Genes In Wheat Cultivars Research Articles

Development of wheat-tetraploid Thinopyrum elongatum 4EL small fragment translocation lines with stripe rust resistance gene Yr4EL.

Two small fragment translocation lines (T4DS·4DL-4EL and T5AS·5AL-4EL) showed high resistance to stripe rust and resistance gene Yr4EL was localized to an about 35 Mb region at the end of chr arm 4EL. Stripe rust, caused by the fungus Puccinia striiformis f. sp. tritici, is a devastating wheat disease worldwide. Deployment of disease resistance (R) genes in wheat cultivars is the most effective way to control the disease. Previously, the all-stage stripe rust R gene Yr4EL from tetraploid Thinopyrum elongatum was introduced into common wheat as 4E(4D) substitution and T4DS·4EL translocation lines. To further map and utilize Yr4EL, Chinese Spring (CS) mutant pairing homoeologous gene ph1b was used in crossing to induce recombination between chromosome (chr) 4EL and wheat chromosomes. Two small fragment translocation lines T4DS·4DL-4EL and T5AS·5AL-4EL with Yr4EL resistance were selected using molecular markers and confirmed by genomic in situ hybridization (GISH), fluorescence in situ hybridization (FISH), and Wheat660K SNP array analyses. We mapped Yr4EL to an about 35Mb region at the end of chr 4EL, corresponding to 577.76-612.97Mb based on the diploid Th. elongatum reference genome. In addition, two competitive allele-specific PCR (KASP) markers co-segregating with Yr4EL were developed to facilitate molecular marker-assisted selection in breeding. The T4DS·4DL-4EL lines were crossed and backcrossed with wheat cultivars SM482 and CM42, and the resulting pre-breeding lines showed high stripe rust resistance and potential for wheat breeding with good agronomic traits. These lines represent new germplasm for wheat stripe rust resistance breeding, as well as providing a solid foundation for Yr4EL fine mapping and cloning.

Identification and Screening of Leaf Rust Resistance Genes in Wheat Cultivars Through Microsatellites

Wheat is one of the important staple food being grown worldwide and in Pakistan. The wheat rust-causing fungi are very eco-adaptive and evolve rapidly to overcome genetic resistance of wheat varieties. Among all rust-causing fungi, Puccinia triticina causes leaf rust in wheat, and inflicts heavy yield losses. Deploying resistant varieties against leaf rust is the most effective, environmentally-friendly and economic way to control the disease. Therefore, new sources of genetic resistance are continually sought to develop rust resistance in wheat varieties, and nowadays rust resistant varieties have been developed through the accumulation of slow rusting or minor genes that would perform better in fields. Hence, the purpose of this study is to screen a few of the available leaf rust-resistant germplasm in field and evaluate their field response on genetic basis. For this purpose, minor genes were detected through the amplification of simple sequence repeat (SSR) in the selected wheat genotypes through screened primers. Field experiment was conducted. Molecular studies to identify the minor genes were performed. Meteorological data was recorded at the observatory laboratory of the same area. All the epidemiological factors (Temperature (maximum, minimum), Relative Humidity, and Pan Evaporation) showed significant correlation in tested 5 varieties ZARDANA89, ZARLASHTA99, RASKOH 05, BHAKKAR-2000, GA-2002 which were conducive for disease development except rainfall. PCR amplification of Xgwm118, and Xgwm165, showed the range of alleles in 14 genotypes. It was observed that 22 verities showed resistance, 3 were moderately resistant, 3 varieties were moderately susceptible, 8 varieties were moderately susceptible, and 5 varieties were moderately susceptible against leaf rust pathogen.

