University of Minnesota
Michael Pumphrey, Matthew Rouse
Stem rust of wheat caused by the fungal pathogen Puccinia graminis f. sp. tritici historically caused major yield losses of wheat worldwide. To understand the genetic basis of stem rust resistance in contemporary North American spring wheat, genome-wide association analysis was conducted on 250 elite lines. The lines were evaluated in separate nurseries each inoculated with a different P. graminis f. sp. tritici race for three years (2013, 2015 and 2016) at Rosemount, Minnesota. The lines were also challenged with the same four races at the seedling stage in a greenhouse facility at the USDA-ARS Cereal Disease Laboratory. A total of 22,310 high-quality SNPs obtained from the Infinium 90,000 SNPs chip were used to perform association analysis. Markers strongly associated with resistance to the four races at seedling and field environments were identified. At the seedling stage, the most significant marker-trait associations were detected in the regions of known major genes (Sr6, Sr7a and Sr9b) except for race QFCSC where a strong association was detected on chromosome arm 1AL. Markers presumably linked to Sr6 and Sr7a were associated with both seedling and field resistance to specific races. A field resistance QTL on chromosome arm 2DS was detected for response to races RCRSC and TPMKC. A QTL specific to field resistance was detected for QFCSC and TPMKC on 2BL. The markers that showed strong association signals may be useful to pyramid and track race-specific stem rust resistance genes in wheat breeding programs. We postulated the presence of Sr2, Sr6, Sr7a, Sr8a, Sr9b, Sr11, Sr12, Sr24, Sr25, Sr31, and Sr57 (Lr34) in this germplasm based on phenotypic and marker data. We found that combinations of genes conferring resistance to specific P. graminis f. sp. tritici races accounts for the prevalent stem rust resistance in North American spring wheat.
Egerton University Njoro, Kenya
Ruth Wanyera, James Owuoche, Julian Rodriguez, Annemarie Justesen, Lesley Lesley, Sridhar Bhavani, Cristobal Uauy, Mogens Hovmøller
Emergence of new virulent races of Puccinia striiformis f. sp. tritici (Pst) to stripe (yellow) rust resistance genes in wheat (Triticum aestivum L.) has historically resulted in severe yield losses worldwide. We conducted a study to characterize the virulence profiles of Pst races prevalent in Kenya from historic (1970-1992) and recent collections (2009-2014). Pst isolates collected during surveys in Kenya were characterized at the Global Rust Research Centre (GRRC), Denmark. Yellow rust differential sets (wheat lines with known Yr resistance genes), and strain-specific sequence-characterized-amplified-region (SCAR) markers were used to group the Pst isolates as Pst1 or Pst2. Virulence to Yr1, Yr2, Yr3,Yr6, Yr7, Yr8, Yr9, Yr17, Yr25, Yr27, and the seedling resistance in AvocetS were detected. A total of 12 virulence profiles /races were detected in isolates obtained during 1970 to 1992, while six races were detected from samples collected between 2009 to 2014. In both periods, races with virulence profiles Yr2, Yr6, Yr7, Yr8, Yr25, Yr27, Avs and Yr2, Yr6, Yr7, Yr8, Yr17, Yr25, AvS were common. The SCAR results revealed that both Pst1 and Pst2 strains were present in the Pst isolates tested, Pst1 even in isolates from the 1970s. Additional isolates were also identified with neither Pst1 nor Pst2 profiles. From our findings, race analysis is key to understand the race diversity and pre-breeding efforts for effective resistance gene deployment.
