Resistant Wheat Cultivars Research Articles

New insights in the battle between wheat and Puccinia striiformis

Wheat stripe rust caused by Puccinia striifor- mis f. sp. tritici (Pst) poses a great threat to wheat production worldwide. The rapid change in virulence of Pst leads to a loss of resistance in currently resistant wheat cultivars, which results in frequent disease epidemics. Therefore, a major focus is currently placed on investigating the molecular mechanisms underlying this rapid variation of pathogenicity and coevolving wheat resistance. Limited by the lack of a system for stable transformation of Pst and the difficulties in wheat transformation, it is not easy to generate deeper insights into the wheat-Pst interaction using established genetic methods. Nevertheless, considerable effort has been made to unravel the wheat-Pst interaction and significant progress is being made. Histology and cytology have revealed basic details of infection strategies and defense responses during wheat-Pst interactions, identified cellular components involved in wheat-Pst interactions, and have helped to elucidate their role in the infection process or in plant defense responses. Transcriptome and genome sequencing has revealed the molecular features and dynamics of the wheat-Pst pathosystem. Extensive molecular analyses have led to the identification of major components in the wheat resistance response and in Pst virulence. Studies of wheat-Pst interactions have now entered a new phase in which cellular and molecular approaches are being used. This review focuses on the cellular biology of wheat-Pst interactions and integrates the emerging data from molecular analyses with the histocytological observations.

Identification of a wheat polygalacturonase-inhibiting protein involved in Fusarium head blight resistance

The plant cell wall is the first barrier to obstruct attack by pathogens. The polygalacturonase-inhibiting protein (PGIP) can specifically recognize and inhibit polygalacturonase (PG), a hydrolase that is secreted by fungi to invade plants, thus protecting plants from fungal infection by reducing the hydrolytic activity of PGs. In this study, we cloned a novel PGIP gene, Tapgip3, that is located on the 7D chromosome and encoded a 791 amino acid protein in the Fusarium head blight (FHB)-resistant wheat cultivar Ning7840. The real-time PCR analysis showed that this gene was upregulated sharply in spikes at 48 h after infection by either Fusarium graminearum or the trichothecene deoxynivalenol (DON). Subcellular localization analysis revealed that TaPGIP3 was secreted on the plant cell wall. When the transcripts of Tapgip3 were knocked down by barley stripe mosaic virus—virus-induced gene silencing (BSMV-VIGS), the growth of F. graminearum hyphae was promoted with larger lesions on wheat leaves. This suggests that Tapgip3 plays an important role in the response to F. graminearum infection. Although salicylic acid (SA), methyl jasmonate (MeJA) and abscisic acid (ABA) have been reported to be involved in wheat FHB resistance, we demonstrate in our study that the two copies of Tapgip3 are negatively regulated by these three hormones and positively regulated by indoleacetic acid (IAA).

GmPGIP3 enhanced resistance to both take-all and common root rot diseases in transgenic wheat.

Take-all (caused by the fungal pathogen Gaeumannomyces graminis var. tritici, Ggt) and common root rot (caused by Bipolaris sorokiniana) are devastating root diseases of wheat (Triticum aestivum L.). Development of resistant wheat cultivars has been a challenge since no resistant wheat accession is available. GmPGIP3, one member of polygalacturonase-inhibiting protein (PGIP) family in soybean (Glycine max), exhibited inhibition activity against fungal endopolygalacturonases (PGs) in vitro. In this study, the GmPGIP3 transgenic wheat plants were generated and used to assess the effectiveness of GmPGIP3 in protecting wheat from the infection of Ggt and B. sorokiniana. Four independent transgenic lines were identified by genomic PCR, Southern blot, and reverse transcription PCR (RT-PCR). The introduced GmPGIP3 was integrated into the genomes of these transgenic lines and could be expressed. The expressing GmPGIP3 protein in these transgenic wheat lines could inhibit the PGs produced by Ggt and B. sorokiniana. The disease response assessments postinoculation showed that the GmPGIP3-expressing transgenic wheat lines displayed significantly enhanced resistance to both take-all and common root rot diseases caused by the infection of Ggt and B. sorokiniana. These data suggested that GmPGIP3 is an attractive gene resource in improving resistance to both take-all and common root rot diseases in wheat.