Allelic variation and effects of earliness <i> per se (Eps) </i> genes in wheat cultivars of Pakistan

Optimization of the flowering time in wheat is an important breeding target for its adaptability in target environments. Flowering time is controlled by vernalization, photoperiod, and the relatively poorly characterized earliness per se (Eps) genes. When vernalization and photoperiod criteria are met, Eps genes account for the variance in flowering time. The objective of the study was to decipher the allelic variations for Eps genes in the wheat cultivars of Pakistan and draw their association with agronomic traits. The wheat cultivars released prior to 1965 had an average flowering duration of 82 days, whereas the cultivars released between 1965 and 2000 had an average flowering time of 79 days and 81 days, respectively. Kompetitive allele-specific PCR (KASP) markers were used to genotype all these cultivars for TaElf3-B1, TaElf3-D1, and TaMOT1-D1 genes. For the gene TaElf3-B1, allele Cadenza-type had a frequency of 61.71%. For the gene TaElf3-D1, the proportion of its respective major alleles was recorded, i.e., deletion had a frequency of 72.94%, and Savannah-type was 86.04%. For the gene TaMOT1-D1, the allele Wild-type was found in 55.88% accessions. The gene Elf3-B1 had a significant allelic effect for grain yield (GY), TaElf3-D1 for grain length, and TaMOT1-D1 for GY. Among the wheat cultivars, high percentage (56.89%) of the Savanah-type allele was associated with early flowering. However, the Wild-type alleles (43.1%) were observed to have low allelic frequency, and they were associated with late flowering. This study may allow wheat breeders to make genetic selection of wheat cultivars that are most suited to target environment, ensuring better yield and adaptability.

Identification of wheat stem rust resistance genes in wheat cultivars from Hebei province, China.

Wheat stem rust is caused by Puccinia graminis f. sp. tritici. This major disease has been effectively controlled via resistance genes since the 1970s. The appearance and spread of new races of P. graminis f. sp. tritici (eg., Ug99, TKTTF, and TTRTF) have renewed the interest in identifying the resistance gene and breeding cultivars resistant to wheat stem rust. In this study, gene postulation, pedigree analysis, and molecular detection were used to determine the presence of stem rust resistance genes in 65 commercial wheat cultivars from Hebei Province. In addition, two predominant races 21C3CTHTM and 34MRGQM were used to evaluate the resistance of these cultivars at the adult-plant stage in 2021-2022. The results revealed that 6 Sr genes (namely, Sr5, Sr17, Sr24, Sr31, Sr32, Sr38, and SrTmp), either singly or in combination, were identified in 46 wheat cultivars. Overall, 37 wheat cultivars contained Sr31. Sr5 and Sr17 were present in 3 and 3 cultivars, respectively. Gao 5218 strong gluten, Jie 13-Ji 7369, and Kenong 1006 contained Sr24, Sr32, and Sr38, respectively. No wheat cultivar contained Sr25 and Sr26. In total, 50 (76.9%) wheat cultivars were resistant to all tested races of P. graminis f. sp. tritici in field test in 2021-2022. This study is important for breeding wheat cultivars with resistance to stem rust.

Leaf rust (Puccinia triticina Eriks) resistance genes in wheat cultivars registered in the Czech Republic

Leaf rust (Puccinia triticina Eriks) resistance genes in wheat cultivars registered in the Czech Republic

Phenotyping and validation of molecular markers associated with rust resistance genes in wheat cultivars in Egypt.

Thirteen Egyptian wheat cultivars were evaluated and characterized for adult plant resistance to yellow, leaf, and stem rusts. SSR markers linked to yellow, leaf and stem rust resistance genes were validated and subsequently used to identify wheat cultivars containing more than one rust resistance gene. Results of the molecular marker detection indicated that several genes, either alone or in different combinations, were present among the wheat cultivars, including Yr, Yr78 (stripe rust), Lr, Lr70 (leaf rust), Sr. Sr33, SrTA10187, Sr13, and Sr35 (stem rust), and Lr34/Yr18 and Lr49/Yr29 (leaf/stripe rust). The cultivar Sakha-95 was resistant to leaf and stem rusts, and partially resistant to stripe rust; however, this cultivar contained additional rust resistance genes (Lr, Sr and Lr/Yr). The area under the disease progress curve (AUDPC) type for the various wheat cultivars differed depending on the type of rust infection (yellow, leaf, or stem rust, indicated by Yr, Lr, and Sr). The cultivars Gem-12, Sids-14, Giza-171, and Giza-168 had AUDPC types of partial resistance and resistance. All six cultivars, however, contained additional rust resistance genes. Marker-assisted selection can be applied to improve wheat cultivars with efficient gene combinations that would directly support the development of durable resistance in Egypt. Once the expression of the resistance genes targeted in this study have been confirmed by phenotypic screening, the preferable cultivars can be used as donors by Egyptian wheat breeders. The results of this study will help breeders determine the extent of resistance under field conditions when breeding for rust resistance in bread wheat.