The University of Agriculture, Peshawar, Pakistan
Muhammad,Khan, Safi, Kathi, Zahoor, Swati, Manzoor, Hussain, Annemarie, Justesen, Muhamamd, Imtiaz, , , , , , , , , , , , , , , , , ,
Considering the importance of wheat rust diseases in Pakistan and the recent identification of yellow rust pathogen (Puccinia striiformis f. sp. tritici) centre of diversity in Pakistan, the present study was designed to assess the status of three wheat rusts across the country during 2015-16 and 2016-17 and analyze the population structure of P. striiformis f. sp. tritici . A total of 451 fields (from 68 districts) were surveyed during 2016 and 480 fields (from 69 districts) during 2017. A high yellow rust pressure was present during 2016 throughout Pakistan, while it was predominant only in the Northern half during 2017. Leaf rust was present in the central part of the country, while stem rust was only found in the south. In Sindh province (located in the south), yellow rust was reported unexpectedly with high severity (>60%) on varieties like Kiran and Galaxy during both the years. A set of 513 samples of P. striiformis were genotyped with microsatellite markers to assess the population diversity and spatial structure. and infer on the cause of epidemics in the Sindh province. Population genetics analyses confirmed a recombinant population structure across all locations except the Sindh province, where relatively lower diversity and lack of recombination signature was revealed. At least five genetic groups were identified in the overall population, which were found across all locations, except Sindh province where one of the genetic groups was predominant. The P. striiformis population from Sindh province with low diversity that caused unexpected epidemics in a relatively warmer region needs to be further investigated for specific adaptation traits. Our results confirmed the high diversity across Pakistan, which lies in the Himalayan centre of diversity of the pathogen. This high diversity was present in locations without the presence of alternate host (Berberis spp.) and could potentially be associated with regular migrants from the Berberis zone into the whole country.
Crop and Horticultural Science Research Department, Ardabil Agricultural and Natural Resources Research and Education Center, Ag
Yellow (stripe) rust caused by Puccinia striiformis f. sp. tritici is the most devastating disease of bread wheat (Triticum aestivum) in the world. A wide range of virulent yellow rust pathotypes is evolving in different regions of the world causing the breakdown of widely utilized sources of resistance in wheat. Hence, the knowledge of virulence factors of pathogen and determining of effective resistance genes in the region will enable breeders to target those useful genes in their breeding programs. During cropping seasons of 2015-2016 and 2016-2017, virulence of the wheat yellow rust was investigated by planting differential cultivars and isogenic lines in a yellow rust trap nursery in Ardabil, northwest of Iran . Results showed stripe rust infections on some cultivars carrying Yr genes such as Yr1, Yr3, and Yrsp previously known to be resistant. The virulence spectrum of race population in Ardabil was identical to the Warrior race or its variants which is different from characterized races in Ardabil by carrying virulence combination for Yr1, Yr3, Yr17, Yr32, and YrSP and is avirulent on Yr8 and Yr27. Except for Yr8, Yr17 and Yr27, the common races in Ardabil are generally avirulent on Yr1, Yr3, and YrSP. This is the first report of race population in Ardabil (Iran) which is similar to the Warrior race or its variants.
Bangladesh Agricultural Research Institute
Paritosh Kumar,Malaker, Krishna Kanta, Roy, Md. Mostofa Ali, Reza, Naresh Chandra Deb, Barma, Md., Farhad, , , , , , , , , , , , , , , , , , , ,
Leaf rust is one of the major diseases of wheat in Bangladesh. The farmer fields and trial sites were regularly surveyed for rust assessment from 2010-2011 to 2016-2017 wheat growing seasons. Disease severity was recorded following BGRI protocols. Percentage of fields infected with leaf rust and the levels of disease severity varied with genotype, year, planting time and survey sites. Timely planted wheat either escaped or had less disease compared to late planted crop. Among our cultivated varieties, Shatabdi was either free from infection or exhibited only trace severity with resistant reaction. Variety Saurav, Bijoy, BARI Gom 27 , BARI Gom 28 , BARI Gom-29 and BARI Gom-30 were consistently free from leaf rust infection. BARI Gom 25 and BARI Gom 26 showed low to moderate disease levels with MRMS-MSS reactions, while the variety Prodip demonstrated moderate to high disease severity with susceptible response and it needs to be replaced by resistant variety to sustain wheat productivity.