Leaf and stem seedling rust resistance in wheat cultivars grown in Croatia

Diseases caused by Puccinia species can have devastating effects on wheat and other crops, causing severe economic losses by reducing grain yield and quality. Generally, three strategies are used to control leaf and stem rust wheat diseases: (i) incorporating genetic resistance into new cultivars (ii) the use of fungicides (iii) crop management. The first approach is the most environmentally and economically efficient. Combined with traditional selection techniques, marker-assisted selection (MAS) has become a valuable tool in selection of individuals carrying genes that control traits of interest, such as disease resistance. The objective of this study is to postulate leaf and stem rust resistance genes in 50 mostly Croatian wheat cultivars. Most of the cultivars were screened for the first time for rust diseases. The studies detected six leaf rust resistance genes (Lr2a, Lr3, Lr10, Lr14a, Lr17 and Lr26) and four stem leaf resistance genes (Sr8a, Sr31, Sr36 and Sr38). Nine wheat cultivars had one or more unidentified Lr genes that were not included in the set of 24 isolines, and six wheat cultivars had one or more unidentifed Sr genes. Knowledge on the identity of the seedling rust resistance genes in released cultivars and germplasm is essential for the incorporation of effective resistance genes into breeding programs to maintain a diversity of resistance genes in commonly grown cultivars.

Development of IRAP- and REMAP-derived SCAR markers for marker-assisted selection of the stripe rust resistance gene Yr15 derived from wild emmer wheat.

Yr15 provides broad resistance to stripe rust, an important wheat disease. REMAP- and IRAP-derived co-dominant SCAR markers were developed and localize Yr15 to a 1.2 cM interval. They are reliable across many cultivars. Stripe rust [Pucinia striiformis f.sp. tritici (Pst)] is one of the most important fungal diseases of wheat, found on all continents and in over 60 countries. Wild emmer wheat (Triticum dicoccoides), which is the tetraploid progenitor of durum wheat, is a valuable source of novel stripe rust resistance genes for wheat breeding. T. dicoccoides accession G25 carries Yr15 on chromosome 1BS. Yr15 confers resistance to virtually all tested Pst isolates; it is effective in durum and bread wheat introgressions and their derivatives. Retrotransposons generate polymorphic insertions, which can be scored as Mendelian markers using techniques such as REMAP and IRAP. Six REMAP- and IRAP-derived SCAR markers were mapped using 1,256 F2 plants derived from crosses of the susceptible T. durum accession D447 (DW1) with its resistant BC3F9 and BC3F10 (B9 and B10) near isogenic lines, which carried Yr15 introgressed from G25. The nearest markers segregated 0.1 cM proximally and 1.1 cM distally to Yr15. These markers were also mapped and validated at the same position in another 500 independent F2 plants derived from crosses of B9 and B10 with the susceptible cultivar Langdon (LDN). SC2700 and SC790, defining Yr15 on an interval of 1.2 cM, were found to be reliable and robust co-dominant markers in a wide range of wheat lines and cultivars with and without Yr15. These markers are useful tags in marker-assisted wheat breeding programs that aim to incorporate Yr15 into elite wheat lines and cultivars for durable and broad-spectrum resistance to stripe rust.