The Emergence of New Aggressive Leaf Rust Races with the Potential to Supplant the Resistance of Wheat Cultivars.

Simple SummaryThe pathogen that causes wheat leaf rust, Puccinia triticina, possesses numerous aggressive races that can erode the resistant genes in its host. This study presents the recognition of the new physiological races of P. triticina, their distribution, and their resistance genes in wheat cultivars, which are critical for directing and improving wheat breeding programs for resistance to leaf rust. Winds often transport the pathogen’s initial inoculum from one country to another. Our findings trigger an alert to the whole world about developing races capable of supplanting leaf rust resistance.Characterization of the genetic structure and the physiological races of Puccinia triticina is a growing necessity to apply host genetic resistance against wheat leaf rust as a successful control strategy. Herein, we collected and identified about 130 isolates of P. triticina from 16 Egyptian commercial wheat cultivars grown at different locations, over two seasons (2019/2020 and 2020/2021). The 130 isolates of P. triticina were segregated into 17 different physiological races. TTTST and TTTKS were the most common virulent races, whereas TTTST and MTTGT were the most frequent races. The races were classified into three groups, based on their distinct DNA band sizes (150 bp, 200 bp, and 300 bp) after RAPD analysis. The new wheat cultivars (Sakha-94, Sakha-95, and Shandweel-1) infected with the most virulent race (TTTST), Gemmeiza-12, and Misr-3 were resistant to all physiological races. The resistance of these cultivars was mostly due to the presence of Lr19- and Lr28-resistant genes. Our results serve as a warning about emerging aggressive races capable of supplanting resistance to leaf rust, and help in the understanding of the pathotype–cultivar–location association and its role in the susceptibility/resistance of new wheat cultivars to P. triticina.

Virulence of wheat leaf rust (Puccinia triticina Eriks.) and Lr resistance genes in wheat cultivars in the Slovak Republic in the years 2016–2019

In the years 2016 to 2019 the virulence of the wheat leaf rust population in Slovakia was tested on Thatcher near-isogenic lines Lr1, Lr2a, Lr2b, Lr2c, Lr3a, Lr9, Lr10, Lr11, Lr13, Lr15, Lr17a, Lr19, Lr21, Lr23, Lr24, Lr26 and Lr28. A total of 111 rust isolates were analysed. Resistance genes Lr19 and Lr9 were effective to most of the tested isolates. Average virulence frequency to these resistance genes was only 1%. The gene Lr24 conditioned resistance to 92% of the tested rust isolates, gene Lr28 to 86% of the tested rust isolates. Low virulence frequency was also recorded to Lr2a (13%), Lr2b and Lr2c (both 12%). Average virulence to other tested Lr genes exceeded 82%. Thirty-eight winter wheat cultivars registered in the Slovak Republic were tested for the presence of Lr10, Lr19, Lr24, Lr26, Lr28, Lr34 and Lr37 by molecular markers. The gene Lr34 was the most frequent one in the tested cultivars, followed by Lr37 (both genes for adult plant resistance). The most widespread pathotypes in separate years and leaf rust severity in thirty-eight cultivars are also recorded.

Leaf Rust Resistance Genes in Wheat Cultivars Registered in Russia and Their Influence on Adaptation Processes in Pathogen Populations

The main growing regions for winter wheat in the Russian Federation are the North Caucasian, Central Black Earth, and Central agroecological regions. Spring wheat crops dominate in the Urals, Volga region, and Western Siberia. Wheat leaf rust, caused by Puccinia triticina, is an important disease, impacting greatly on wheat production. In Russia, the disease was an annual problem until 2010 but has since been more effectively controlled. However, changes in virulence in pathogen populations may arise from climate change, evolving cropping practices, intense use of chemical protectants, and an increase in the release of resistant cultivars. In the 2000s, the State Register of the Russian Federation included an increase in the number of winter and spring wheat cultivars resistant to leaf rust. However, successful genetic protection requires a diversity of cultivars with different resistance genes (Lr genes). Studies by the All Russian Institute of Plant Protection identified Lr genes in Russian cultivars’ phenotypes and molecular markers. In addition, the prevalence of virulence in pathogen populations was studied and the influence of the cultivar used in wheat production on the changes in these populations was evaluated. This paper reviews research on the genetic diversity of winter and spring wheat cultivars included in the State Register of Russia from 2000 to 2020 and analyzes their impact on the prevalence of virulence in pathogen populations. These data demonstrate the continuous evolution of P. triticina in response to wheat breeding efforts. Populations of the pathogen showed higher variability in regions where pathotype-specific resistance cultivars were commonly grown.

