Bgt Isolates Research Articles

Virulence and Genetic Diversity of Blumeria graminis f． sp． tritici Collected from Shandong and Hebei Provinces

Powdery mildew caused by Blumeria graminis f.sp.tritici(Bgt) is one of the most important diseases that damages wheat(Triticum aestivum L.) production in China.Analysis of virulence structure and effectiveness of resistance genes is important in controlling powdery mildew with host resistance.This study was conducted to test virulence structures of 41 isolates collected from Shandong and Hebei provinces in 2011.The genetic diversity of these isolates was also analyzed using SSR markers.The virulence frequencies of isolates tested ranged from 0.35(Bg40-2,Yantai,Shandong) to 0.74(Bg46-1,Pingdu,Shandong).The mean virulence frequency for the isolates from Shandong Province was not significantly different from that of the isolates from Hebei Province.Except for a few resistance genes such as Pm17,the virulence frequencies of isolates from Shandong and Hebei provinces on most resistance genes were not different.None of the isolates tested was virulent on Pm24 carried by the Chinese landrace Chiyacao.A few isolates were virulent on Pm1c,Pm16,Pm20,PmH,and Mlxbd.Two isolates from Handan and Huanghua of Hebei Province were virulent on Pm21,but none of the isolates from Shandong Province was virulent on Pm21.The virulence frequencies for Pm5e,Pm6,Pm12,Pm13,Pm17,Pm40,Pm2+6,and Pm5+6 ranged from 0.18 to 0.48.Genes Pm1a,Pm3a,Pm3c,Pm3g,Pm4a,Pm4b,Pm4c,Pm5a,Pm7,Pm8,Pm19,Pm33,Pm43,PmY39,PmPS5A,and PmDR147 had the virulence frequencies over 0.6.Analysis of genetic diversity indicated that the genetic variation of Bgt isolates occurred within the population,and gene flow occurred among isolates.Although some single spore progenies from the same location were clustered together,some were not classified into the same cluster,indicating the variation in their genetic bases.The polymorphism of virulence patterns for various resistance genes was not necessarily consistent with the DNA polymorphism as revealed by SSR markers.

Identification of Pm8 Suppressor at the Pm3 Locus in Soft Red Winter Wheat

ABSTRACTThe 1BL.1RS wheat (Triticum aestivum L.)–rye (Secale cereale L.) translocation possesses genes Pm8, Yr9, Lr26, and Sr31 for resistance to several major fungal pathogens of small grain cereals. However, not all wheat cultivars with the 1RS translocation are resistant to Pm8‐avirulent isolates of Blumeria graminis f. sp. tritici (Bgt), the causal pathogen of wheat powdery mildew. A suppressor is postulated to limit the function of Pm8 in certain genetic backgrounds, such as ‘AGS 2000’. To illustrate the genetic basis of the suppressor in AGS 2000, a 178 recombinant inbred line (RIL) population was used by crossing AGS 2000 with another 1BL.1RS cultivar Pioneer 26R61 (Pm8 effective). A single Bgt isolate, Ken‐2‐5, avirulent to Pm8 and virulent to Pm3a was chosen to inoculate the entire RIL population at the seedling stage. One major quantitative trait locus (QTL), QSuPm.uga‐1AS, was stably detected as having an inhibiting effect on Pm8 in AGS 2000, and the QTL was postulated to be Pm3a based on its location. Further evidence of the Pm8‐suppressing nature of Pm3a was obtained when eight lines from the 2010 Gulf Atlantic Wheat Nursery were inoculated with Ken‐2‐5. The eight lines all have Pm8 (1BL.1RS) but were susceptible, as they also have Pm3a. In addition, a functional locus, QPm.uga‐7AL, was identified in Pioneer 26R61, where it accounted for up to 41% of phenotypic variation in resistance to isolate Ken‐2‐5. QPm.uga‐7AL was flanked by simple sequence repeat (SSR) markers Xcfa2257 and Xwmc525 on 7AL, and its relationship with other known Pm loci on this chromosome arm remains uncertain.