Evaluation of wheat cultivars for slow rusting resistance in Guji zone, Southern Oromia

Evaluation of Eleven and local bread wheat cultivars evaluated for slow rusting resistance was conducted in Bore district of southern Oromia during the main cropping season of 2011 under natural epidemics at Bore Agricultural Research site. Field evaluation of slow rusting resistance was assessed through Incidence, disease severity (DS), AUDPC and rAUDPC. Results of mean comparison of final rust severity, AUDPC and rAUDPC indicating that the cultivars; PBW343, Kubsa, Hawi, local and Galema had highest final rust severity (FRS) and rAUDPC and susceptible infection (4) at the later growth stage. Shorima, Danda`a, Kakaba, ET13A2 and Digalu had moderately resistance to moderately susceptible infection type at later growth stage. However, disease development on this cultivar was very slow compared to the highly susceptible cultivars. That why these cultivars had low disease severity, low AUDPC and rAUDPC, that is, up to 70% of susceptible cultivars and they could have probably slow rusting resistance. Cultivar ETBW5496 had no any infection and thus selected as immune or resistance cultivar. Key words: Slow rusting, rAUDPC, Oromia.

Dynamics of small RNA profiles of virus and host origin in wheat cultivars synergistically infected by Wheat streak mosaic virus and Triticum mosaic virus: virus infection caused a drastic shift in the endogenous small RNA profile.

Co-infection of wheat (Triticum aestivum L.) by Wheat streak mosaic virus (WSMV, a Tritimovirus) and Triticum mosaic virus (TriMV, a Poacevirus) of the family Potyviridae causes synergistic interaction. In this study, the effects of the synergistic interaction between WSMV and TriMV on endogenous and virus-derived small interfering RNAs (vsiRNAs) were examined in susceptible (‘Arapahoe’) and temperature-sensitive resistant (‘Mace’) wheat cultivars at 18°C and 27°C. Single and double infections in wheat caused a shift in the profile of endogenous small RNAs from 24 nt being the most predominant in healthy plants to 21 nt in infected wheat. Massive amounts of 21 and 22 nt vsiRNAs accumulated in singly and doubly infected Arapahoe at both temperatures and in Mace at 27°C but not 18°C. The plus- and minus-sense vsiRNAs were distributed throughout the genomic RNAs in Arapahoe at both temperature regimens and in Mace at 27°C, although some regions served as hot-spots, spawning an excessive number of vsiRNAs. The vsiRNA peaks were conserved among cultivars, suggesting that the Dicer-like enzymes in susceptible and resistant cultivars similarly accessed the genomic RNAs of WSMV or TriMV. Accumulation of large amounts of vsiRNAs in doubly infected plants suggests that the silencing suppressor proteins encoded by TriMV and WSMV do not prevent the formation of vsiRNAs; thus, the synergistic effect observed is independent from RNA-silencing mediated vsiRNA biogenesis. The high-resolution map of endogenous and vsiRNAs from WSMV- and/or TriMV-infected wheat cultivars may form a foundation for understanding the virus-host interactions, the effect of synergistic interactions on host defense, and virus resistance mechanisms in wheat.

The Relationship Between Yield and Fructan Exo-Hydrolases Activity in Two Drought Resistant Wheat Cultivars Grown Under Different Fertilizer and Tillage Treatments

Using two drought resistant wheat (Triticum aestivum L.) cultivars, ‘Changwu134’ and ‘Changhan58,’ a field experiment was conducted in ChangWu Agro-ecological Experiment Station on China's Loess Plateau during 2008 and 2009 to compare the effects of different fertilizer and tillage treatments on the fructan contents as well as fructan exo-hydrolase (FEH) activity in relation to wheat yield. We found that ‘Changhan58’ had greater yield and fructan content in the penultimate internode and higher FEH activity than did ‘Changwu134.’ For ‘Changhan58.’ applying 195 kg·ha−1(120 +75) N plus 45000 kg·ha−1 of pig manure and 120 kg·ha−1 phosphate under conservation tillage produced the highest yield (6769 ka/ha), fructan content in penultimate internode, water use efficiency (WUE), as well as FEH activity among the fertilizer and tillage treatments. Therefore, routine soil management for wheat should focus on combined use of manures and inorganic fertilizer to enhance the amount and transportation efficiency of WSC and ultimately ensure greater yield.