Evaluation of resistance to powdery mildew and identification of resistance genes in wheat cultivars.

Wheat powdery mildew, caused by the biotrophic fungus Blumeria graminis f. sp. tritici (Bgt), is a serious disease of wheat worldwide that can cause significant yield losses. Growing resistant cultivars is the most cost-effective and eco-soundly strategy to manage the disease. Therefore, a high breeding priority is to identify genes that can be readily used either singly or in combination for effective resistance to powdery mildew and also in combination with genes for resistance to other diseases. Yunnan Province, with complex and diverse ecological environments and climates, is one of the main wheat growing regions in China. This region provides initial inoculum for starting epidemics of wheat powdery mildew in the region and other regions and thus, plays a key role in the regional and large-scale epidemics of the disease throughout China. The objectives of this study were to evaluate seedling resistance of 69 main wheat cultivars to powdery mildew and to determine the presence of resistance genes Pm3, Pm8, Pm13, Pm16, and Pm21in these cultivars using gene specific DNA markers. Evaluation of 69 wheat cultivars with six Bgt isolates showed that only four cultivars were resistant to all tested isolates, indicating that the overall level of powdery mildew resistance of Yunnan wheat cultivars is inadequate. The molecular marker results showed that 27 cultivars likely have at least one of these genes. Six cultivars were found likely to have Pm3,18 likely to have Pm8,5 likely to have Pm16,and 3 likely to have Pm21. No cultivar was found to carry Pm13. The information on the presence of the Pmresistance genes in Yunnan wheat cultivars can be used in future wheat disease breeding programs. In particular, cultivars carrying Pm21, which is effective against all Bgtraces in China, should be pyramided with other effective genes to developing new cultivars with durable resistance to powdery mildew.

Wheat leaf rust (Puccinia triticina Eriks.) virulence frequency and detection of resistance genes in wheat cultivars registered in the Czech Republic in 2016-2018

In 2016–2018 virulence of the Czech wheat leaf rust population was studied on Thatcher near-isogenic lines, carrying different Lr genes, and 130 leaf rust isolates. Virulence to Lr9 was found only sporadically. Virulence frequency to Lr2a, Lr2b, Lr2c and Lr28 was lower than in previous years. All tested isolates were avirulent to Lr19. Lr24 conditioned resistance to majority of isolates. Nineteen recently registered Czech cultivars were tested with six isolates of the pathogen and Lr genes were postulated. Presence of genes Lr1, Lr10, Lr19, Lr24, Lr26, Lr28, Lr34 and Lr37 was tested by molecular markers. Lr37 prevailed, followed by Lr genes 10, 24, 28, 1 and 26; genes Lr19 and Lr34 were not determined.

Introgression of Two Quantitative Trait Loci for Stripe Rust Resistance into Three Chinese Wheat Cultivars

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most devastating diseases in wheat. Due to the large-scale and widely-distributed planting pattern of wheat, the directional selection pressure of the pathogen is very strong. Therefore, it is urgent to pyramid more stripe rust resistance genes in wheat cultivars to enhance resistance durability and ensure wheat production safety. In this study, two quantitative trait loci (QTL) for adult plant resistance (APR) to stripe rust, QYr.nafu-2BL and QYr.nafu-3BS, were validated and introgressed from wheat line P9897 into three Chinese elite wheat cultivars, Chuanmai 42, Xiangmai 25, and Zhengmai 9023, through marker validation. The three Chinese elite varieties were used as the female parent to cross with wheat line P9897, and they were selfed to the F6 generation. A total of 114 lines were then selected based on field agronomic traits and stripe rust resistance. Four markers (Xcfd73, Xgwm120, Xbarc87 and Xbarc133) linked with the QTL’s regions were employed to screen the 114 F6 lines. Subsequently, 27 lines combining two target QTL from P9897 were selected. The combination of agronomic traits and disease resistance results showed that 13 of these selected lines had favorable application prospects. The promising lines selected in this study could enrich the genetic resources of wheat stripe rust resistance genes, as well as provide material support and a theoretical basis for the prevention and control of wheat stripe rust in China.