La Trobe University
Reem Joukhadar, Sukhwinder Singh, Francis Ogbonnaya
Synthetic hexaploid wheat (SHW), generated by crossing Triticum turgidum (AABB) with Aegilops tauschii (DD), has been exploited in improving various traits in cultivated wheat. A number of recent studies decomposed the additive variance of different traits captured by multiple sets of variants (e.g. single nucleotide polymorphisms (SNPs) located on different chromosomes or genic/intergenic regions) in both human and animal quantitative genetics studies. In this research, we dissected the additive variance explained by the three subgenomes and seven homoeologous sets of chromosomes in SHW germplasm to gain a better understanding of trait evolution in newly synthesized wheat. Our SHW germplasm lines generated by crossing improved durum parents (AABB) with Aegilops tauschii (DD) parents were phenotyped for ten fungal/nematode resistance traits. The lines were genotyped by genotyping-by-sequencing and 6,176 SNPs were mapped with missing data of less than 20%. The D subgenome dominated the additive effects and this dominance affected the A more than the B subgenome. The D subgenome exhibited a 1.8-fold higher contribution than the A subgenome across all traits. This dominance was not inflated by population structure or by longer linkage disequilibrium blocks observed in the D subgenome. The cumulative effects of the three homoeologs in each set had a significant positive correlation with their cumulative explained additive variance. Moreover, an average of 70% for each chromosomal group cumulative additive variance came from one homoeolog that had the highest explained variance within the group across all ten traits. We hypothesize that structural and functional changes during diploidization may explain chromosomal group relationships as allopolyploids maintain a balanced dosage for many genes. Our results contribute to a better understanding of trait evolutionary mechanisms in SHW, and will facilitate effective utilization of wheat relatives in breeding.
ICAR-Indian Agricultural Research Institute, Regional Station, Wellington, The Nilgiris, Tamilnadu, India
SIVASAMY,MURUGASAMY, JAYAPRAKASH, PARAMASIVAM, RAJESH KUMAR, MEENA, , , , , , , , , , , , , , , , , , , , , , , ,
Emmer wheat (Triticum dicoccum L.), tetraploid species (AABB) and spelt wheat (Triticum spelta L.), hexaploid species (AABBDD) are old world hulled wheat species cultivated centuries ago in different parts of the world. These species were later replaced by higher yielding bread and durum wheat in the last centuries. Grain yield is influenced by grain number per unit area and grain size which correlates positively with grain weight. Increasing the grain number was extensively and intensively explored in the past 100 years of wheat breeding which has nearly reached to saturation and leaves little room for further yield increase due to grain number?grain size trade off. Grain size/grain weight is believed to be major driving force for further improvement of wheat yield. Both the species have been characterised with larger grain size and higher grain weight; therefore an ideal source to improve the grain size/grain weight while maintaining the grain number per spike in the cultivated bread wheat. A total of 25 accessions each of emmer and spelt wheat with good grain size and weight were crossed with 5 elite bread wheat lines. In the F2 generation, recombinant lines with good grain size, higher grain weight and grains number were further backcrossed with bread wheat. Stable lines with free threshing were obtained at BC4F4 generations and were analysed for quality. Thousand grain weight (TGW) and harvest index (HI) ranged from 46-55g and 0.47-0.58 in stable lines respectively. Stable lines yielded 16-21% than the high yielding check while number of grains per spike was maintained as that of check. Stable lines involving spelt crosses have higher grain size, TGW and HI than emmer wheat crosses. Stable lines could be released directly as cultivar or else used as one of the parents in the wheat improvement programme.