Comparative aggressiveness of Microdochium nivale and M. majus and evaluation of screening methods for Fusarium seedling blight resistance in wheat cultivars

Microdochium majus and M. nivale are the primary agents of Fusarium seedling blight (FSB) of wheat in wet and cool crop growing regions. The differential responses and plant traits (root and stem length) of eleven wheat cultivars were evaluated using three inoculation methods with M. majus or M. nivale in soil, potato dextrose agar plate or detached leaf assay to develop a reliable screening method for the identification of resistance to FSB caused by Microdochium species in wheat. Microdochium nivale was the more aggressive FSB pathogen causing 30 % higher disease severity than M. majus and impacting significantly on root length and stem length. In contrast, M. majus was more pathogenic than M. nivale on wheat leaves reducing significantly the maximum efficiency of photosystem (PS) II (Fv’/Fm’). Fv’/Fm’ provides an estimate of the efficiency of PSII photochemistry (photosynthesis) at a given photosynthetically-active photon flux density defined as PSII operating efficiency if all PSII reaction centres were ‘open’. Regression analysis suggested that reduction in stem and/or root length and Fv’/Fm’ can be used as indicators of disease severity and for the detection of tolerance in wheat cultivars to specific diseases in the Fusarium complex. There were significant interactions between genotypes and species for the assessed disease and plant traits suggesting that resistance/tolerance mechanisms and genes maybe different to disease caused by individual Microdochium species. The most resistant cultivar to FSB identified consistently using all methods was Petrus, also known to be resistant to Fusarium head blight suggesting that this cultivar may possess useful durable resistance to more than one disease in the Fusarium disease complex.

Genome-wide fungal stress responsive miRNA expression in wheat.

MicroRNAs (miRNAs) are small non-coding class of RNAs. They were identified in many plants with their diverse regulatory roles in several cellular and metabolic processes. A number of miRNAs were involved in biotic and abiotic stress responses. Here, fungal stress responsive wheat miRNAs were analyzed by using miRNA-microarray strategy. Two different fungi (Fusarium culmorum and Bipolaris sorokiniana) were inoculated on resistant and sensitive wheat cultivars. A total of 87 differentially regulated miRNAs were detected in the 8 × 15 K array including all of the available plant miRNAs. Using bioinformatics tools, the target transcripts of responsive miRNAs were predicted, and related biological processes and mechanisms were assessed. A number of the miRNAs such as miR2592s, miR869.1, miR169b were highly differentially regulated showing more than 200-fold change upon fungal-inoculation. Some of the miRNAs were identified as fungal-inoculation responsive for the first time. The analyses showed that some of the differentially regulated miRNAs targeted resistance-related genes such as LRR, glucuronosyl transferase, peroxidase and Pto kinase. The comparison of the two miRNA-microarray analyses indicated that fungal-responsive wheat miRNAs were differentially regulated in pathogen- and cultivar-specific manners.

Mapping resistance to the bird cherry-oat aphid and the greenbug in wheat using sequence-based genotyping.