Molecular mapping of a powdery mildew resistance gene in common wheat landrace Baihulu and its allelism with Pm24

Powdery mildew is one of the most devastating diseases of wheat in areas with cool and maritime climates. Chinese wheat landrace Baihulu confers a high level of resistance against a wide range of Blumeria graminis DC f. sp. tritici (Bgt) races, especially those currently prevailing in Shaanxi. The objectives of this study were to determine the chromosome bin location of the mlbhl gene from Baihulu and its allelism with Pm24. To investigate the inheritance of powdery mildew resistance and detect adjacent molecular markers, we constructed a segregating population of 301 F(2) plants and corresponding F(2:3) families derived from Baihulu/Shaanyou 225. Genetic analysis revealed that a single dominant gene was responsible for seedling stage powdery mildew resistance in Baihulu. A genetic map comprising Xgwm106, Xgwm337, Xgwm1675, Xgwm603, Xgwm789, Xbarc229, Xgpw4503, Xcfd72, Xcfd83, Xcfd59, Xcfd19, and mlbhl spanned 28.2 cM on chromosome 1D. Xgwm603/Xgwm789 and Xbarc229 were flanking markers tightly linked to mlbhl at genetic distances of 1.5 and 1.0 cM, respectively. The mlbhl locus was located in chromosome bin 1DS 0.59-1.00 delimited by the SSR markers Xgwm337 and Xbarc229. When tested with a differential array of 23 Bgt isolates Baihulu displayed a response pattern that was clearly distinguishable from that of Chiyacao and varieties or lines possessing documented Pm genes. Allelism analysis indicated that mlbhl is a new gene, either allelic or closely linked with Pm24. The new gene was designated Pm24b.

Genetic analysis and molecular mapping of a new powdery mildew resistant gene Pm46 in common wheat

Powdery mildew (PM), caused by Blumeria graminis f. sp. tritici (Bgt), has become a serious disease and caused severe yield losses in the wheat production worldwide. Resistance gene(s) in wheat cultivars can be quickly overcome by newly evolved pathogen races when these genes are employed for long time or in a large area. It is urgent to search for new sources of resistance to be used in wheat breeding. Tabasco is a German resistant cultivar and a new source of resistance gene(s) to PM. An F(2) population was developed from a cross between Tabasco and a Chinese susceptible cultivar Ningnuo 1. Infection types in 472 F(2) plants and 436 F(2-3) families were evaluated by inoculating plants with isolate Bgt19. Results showed that a single dominant gene, designed Pm46, controlled powdery mildew resistance in Tabasco. This gene was located to the short arm of chromosome 5D (5DS) and flanked by simple sequence repeat markers Xgwm205 and Xcfd81 at 18.9 cM apart. Because another resistance gene Pm2 was also located on 5DS, 15 Bgt isolates were used to inoculate Tabasco and Ulka/8*Cc (Pm2 carrier). The results showed that Tabasco was highly resistant to all of the 15 isolates tested, while Ulka/8*Cc was susceptible to 4 of the isolates, suggesting that Tabasco may carry resistant gene(s) different from Pm2 gene in Ulka/8*Cc. To test the allelism between Pm46 and Pm2, an F(2) population between Tabasco and Ulka/8*Cc was developed. Isolate Bgt2, avirulent to both parents, was used to evaluate the F(2) population and two susceptible plants were identified from 536 progenies with F(2) plants. This result indicated that Pm46 is not allelic to Pm2. Therefore, Pm46 is a new gene for PM resistance identified in this study.

Molecular detection of rye (Secale cereale L.) chromatin in wheat line 07jian126 (Triticum aestivum L.) and its association to wheat powdery mildew resistance