Endemic and panglobal genetic groups, and divergence of host-associated forms in worldwide collections of the wheat leaf rust fungus Puccinia triticina as determined by genotyping by sequencing.

The wheat leaf rust fungus, Puccinia triticina, is found in the major wheat growing regions of the world and is a leading cause of yield loss in wheat. Populations of P. triticina are highly variable for virulence to resistance genes in wheat and adapt quickly to resistance genes in wheat cultivars. The objectives of this study were to determine the genetic relatedness of worldwide collections of P. triticina using restriction site associated genotyping by sequencing. A total of 558 isolates of P. triticina from wheat producing regions in North America, South America, Europe, the Middle East, Ethiopia, Russia, Pakistan, Central Asia, China, New Zealand, and South Africa were characterized at 6745 single nucleotide loci. Isolates were also tested for virulence to 20 near-isogenic lines that differ for leaf rust resistance genes. Populations that were geographically proximal were also more closely related for genotypes. In addition, groups of isolates within regions that varied for genotype were similar to groups from other regions, which indicated past and recent migration across regions. Isolates from tetraploid durum wheat in five different regions were highly related with distinct genotypes compared to isolates from hexaploid common wheat. Based on a molecular clock, isolates from durum wheat found only in Ethiopia were the first to diverge from a common ancestor form of P. triticina that is found on the wild wheat relative Aegilops speltoides, followed by the divergence of isolates found worldwide that are virulent to durum wheat, and then by isolates found on common wheat.

Identification of stem rust resistance genes in wheat cultivars in China using molecular markers.

Wheat stem rust caused by Puccinia graminis f. sp. tritici Eriks. & E. Henn. (Pgt), is a major disease that has been effectively controlled using resistance genes. The appearance and spread of Pgt races such as Ug99, TKTTF, and TTTTF, which are virulent to most stem rust-resistant genes currently deployed in wheat breeding programs, renewed the interest in breeding cultivars resistant to wheat stem rust. It is therefore important to investigate the levels of resistance or vulnerability of wheat cultivars to Pgt races. Resistance to Pgt races 21C3CTHQM, 34MKGQM, and 34C3RTGQM was evaluated in 136 Chinese wheat cultivars at the seedling stage. A total of 124 cultivars (91.2%) were resistant to the three races. Resistance genes Sr2, Sr24, Sr25, Sr26, Sr31, and Sr38 were analyzed using molecular markers closely linked to them, and 63 of the 136 wheat cultivars carried at least one of these genes: 21, 25, and 28 wheat cultivars likely carried Sr2, Sr31, and Sr38, respectively. Cultivars “Kehan 3” and “Jimai 22” likely carried Sr25. None of the cultivars carried Sr24 or Sr26. These cultivars with known stem rust resistance genes provide valuable genetic material for breeding resistant wheat cultivars.

Seedling Resistance to Stem Rust (<i>Puccinia graminis</i> f.sp.<i>tritici</i>) and Molecular Marker Analysis of Resistance Genes in Some Wheat Cultivars