Identification of novel resistance QTL against wheat aphids. First QTL-resistance report for R. padi in wheat and chromosome 2DL for S. graminum . These sources have potential use in wheat breeding. The aphids Rhopalosiphum padi and Schizaphis graminum are important pests of common wheat (Triticum aestivum L.). Characterization of the genetic bases of resistance sources is crucial to facilitate the development of resistant wheat cultivars to these insects. We examined 140 recombinant inbred lines (RILs) from the cross of Seri M82 wheat (susceptible) with the synthetic hexaploid wheat CWI76364 (resistant). RILs were phenotyped for R. padi antibiosis and tolerance traits. Phenotyping of S. graminum resistance was based on leaf chlorosis in a greenhouse screening and the number of S. graminum/tiller in the field. RILs were also scored for pubescence. Using a sequence-based genotyping method, we located genomic regions associated with these resistance traits. A quantitative trait locus (QTL) for R. padi antibiosis (QRp.slu.4BL) that explained 10.2 % of phenotypic variation was found in chromosome 4BL and located 14.6 cM apart from the pubescence locus. We found no association between plant pubescence and the resistance traits. We found two QTLs for R. padi tolerance (QRp.slu.5AL and QRp.slu.5BL) in chromosomes 5AL and 5BL, with an epistatic interaction between a locus in chromosome 3AL (EnQRp.slu.5AL) and QRp.slu.5AL. These genomic regions explained about 35 % of the phenotypic variation. We re-mapped a previously reported gene for S. graminum resistance (putatively Gba) in 7DL and found a novel QTL associated with the number of aphids/tiller (QGb.slu-2DL) in chromosome 2DL. This is the first report on the genetic mapping of R. padi resistance in wheat and the first report where chromosome 2DL is shown to be associated with S. graminum resistance.

Genetic mapping of quantitative trait loci (QTL) for resistance to septoria tritici blotch in a winter wheat cultivar Liwilla

Septoria tritici blotch (STB), caused by Mycosphaerella graminicola (anamorph Septoria tritici, syn. Zymoseptoria tritici), is present in most wheat-growing areas worldwide. Resistance breeding appears to be the most sensible approach to disease control. An attempt was made to identify loci associated with resistance to STB in a resistant winter wheat cultivar Liwilla. In the study we used a set of 74 doubled-haploid lines generated from anthers of F1 hybrids between the resistant cultivar Liwilla and susceptible cultivar Begra. Four monopycnidiospore isolates of M. graminicola with diverse pathogenicity were used in tests on seedlings under controlled growth conditions and on adult plants under polytunnel conditions over a six year period. In both environments, the percentage leaf area covered by necrosis and covered by pycnidia were measured; time to heading and plant height were also recorded for the polytunnel experiments. Seven isolate-specific quantitative trait loci (QTLs) were associated with STB resistance: QStb.ihar-3A.2, QStb.ihar-6A, QStb.ihar-7A.2, QStb.ihar-1B, QStb.ihar-2B.2, QStb.ihar-3B, and QStb.ihar-5D. QTL on chromosome 5D and 7A represent novel STB resistance loci. The phenotypic variance explained by individual QTLs ranged from 9.5 % to 50.3 %. Three QTLs detected on chromosomes 3A, 7A and 1B showed major effects and were detected consistently in different environments. The locations of QStb.ihar-3A.2 and QStb.ihar-1B coincide with the resistance genes Stb6 and Stb11, respectively. Locus QStb.ihar-3B and a QTL for time to heading mapped to the same location, but are most likely not associated. Most of the mapped QTLs explain the resistance associated with both low necrosis and low pycnidia coverage.

Wheat stripe (yellow) rust caused by Puccinia striiformis f. sp. tritici.