University of Minnesota
Bedada,Girma, Bekele, Hundie, Endale, Hailu, Getaneh, Wonderufael, Bekele, Abeyo, Ayele, Badebo, Pablo, Olivera, Yue, Jin, Gordon, Cisar, Matthew, Rouse, , , , , , , , , ,
Wheat stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is a significant disease limiting wheat yield in Ethiopia. Wheat varieties such as 'Digalu' with single major-effect stem rust resistance genes have not exhibited durable resistance in Ethiopia. Identifying wheat lines with adult plant resistance (APR) has been proposed as a strategy to select for durable resistance. Our objective was to test the hypothesis that APR to stem rust is non-race-specific. We selected 31 wheat lines (including 10 durum and 21 bread wheat lines) that were susceptible as seedlings to Pgt races TTKSK, TKTTF, and TRTTF. These 31 wheat lines and Digalu were evaluated in 2014 and 2015 at the Kulumsa Agricultural Research Center, Ethiopia. The lines were planted in 1 m rows and replicated twice in separate single-race-inoculated nurseries. The three single-race nurseries inoculated with Pgt races TTKSK, TKTTF, and TRTTF were separated by at least 100 m and included selective spreaders. Plot yield, thousand kernel weight (TKW), and visual disease responses were measured for each plot. We used a least-squared means test to detect differences in coefficient of infection and TKW of each line across paired race comparisons. Lines 'Park', 'CI11469', and 'CI12818' displayed significantly different coefficient of infections between races TTKSK and TRTTF. For CI11469 and CI12818, this difference was validated by significant differences in TKW. Significant differences in TKW were also detected between various race comparisons for 'ETHBW019', 'CI14798', 'CI15159', 'CI14618', and 'CI14094'. Our data demonstrated that APR in the selected germplasm was largely non-race-specific, but there were exceptions where race-specificity of APR was detected. These results have implications for resistance breeding and monitoring: testing of breeding material against prevalent Pgt races in target environments, not relying only on hotspot screening locations, and careful monitoring of deployed APR varieties are all warranted.
State Key Laboratory of Crop Stress Biology in Arid Areas, Northwest A&F University, Yangling 712100, Shaanxi, China
Hui,Liu, Guangwei, Xing, Xiaojun, Nie, Song, Weining, , , , , , , , , , , , , , , , , , , , , ,
RNA editing is an important way to convert cytidine (C) to uridine (U) at specific sites within RNA molecules at a post-transcriptional level in the chloroplasts of higher plants. Although it has been systematically studied in many plants, little is known about RNA editing in the wheat D genome donor Aegilops tauschii L. Here, we investigated the chloroplast RNA editing of Ae. tauschii and compared it with other wheat relatives to trace the evolution of wheat. Through bioinformatics prediction, a total of 34 C-to-U editing sites were identified, 17 of which were validated using RT-PCR product sequencing. Furthermore, 60 sites were found by the RNA-Seq read mapping approach, 24 of which agreed with the prediction and six were validated experimentally. The editing sites were biased toward tCn or nCa trinucleotides and 50-pyrimidines, which were consistent with the flanking bases of editing sites of other seed plants. Furthermore, the editing events could result in the alteration of the secondary structures and topologies of the corresponding proteins, suggesting that RNA editing might impact the function of target genes. Finally, comparative analysis found some evolutionarily conserved editing sites in wheat and two species-specific sites were also obtained. This study is the first to report on RNA editing in Aegilops tauschii L, which not only sheds light on the evolution of wheat from the point of view of RNA editing, but also lays a foundation for further studies to identify the mechanisms of C-to-U alterations.
CSK Himachal Pradesh Agricultural University, Palampur, India
Aashima Bhateja, Ravi Sharma, Vijay Rana, Hanif Khan
Wheat crop is attacked by three rust diseases of which stripe rust, caused by Puccinia striiformis f. sp. tritici and leaf rust, caused by Puccinia triticina, are the most common causing greater yield losses. Thirty genotypes were studied for (APR) adult plant resistance and were evaluated in field conditions and controlled conditions. HPW 373, VW 20145, VL 3002, RKVY 231, VL 907, PBW 698 and HS 507 were found to be highly resistant to yellow rust at both seedling and adult plant stages. While, genotypes HS 490, HPW 314, HPW 360, RKVY 133, Raj 4362, DBW 113 and HPW 403 showing very low AUDPC values were found to be moderately resistant under field conditions. These lines are suggested for use in breeding program and some are in network trials for their direct release. Inheritance studies were carried out to decipher the genetics of seedling rust resistance in elite germplasm line HPW 373. The F2s were evaluated for seedling resistance against yellow rust (46S119, 78S84) and leaf rust (77-5-North American equivalent THTTM) races. Resistance in HPW 373 is controlled by single dominant gene against leaf rust (77-5) and stripe rust (78S84). Against stripe rust (46S119), resistance of HPW 373 is controlled by recessive gene. The findings are expected to contribute towards enriching diversity for leaf and stripe rust resistance in bread wheat improvement programmes.