Powdery mildew (Pm), caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most serious diseases for common wheat in many regions around the world. Seeking for new resistance source is urgently required to meet the challenge of the rapid loss of resistance due to the co-evolution of the pathogen’s virulence. Wheat line 07jian126 (Triticum aestivum L.) is highly resistant to the Pm disease prevailing in Sichuan province of China. Previous study showed that a SSR marker Xbarc183 was linked to the Pm resistance in 07jian126, which might be controlled by a single dominant gene, designated as Pm07J126. In this study, two additional F2 populations were used to confirm the linkage between Pm07J126 and Xbarc183. Furthermore, rye chromatin was detected in 07jian126 by molecular analysis of a rye-specific SCAR marker O5 which co-segregated with Pm07J126. This result indicated that Pm07J126 might originate from rye. The reaction patterns to 21 Bgt isolates and molecular marker analysis implied that Pm07J126 might be different from the known rye-derived Pm genes Pm7, Pm8, Pm17 and PmJZHM2RL. Chromosome observation, molecular marker, and A-PAGE analysis suggested that 07jian126 might be a rye introgression line and neither contain 1RS translocation nor secalins gene. Consequently, 07jian126 could be considered as a valuable resource for Pm resistance development of wheat. Besides, the molecular markers Xbarc183 and O5 are useful in marker-assisted selection of Pm07J126 in wheat breeding programs.

Identification and mapping of two powdery mildew resistance genes in Triticum boeoticum L.

Powdery mildew (PM) caused by Blumeria graminis f. sp. tritici (Bgt), is one of the important foliar diseases of wheat that can cause serious yield losses. Breeding for cultivars with diverse resources of resistance is the most promising approach for combating this disease. The diploid A genome progenitor species of wheat are an important resource for new variability for disease resistance genes. An accession of Triticum boeoticum (A(b)A(b)) showed resistance against a number of Bgt isolates, when tested using detached leaf segments. Inheritance studies in a recombinant inbred line population (RIL), developed from crosses of PM resistant T. boeoticum acc. pau5088 with a PM susceptible T. monococcum acc. pau14087, indicated the presence of two powdery mildew resistance genes in T. boeoticum acc. pau5088. Analysis of powdery mildew infection and molecular marker data of the RIL population revealed that both powdery mildew resistance genes are located on the long arm of chromosome 7A. Mapping was conducted using an integrated linkage map of 7A consisting of SSR, RFLP, STS, and DArT markers. These powdery mildew resistance genes are tentatively designated as PmTb7A.1 and PmTb7A.2. The PmTb7A.2 is closely linked to STS markers MAG2185 and MAG1759 derived from RFLP probes which are linked to powdery mildew resistance gene Pm1. This indicated that PmTb7A.2 might be allelic to Pm1. The PmTb7A.1, flanked by a DArT marker wPt4553 and an SSR marker Xcfa2019 in a 4.3cM interval, maps proximal to PmT7A.2. PmTb7A.1 is putatively a new powdery mildew resistance gene. The powdery mildew resistance genes from T. boeoticum are currently being transferred to cultivated wheat background through marker-assisted backcrossing, using T. durum as bridging species.

Identification and characterization of a novel powdery mildew resistance gene PmG3M derived from wild emmer wheat, Triticum dicoccoides

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt) is one of the most important wheat diseases worldwide. Wild emmer wheat, Triticum turgidum ssp. dicoccoides, the tetraploid ancestor (AABB) of domesticated bread and durum wheat, harbors many important alleles for resistance to various diseases, including powdery mildew. In the current study, two tetraploid wheat mapping populations, derived from a cross between durum wheat (cv. Langdon) and wild emmer wheat (accession G-305-3M), were used to identify and map a novel powdery mildew resistance gene. Wild emmer accession G-305-3M was resistant to all 47 Bgt isolates tested, from Israel and Switzerland. Segregation ratios of F(2) progenies and F(6) recombinant inbred line (RIL) mapping populations, in their reactions to inoculation with Bgt, revealed a Mendelian pattern (3:1 and 1:1, respectively), indicating the role of a single dominant gene derived from T. dicoccoides accession G-305-3M. This gene, temporarily designated PmG3M, was mapped on chromosome 6BL and physically assigned to chromosome deletion bin 6BL-0.70-1.00. The F(2) mapping population was used to construct a genetic map of the PmG3M gene region consisted of six simple sequence repeats (SSR), 11 resistance gene analog (RGA), and two target region amplification polymorphism (TRAP) markers. A second map, constructed based on the F(6) RIL population, using a set of skeleton SSR markers, confirmed the order of loci and distances obtained for the F(2) population. The discovery and mapping of this novel powdery mildew resistance gene emphasize the importance of the wild emmer wheat gene pool as a source for crop improvement.