Stripe (yellow) rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a serious disease of wheat occurring in most wheat areas with cool and moist weather conditions during the growing season. The basidiomycete fungus is an obligate biotrophic parasite that is difficult to culture on artificial media. Pst is a macrocyclic, heteroecious fungus that requires both primary (wheat or grasses) and alternate (Berberis or Mahonia spp.) host plants to complete its life cycle. Urediniospores have the capacity for wind dispersal over long distances, which may, under high inoculum pressure, extend to thousands of kilometres from the initial infection sites. Stripe rust, which is considered to be the current major rust disease affecting winter cereal production across the world, has been studied intensively for over a century. This review summarizes the current knowledge of the Pst-wheat pathosystem, with emphasis on the life cycle, uredinial infection process, population biology of the pathogen, genes for stripe rust resistance in wheat and molecular perspectives of wheat-Pst interactions. The stripe rust pathogen, Puccinia striiformis Westend. (Ps), is classified in kingdom Fungi, phylum Basidiomycota, class Urediniomycetes, order Uredinales, family Pucciniaceae, genus Puccinia. Ps is separated below the species level by host specialization on various grass genera, comprising up to nine formae speciales, of which P. striiformis f. sp. tritici Erikss. (Pst) causes stripe (or yellow) rust on wheat. Uredinial/telial hosts: Pst mainly infects common wheat (Triticum aestivum L.), durum wheat (T. turgidum var. durum L.), cultivated emmer wheat (T. dicoccum Schrank), wild emmer wheat (T. dicoccoides Korn) and triticale (Triticosecale). Pst can infect certain cultivated barleys (Hordeum vulgare L.) and rye (Secale cereale L.), but generally does not cause severe epidemics. In addition, Pst may infect naturalized and improved pasture grass species, such as Elymus canadensis L., Leymus secalinus Hochst, Agropyron spp. Garetn, Hordeum spp. L., Phalaris spp. L and Bromus unioloides Kunth. Pycnial/aecial (alternative) hosts: Barberry (Berberis chinensis, B. koreana, B. holstii, B. vulgaris, B. shensiana, B. potaninii, B. dolichobotrys, B. heteropoda, etc.) and Oregon grape (Mahonia aquifolium). Stripe rust appears as a mass of yellow to orange urediniospores erupting from pustules arranged in long, narrow stripes on leaves (usually between veins), leaf sheaths, glumes and awns on susceptible plants. Resistant wheat cultivars are characterized by various infection types from no visual symptoms to small hypersensitive flecks to uredinia surrounded by chlorosis or necrosis with restricted urediniospore production. On seedlings, uredinia produced by the infection of a single urediniospore are not confined by leaf veins, but progressively emerge from the infection site in all directions, potentially covering the entire leaf surface. Individual uredinial pustules are oblong, 0.4-0.7 mm in length and 0.1 mm in width. Urediniospores are broadly ellipsoidal to broadly obovoid, (16-)18-30(-32) × (15-)17-27(-28) μm, with a mean of 24.5 × 21.6 μm, yellow to orange in colour, echinulate, and with 6-18 scattered germ pores. Urediniospores can germinate rapidly when free moisture (rain or dew) occurs on leaf surfaces and when the temperatures range is between 7 and 12 °C. At higher temperatures or during the later growing stages of the host, black telia are often produced, which are pulvinate to oblong, 0.2-0.7 mm in length and 0.1 mm in width. The teliospores are predominantly two-celled, dark brown with thick walls, mostly oblong-clavate, (24-)31-56(-65) × (11-)14-25(-29) μm in length and width, and rounded or flattened at the apex.

Potassium phosphate induces tolerance against the Russian wheat aphid (Diuraphis noxia, Homoptera: Aphididae) in wheat

Diuraphis noxia Kurdjumov is an aphid pest that hampers the global production of wheat (Triticum aestivum L.). Infestation of wheat by D. noxia reduces crop yield and sometimes leads to the death of susceptible cultivars. To date resistant cultivars have been used to control infestations. However, the development of resistance-breaking aphid biotypes is complicating this management strategy. This study aimed to ascertain the effect that 25 mM potassium phosphate (K3PO4) treatment has on inducing resistance in wheat against D. noxia. The effects of potassium phosphate on induced resistance against D. noxia were determined using gene regulation and enzymatic levels of lipoxygenase (EC 1.13.11) and phenylalanine ammonia lyase (EC 4.3.1.24). The results indicated that the treatment of both susceptible (Scheepers) and resistant (Tugela DN) wheat cultivars with potassium phosphate induces genes differentially. A phenotypic study showed delayed development and less severity of symptoms with decreased numbers of aphids feeding on plants treated with potassium phosphate in comparison with untreated plants for both resistant and susceptible cultivars. The results from the gene expression and enzyme activity studies indicated that both of the induced systemic resistance-linked genes were similarly regulated after potassium phosphate treatment. The data strongly support treatment of wheat with potassium phosphate to induce tolerance against D. noxia.

