 has a single dominant gene conferring all-stage resistance, temporarily designated as YrHRMSN-81.(2) Six RGAP, two SSR, one TRAP, and two SRAP markers were found to be linked to resistance gene, in which Xwgp-180bp was the nearest flanking marker with a genetic distance of 3.4 cM.(3) The gene was mapped to chromosome arm 2DS by testing the complete set of nulli-tetrasomic lines and selected ditelosomic lines with two RGAP markers. This result was further confirmed by two chromosome-specific SSR markers.(4) The results of gene characteristics and chromosome location indicated that YrHRMSN-81 was probably a new stripe rust resistance gene.3. Fine mapping Sr21, a temperature-sensitive diploid wheat resistance gene effective against the Puccinia graminis f. sp. tritici Ug99 race groupTo test the influence of different temperatures and photoperiods on gene Sr21, the T. monococcum genetic stock of Sr21 CI 2433 (PI 10474), Sr21 monogenic lines TD (T. monococcum derivative), T. monococcum deriv./8*LMPG and W3586, and susceptible checks Chinese Spring (CSA), LMPG-6, W2691 and PI 272557 were all inoculated with 16 Pgt isolates under three different temperatures and three different photoperiods (16℃/15h day,20℃/15h day,24℃/15h day,20℃/10h day and 20℃/20h day). Two big diploid wheat segregating populations used to map Sr21 resistance gene were derived from crosses between the susceptible T. monococcum PI 272557 and Ug99-resistant accessions DV92 and G3116. A total of 938 F2 plants in population PI 272557×DV92 and 2,850 plants in population PI 272557 × G3116 were used to fine mapping Sr21. Comparative genomics studies and different wheat databases were used in this study, we found:(1) The disease reaction between different isolates and Sr21 carrier lines is temperature sensitive. The difference in infection types from 16℃ to 20℃ (or 24℃) is obvious, representing a range between high infection types to low infection types, respectively.(2) We mapped 19 markers to Sr21 region by using two big populations (total 3,788 F2 plants). Sr21 was flanked by two CAP markers FD527726 and EX594406 with genetic distances of 0.15 cM and 0.05 cM, respectively.(3) The orthologs to wheat Sr21 flanking markers defined regions of 88 kb in Brachypodium chromosome 5 (Bd5:24573330bp-24661358bp) and 138 kb in rice chromosome 4 (Chr4:31527861bp-31665411bp). There are only 12 putative Brachypodium genes and 24 putative rice genes. These Brachypodium and rice genes included several typical resistance genes encoding NB-LRR domains.(4) We tested all the 12 putative Brachypodium genes, they are unlikely candidate genes for Sr21.4. Fine mapping SrTm4, a recessive stem rust resistance gene from diploid wheat effective to Ug99Two F2 mapping populations from the cross of PI 272557×PI 306540 and the cross of G3116 × PI 306540, were used to map SrTm4 in diploid wheat. A total of 89 F2 plants in population PI 272557 × PI 306540 and 2,192 plants in population G3116 × PI 306540 were used to fine mapping. F1, F2 and F2:3 progeny were inoculated with race TTTTF. Comparative genomics studies and different wheat databases were used in this study, we found:(1) T. monococcum accession PI 306540 contains a recessive resistance gene effective to all 10 Pgt races screened so far, which we will refer to as SrTm4.(2) We mapped 17 markers linked to SrTm4 by using two populations (total 2,281 F2 plants). SrTm4 was flanked by two CAP markers CD903048 and DR732348 with genetic distances of 0.05 cM and 0.16 cM, respectively.(3) The results of gene characteristics, the resistance spectrum analysis and chromosome locations indicated that SrTm4 and Sr21 are two different loci. For SrTm4 and Sr48, it is hard to distinguish them according to all the analyzes so far. So more work will need to be done to determine if SrTm4 and Sr48 are different genes.(4) The ortholog to wheat SrTm4 flanking markers defined a region of 54kb in Brachypodium chromosome 5 (Bd5:27074162bp-27127725bp). There are only 9 putative Brachypodium genes with no typical resistance genes encoding NB-LRR domains. |
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