Identification and molecular mapping of PmHNK54: a novel powdery mildew resistance gene in common wheat

With 5 figures and 2 tablesAbstractPowdery mildew of wheat is caused by Blumeria graminis (DC.) Speer f. sp. tritici (Bgt). Wheat line Zheng 9754 is resistant in Henan Province. In seedling tests with seven Bgt isolates, Zheng 9754 had a different reaction pattern from those of lines Khapli with Pm4a, Armada with Pm4b, 81‐7241 with Pm4c and Lankao 906 with PmLK906. F1 hybrids, 516 F2 plants and 327 F2:3 lines derived from Zheng 9754/Chinese Spring (CS) were used for resistance gene tagging and linkage analysis. Simple sequence repeat (SSR) markers were used to test the two parents and resistant and susceptible bulks. Subsequently, three polymorphic markers were used for genotyping the F2 and F2:3 populations. Powdery mildew resistance in Zheng 9754 was conferred by a single dominant gene, tentatively designated PmHNK54, flanked by SSR markers Xgwm312, Xgwm372 and Xbarc5 on chromosome 2AL. The resistance gene was closely linked to Xbarc5 and Xgwm312, with genetic distances of 5.0 and 6.0 cM, respectively, and located on the chromosome bin 2AL‐1‐0.85 in the test with a set of deletion lines. The results suggested that PmHNK54 in Zheng 9754 is a new powdery mildew resistance gene in common wheat.

A new powdery mildew resistance allele at the Pm4 wheat locus transferred from einkorn (Triticum monococcum)

Powdery mildew is one of the most destructive foliar diseases of wheat. A set of differential Blumeria graminis f.sp. tritici (Bgt) isolates was used to test the powdery mildew response of a Triticum monococcum-derived resistant hexaploid line, Tm27d2. Segregation analysis of 95 F2:3 lines from a Chinese Spring/Tm27d2 cross revealed that the resistance of Tm27d2 is controlled by a single dominant gene. Using monosomic analysis and a molecular mapping approach, the resistance gene was localized to the terminal end of chromosome 2AL. The linkage map of chromosome 2AL consisted of nine simple sequence repeat markers and one sequence-tagged site (STS) marker (ResPm4) indicative for the Pm4 locus. According to the differential reactions of 19 wheat cultivars/lines with known powdery mildew resistance genes to 13 Bgt isolates, Tm27d2 carried a new resistance specificity. The complete association of the resistance allele with STS marker ResPm4 indicated that it represented a new allele at the Pm4 locus. This new allele was designated Pm4d. The two flanking markers Xgwm526 and Xbarc122 closely linked to Pm4d at genetic distances of 3.4 and 1.0 cM, respectively, are present in chromosome bin 2AL1-0.85-1.00.

Identification of disease resistances in wheat-Leymus multicaulis derivatives and characterization of L. multicaulis chromatin using microsatellite DNA markers

To identify resistance to Fusarium head blight (FHB), cereal yellow dwarf virus (CYDV), stem rust (Sr), and powdery mildew (Pm) in 24 common wheat (Triticum aestivum)-Leymus multicaulis addition/translocation lines that were developed cytogenetically and to verify the authenticity of these lines using microsatellite (SSR) DNA markers. Resistance to FHB was identified in the wheat-L. multicaulis addition lines, Line 9 and Line 26, which both contained L. multicaulis-specific fragments as shown by SSR markers. The translocation line, Trans 1, and the addition lines, Line 5 and Line 29, have resistance to stem rust (IT 0). Resistance to CYDV was evaluated based on virus titers measured by enzyme linked immunosorbent assay (ELISA). The addition line, Line 23, showed low virus titer (0.15), indicating resistance to CYDV. The segregation distribution of CYDV resistance in 98 F2 plants of Line 23/CS showed a significant deviation from 3:1. Inoculation with a set of 14 differential Blumeria graminis f. sp. tritici (Bgt) isolates did not detect powdery mildew resistance in translocation line Trans 1, addition line Line 9 and the amphiploid of wheat-L. multicaulis. However, Line 26 exhibited the resistance response pattern of Kavkaz, which carries Pm8, indicating that Line 26 most likely has the powdery mildew resistance gene Pm8 inherited from its parent lines Feng Kang 7 or Feng Kang 10. Twelve SSR markers, distributed on different homeologous chromosome groups of wheat, which distinguished L. multicaulis addition/translocation chromosomes, were used to verify the presence of L. multicaulis chromatin in the putative wheat-L. multicaulis addition/translocation lines. Of the 24 addition/translocation lines investigated using the 12 polymorphic SSR markers, 18 wheat-L. multicaulis derivatives showed the expected L. multicaulis-specific fragments, indicating that all of these 18 addition/translocation lines would most likely have the introgressed L. multicaulis chromosome(s). Chromosomal rearrangements also were detected in some of the wheat-L. multicaulis introgression lines.