Long non-coding RNAs in wheat are related to its susceptibility to powdery mildew

To identify genes involved in the susceptibility to powdery mildew in wheat, genechip hybridization experiments were performed applying interactions between resistant and susceptible wheat cultivars and powdery mildew. Ten genes were found to express exclusively in the susceptible host after inoculation. The single cell transient expression experiments revealed that the RNA interference (RNAi) of two expressed sequence tag (EST) sequences (accession No. BQ168479 and CA648596) could enhance host resistance by 22 and 15 %, respectively. Full-length cDNA cloning revealed that they represented long non-coding RNAs (lncRNAs) and markedly accumulated during the powdery mildew primary infection.

Genome-wide association analysis identified SNPs closely linked to a gene resistant to Soil-borne wheat mosaic virus

Using association and linkage mapping, two SNP markers closely linked to the SBWMV resistance gene on chromosome 5D were identified and can be used to select the gene in breeding. Soil-borne wheat mosaic virus (SBWMV) disease is a serious viral disease of winter wheat growing areas worldwide. SBWMV infection can significantly reduce grain yield up to 80 %. Developing resistant wheat cultivars is the only feasible strategy to reduce the losses. In this study, wheat Infinium iSelect Beadchips with 9 K wheat SNPs were used to genotype an association mapping population of 205 wheat accessions. Six new SNPs from two genes were identified to be significantly associated with the gene for SBWMV resistance on chromosome 5D. The SNPs and Xgwm469, an SSR marker that has been reported to be associated with the gene, were mapped close to the gene using F6-derived recombinant inbred lines from the cross between a resistant parent 'Heyne' and a susceptible parent 'Trego'. Two representative SNPs, wsnp_CAP11_c209_198467 and wsnp_JD_c4438_5568170, from the two linked genes in wheat were converted into KBioscience Competitive Allele-Specific Polymerase assays and can be easily used in marker-assisted selection to improve wheat resistance to SBWMV in breeding.

Variations for Fusarium head blight resistance associated with genomic diversity in different sources of the resistant wheat cultivar 'Sumai 3'.

Fusarium head blight (FHB), caused by Fusarium graminearum, is a serious disease of wheat (Triticum aestivum L.) associated with contamination by the mycotoxin deoxynivalenol (DON). The FHB-resistant wheat cultivar ‘Sumai 3’ has been used extensively around the world. The existence of variation in FHB resistance among ‘Sumai 3’ accessions has been discussed. In this study, genetic variation among ‘Sumai 3’ accessions collected from six countries were identified using SSR markers; our results demonstrate unique chromosome regions in Sumai 3-AUT and Sumai 3-JPN (‘Sumai 3’ accessions from Austria and Japan, respectively). Field evaluation indicated strong resistance to FHB in Sumai 3-AUT. The polymorphic rate (number of polymorphic markers/number of available markers × 100) based on a DArT array was 12.5% between the two ‘Sumai 3’ accessions. Genotyping for DNA markers flanking FHB-resistant quantitative trait loci (QTLs) revealed genetic variations for the QTL regions on 5AS and 2DS; however, no variation was observed for the QTL regions on 3BS and 6B. Thus, the variation in FHB resistance among ‘Sumai 3’ accessions in the field is due to genetic diversity.