Stem rust caused by Puccinia graminis Pers.f.sp.<i>tritici</i> Eriks.and E.Henn.(Pgt) is one of the most destructive diseases of wheat which causing considerable yield losses in wheat growing areas worldwide. It has become a renewed threat to global wheat production after the emergence and spread of race TTKSK (also known as Ug99) and related races from Africa. Races of the pathogen in the “Ug99 lineages” are of international concern due to their virulence for widely used stem rust resistance genes and their spread throughout Africa. Disease resistant cultivars provide one of the best means for controlling stem rust. Bale zone, located on the Southeast part of Ethiopia, is one of the main wheat growing regions, playing a pivotal role in the wheat stem rust epidemic in Ethiopia. This study investigated levels of resistance in key wheat cultivars (lines) grown in Bale zone using seedling resistance evaluation and marker aided selection. Twenty wheat cultivars were evaluated for their response to stem rust infection at seedling stage under green house condition. Wheat cultivars were challenged with four stem rust races <i>viz</i> TTKSK, TRTTF, TTTTF and JRQCQ. A high level of phenotypic variation was observed in response to these races in the test entries, allowing for selection in these germplasm as a pre-breeding work. Out of the tested cultivars, three wheat cultivars exhibited low infection types (0–2) response to all the four races and hence selected as a source of resistance to stem rust. In addition, the existence of <i>Sr2, Sr22, Sr24, Sr25, Sr26, Sr35</i> and Sr36 genes in wheat cultivars were assessed using specific DNA markers. Using molecular markers, resistance gene Sr2 was identified in 2 cultivars and <i>Sr24</i> in five cultivars. However, no <i>Sr25, Sr26, Sr35</i> and <i>Sr36</i> were identified in any cultivars tested using DNA markers. The results of both seedling evaluation and marker based resistance gene identification will enable to breed wheat varieties with durable resistance to stem rust disease.

Evaluation and identification of stem rust resistance genes Sr2, Sr24, Sr25, Sr26, Sr31 and Sr38 in wheat lines from Gansu Province in China.

Wheat stem rust, caused by Puccinia granimis f. sp. tritici, severely affects wheat production, but it has been effectively controlled in China since the 1970s. However, the appearance and spread of wheat stem rust races Ug99 (TTKSK, virulence to Sr31), TKTTF (virulence to SrTmp) and TTTTF (virulence to the cultivars carrying Sr9e and Sr13) have received attention. It is important to clarify the effectiveness of resistance genes in a timely manner, especially for the purpose of using new resistance genes in wheat cultivars for durable-resistance. However, little is known about the stem rust resistance genes present in widely used wheat cultivars from Gansu. This study aimed to determine the resistance level at the seedling stage of the main wheat cultivars in Gansu Province. A secondary objective was to assess the prevalence of Sr2, Sr24, Sr25, Sr26, Sr31, and Sr38 using molecular markers. The results of the present study indicated that 38 (50.7%) wheat varieties displayed resistance to all the tested races of Puccinia graminis f. sp. tritici. The molecular marker analysis showed that 13 out of 75 major wheat cultivars likely carried Sr2; 25 wheat cultivars likely carried Sr31; and nine wheat cultivars likely carried Sr38. No cultivar was found to have Sr25 and Sr26, as expected. Surprisingly, no wheat cultivars carried Sr24. The wheat lines with known stem rust resistance genes could be used as donor parent for further breeding programs.

A Novel, Economical Way to Assess Virulence in Field Populations of Hessian Fly (Diptera: Cecidomyiidae) Utilizing Wheat Resistance Gene H13 as a Model.

Mayetiola destructor (Say) is a serious pest of wheat, Triticum aestivum L., in North America, North Africa, and Central Asia. Singly deployed resistance genes in wheat cultivars have provided effective management of Hessian fly populations for >50 yr. Thirty-five H genes have been documented. Defense mediated by the H gene constitutes strong selection on the Hessian fly population, killing 100% of larvae. A mutation in a matching Hessian fly avirulence gene confers virulence to the H gene, leading to survival on the resistant plant. As the frequency of virulence rises in the population, the H gene loses its effectiveness for pest management. Knowing the frequency of virulence in the population is not only important for monitoring but also for decisions about which H gene should be deployed in regional wheat breeding programs. Here, we present a novel assay for detecting virulence in the field. Hessian fly males were collected in Alabama, Georgia, North Carolina, and South Carolina using sticky traps baited with Hessian fly sex pheromone. Utilizing two PCR reactions, diagnostic molecular markers for the six alleles controlling avirulence and virulence to H13 can be scored based on band size. Throughout the southeast, all three avirulence and three virulence alleles can be identified. In South Carolina, the PCR assay was sensitive enough to detect the spread of virulence into two counties previously documented as 100% susceptible to H13. The new assay also indicates that the previous methods overestimated virulence in the field owing to scoring of the plant instead of the insect.