Molecular Identification of a Powdery Mildew Resistance Gene from Common Wheat Cultivar Brock

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most important diseases of common wheat (Triticum aestivum L.) worldwide. Common wheat cultivar Brock introduced from UK is highly resistant (IT: 0;) to powdery mildew prevalent isolate E09 at the seedling and adult plant stages in North China. Genetic analysis using an F2 segregating population and F2:3 lines, derived from a cross between susceptible common wheat lines Xuezao and resistant common wheat line 3B529 (Jing 411*7//Nongda 015/Brock, F6), indicated that a single dominant gene, temporarily designated MlBrock, was responsible for the resistance of 3B529. By bulked segregant and molecular marker analyses, three polymorphic SSR markers (Xcfd81, Xcfd78, and Xgwm159) and two SCAR markers (SCAR203 and SCAR112) were found to be linked to MlBrock. Among these markers, Xcfd81 and SCAR203 were cosegregated with MlBrock, and SCAR112, Xcfd78, and Xgwm159 were linked to MlBrock with genetic distances of 0.5, 5.5, and 12.7 cM, respectively. According to the available physical bin mapping result of MlBrock cosegregated SSR marker Xcfd81 and SCAR203 in Chinese Spring, MlBrock was further located on chromosome bin 0–0.63 of 5DS. According to the infection-type of E09 Bgt isolate and mapping results, MlBrock might be powdery mildew resistance gene Pm2. The molecular markers developed in this study are useful for marker-assisted selection (MAS) and gene pyramiding of powdery mildew resistance genes in wheat breeding programs.

A real-time PCR assay for quantification of the Y136F allele in the CYP51 gene associated with Blumeria graminis f.sp. tritici resistance to sterol demethylase inhibitors

A single point mutation resulting in the replacement of TAT by TTT at codon 136 (Y136F) in the 14α-demethylase ( CYP51) gene was detected from triadimefon-resistant Blumeria graminis f.sp. tritici ( Bgt) isolates collected from different locations in China. Based on this point mutation, a pair of PCR primers Bgt136-F + Bgt136-R was developed for the specific detection of Y136F mutation. Additionally, based on the sequence of introns of the CYP51 gene from Bgt, another pair of PCR primers Bgt-F + Bgt-R was developed for specific detection of Bgt. Using these two primer pairs, a real-time PCR method was developed for rapid quantification of DMI-resistant Bgt populations from field samples.

Potentiality of different isolates of wilt fungus Fusarium oxysporum collected from rhizosphere of tomato against root-knot nematode Meloidogyne incognita

This investigation was undertaken to determine the effect of culture filtrates of different isolates of Fusarium oxysporum f. sp. lycopersici on mortality of Meloidogyne incognita juveniles and egg hatching. It was observed that different concentrations including standard extract (S.E), 1:10 and 1:100 dilutions of all fungal filtrates inhibited egg hatch when compared with control. Minimum mortality and maximum hatching was observed in BRT (showing least mortality) isolate of F. oxysporum, while maximum mortality and minimum egg hatching was recorded in BGT (showing maximum mortality) isolate. Larval mortality was decreased with a decrease in concentration and the least mortality was observed in 1:100 when compared with SE and 1:10. The potentiality of both the isolates (BRT and BGT) against root-knot nematode M. incognita was confirmed by the pathogenicity test on tomato. These observations confirmed that F. oxysporumisolates possesses variability in pathogenicity ranging from pathogenic to bio-control agent. The plants inoculated with BRT isolate failed to show wilt symptoms while plants inoculated with BGT isolate showed wilt indices.