Stripe rust resistance and genes in Chinese wheat cultivars and breeding lines

AbstractStripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most important diseases on wheat in China. To assess resistance in wheat cultivars and breeding lines in China, 330 leading cultivars and 164 advanced breeding lines were evaluated with stripe rust. In the greenhouse tests, seedlings of the entries were inoculated separately with several Pst pathotypes. In the field tests, the entries were evaluated for stripe rust resistance in Yangling, Shaanxi Province artificially inoculated and in Tianshui, Gansu Province under natural infection of Pst. The oversummering/wintering and spring epidemic zones of resistance genes were postulated using molecular markers for Yr5, Yr9, Yr10, Yr15, Yr17, Yr18, and Yr26, in combination with resistance spectra. Out of the 494 wheat entries, 16 (3.24 %) entries had all-stage resistance (ASR) in all race tests, 99 (20.04 %) had adult-plant resistance (APR), 28 (5.67 %) were considered to have slow-rusting (SR), and 351 (71.05 %) were susceptible to one or more races in both seedling and adult-plant stages. Advanced breeding lines had a higher percentage (37.2 %) of resistant entries (The sum of ASR, APR and SR) than leading cultivars (24.85 %). Among the epidemic regions, southern Gansu had a higher percentage of resistant entries than any other regions. Based on stripe rust reactions and molecular markers, two cultivars were found to possibly have Yr5 while no entries have Yr10 or Yr15. Resistance genes Yr9, Yr17, Yr18, and Yr26 were found in 134 (29.4 %), 45 (9.1 %), 10 (2 %), and 15 (3 %) entries, respectively.

Expression of a potato antimicrobial peptide SN1 increases resistance to take-all pathogen Gaeumannomyces graminis var. tritici in transgenic wheat

Take-all, caused by soil-borne fungus Gaeumannomyces graminis var. tritici (Ggt), is a devastating root disease of wheat (Triticum aestivum) worldwide. Breeding resistant wheat cultivars is the most promising and reliable approach to protect wheat from take-all. Currently, no resistant wheat germplasm is available to breed cultivars using traditional methods. In this study, gene transformation was carried out using Snakin-1 (SN1) gene isolated from potato (Solanum tuberosum) because the peptide shows broad-spectrum antimicrobial activity in vitro. Purified SN1 peptide also inhibits in vitro the growth of Ggt mycelia. By bombardment-mediated method, the gene SN1 was transformed into Chinese wheat cultivar Yangmai 18 to generate SN1 transgenic wheat lines, which were used to assess the effectiveness of the SN1 peptide in protecting wheat from Ggt. Genomic PCR and Southern blot analyses indicated that the alien gene SN1 was integrated into the genomes of five transgenic wheat lines and heritable from T₀ to T₄ progeny. Reverse transcription-PCR and Western blot analyses showed that the introduced SN1 gene was transcribed and highly expressed in the five transgenic wheat lines. Following challenging with Ggt, disease test results showed that compared to segregants lacking the transgene and untransformed wheat plants, these five transgenic wheat lines expressing SN1 displayed significantly enhanced resistance to take-all. These results suggest that SN1 may be a potentially transgenic tool for improving the take-all resistance of wheat.

An Aegilops ventricosa Translocation Confers Resistance Against Root-knot Nematodes to Common Wheat.

Root knot nematodes (RKN; Meloidogyne spp.) cause severe losses worldwide to a wide range of crops. Crop rotations with resistant hosts can be used to control losses, but the wide host range of RKN limits this option. In this study, we found that the wheat cultivar Lassik is resistant to several isolates of the RKN species M. incognita and M. javanica, including those that can reproduce on tomato with the resistance gene Mi-1. Comparison of near-isogenic lines of wheat showed that the wheat resistance gene(s) is localized within a segment of the short arm of chromosome 2N from Aegilops ventricosa (Zhuk.) Chennav translocated into common wheat (Triticum aestivum L.) chromosome arm 2AS and is associated with a highly significant decrease in RKN eggs in the roots. This RKN resistance gene has been assigned the name Rkn3. While wheat itself is tolerant of RKN infection, a microplot experiment coupled with tomato bioassays showed less RKN root galling in the tomato samples grown in soil from the previous microplots including RKN resistant wheat varieties than in those including a susceptible wheat isogenic line. This result suggests that rotation with Rkn3 resistant wheat cultivars has the potential to be a valuable component of nematode management for crops that are highly susceptible to nematode damage and for which alternative strategies are limited.