Expression of the aldehyde oxidase 3, ent-copalyl diphosphate synthase, and VIVIPAROUS 1 genes in wheat cultivars differing in their susceptibility to pre-harvest sprouting

The quality of wheat grains is often negatively affected by pre-harvest sprouting (PHS), a complex trait with a poorly understood genetic background. In this study two wheat cultivars differing in their susceptibility to PHS were used to investigate expression of three genes: AAO3, CPS3 and VP1. AAO3 is coding for aldehyde oxidase 3, an enzyme involved in the synthesis of abscisic acid. CPS3 codes for ent-copalyl diphosphate synthase which belongs to the pathway of gibberellic acid synthesis. The product of VP1 (VIVIPAROUS 1) is a transcription factor which controls expression of the former two genes. The study was carried out using both developing and sprouting-induced grains. In Piko, a wheat cultivar susceptible to PHS, accumulation of the AAO3 transcript was significantly decreased, during the last stages of grain development, in comparison to Sława, a cultivar tolerant to PHS. In case of the CPS3 and VP1 transcripts, the differences between cultivars were especially evident from 17th to 31st day after pollination. In turn, after induction of sprouting within spikes, accumulation of the AAO3 and VP1 mRNA in the Sława grains was lower in comparison to that observed in the Piko grains. Moreover, accumulation of the CPS3 transcript was significantly higher for Piko than for Sława, both in sprouting and non-sprouting grains. According to our knowledge this report provides the first description of the AAO3 and CPS3 expression in the context of PHS, and in the future it would be valuable to correlate this information with the data on the accumulation of ABA and GA3.

Fine mapping of powdery mildew resistance gene PmTm4 in wheat using comparative genomics

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is one of the most severe wheat diseases. Mining powdery mildew resistance genes in wheat cultivars and their appliance in breeding program is a promising way to control this disease. Genetic analysis revealed that a single dominant resistance gene named PmTm4 originated from Chinese wheat line Tangmai 4 confers resistance to prevailing isolates of B. graminis f. sp. tritici isolate E09. Detailed comparative genomics analyses helped to develop closely linked markers to PmTm4 and a fine genetic map was constructed using large F2 population, in which PmTm4 was located into a 0.66-cM genetic interval. The orthologous subgenome region of PmTm4 in Aegilops tauschii was identified, and two resistance gene analogs (RGA) were characterized from the corresponding sequence scaffolds of Ae. tauschii draft assembly. The closely linked markers and identified Ae. tauschii orthologs in the mapping interval provide an entry point for chromosome landing and map-based cloning of PmTm4.

Seedling Resistance to Stem Rust and Molecular Marker Analysis of Resistance Genes in Wheat Cultivars of Yunnan, China.

Stem rust is one of the most potentially harmful wheat diseases, but has been effectively controlled in China since 1970s. However, the interest in breeding wheat with durable resistance to stem rust has been renewed with the emergence of Ug99 (TTKSK) virulent to the widely used resistance gene Sr31, and by which the wheat stem rust was controlled for 40 years in wheat production area worldwide. Yunnan Province, located on the Southwest border of China, is one of the main wheat growing regions, playing a pivotal role in the wheat stem rust epidemic in China. This study investigated the levels of resistance in key wheat cultivars (lines) of Yunnan Province. In addition, the existence of Sr25, Sr26, Sr28, Sr31, Sr32, and Sr38 genes in 119 wheat cultivars was assessed using specific DNA markers. The results indicated that 77 (64.7%) tested wheat varieties showed different levels of resistance to all the tested races of Puccinia graminis f. sp. tritici. Using molecular markers, we identified the resistance gene Sr31 in 43 samples; Sr38 in 10 samples; Sr28 in 12 samples, and one sample which was resistant against Ug99 (avirulent to Sr32). No Sr25 or Sr26 (effective against Ug99) was identified in any cultivars tested. Furthermore, 5 out of 119 cultivars tested carried both Sr31 and Sr38 and eight contained both Sr31 and Sr28. The results enable the development of appropriate strategies to breed varieties resistant to stem rust.