Stem rust caused by Puccinia graminis f.sp. tritici is one of the major biotic constraints of wheat production. The disease may cause substantial quantitative and qualitative yield losses. However, much of the work in Ethiopia on this pathosystem focuses on quantitative yield loss and qualitative losses are often overlooked. Hence the current research was designed with the objectives to evaluate the effect of stem rust on physical and chemical quality of durum wheat and assess the relationships between disease intensity and quality parameters. For this purpose, a factorial field experiment was conducted at Debre Zeit Agricultural Research Centre during main and off seasons of 2016/17. The experiment involved six durum wheat varieties (Denbi, Hitosa, Tob.66, Mukiye, Ude and Mengudo) with different level of resistance to stem rust, and three Tilt spray schedules of Tilt?250 E.C at 7, 14 and 21 days. The experiment was laid out in randomized complete block design in factorial arrangements with three replications and untreated checks were included for comparison purpose. Results revealed significant variations in disease parameters and crop performance among spray schedules, wheat varieties and their interactions. Stem rust severity was the lowest on moderately susceptible and susceptible varieties treated with the Tilt at 7th day schedule. The highest stem rust severity (46.67%) was recorded on variety Hitosa without Tilt spray. Without Tilt treatment Denbi variety accounts protein content of 15.67% which is a false protein. At 7th day spray schedule this variety showed 12.90 % of grain protein content which is normal. There was a significant positive correlation between grain protein and stem rust severity (0.31**). There was significant negative relationships between terminal stem rust severity and thousand kernel weight, hectolitre weight, seed size and yield during off and main seasons were resulted, respectively.
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Stem rust (SR) and Fusarium head blight (FHB) threaten the sustainability of wheat production worldwide. Sr2 is a widely used gene conferring partial, but durable, resistance to SR. Fhb1 confers a significant level of FHB resistance, but is poorly represented in the INIA-Uruguay wheat-breeding program. Sr2 and Fhb1 are linked in repulsion (~3 cM apart) on chromosome 3B. However, lines with Sr2 and Fhb1 in coupling were recently developed at the University of Minnesota, USA (kindly provided by J. Anderson). In order to incorporate Sr2/Fhb1 into Uruguayan elite wheat cultivars the donor line was crossed and backcrossed with four cultivars lacking both genes and expressing an intermediate to low level of resistance to SR and FHB: G?nesis 2375, G?nesis 6.87, INIA Madrugador, and INIA Don Alberto. Genotypes carrying Sr2/Fhb1 were selected using molecular marker UMN10; 250 BC2F1 were obtained for each recurrent parent. BC3F1 plants positive for UMN10 will be selected. The effect of Sr2/Fhb1 on response to SR and FHB in the different genetic backgrounds will be quantified by comparing disease severities of BC3F2 homozygotes with and without the UMN10 marker. Hopefully the introduction of Sr2/Fhb1 will contribute in reducing the risk of SR and FHB in wheat crops in Uruguay.
Wheat stem rust (SR), caused by Puccinia graminis f. sp. tritici, (Pgt) is considered one of the most destructive diseases of the wheat crop. As Sr24 and Sr31 are the most widely used resistance genes in the Southern Cone of America, wheat crops in this region is under threat of SR outbreaks posed by the potential migration of virulent Pgt Ug99-lineage races (Ug99+). Efforts have to be made to develop adapted lines resistant to Ug99+. Genes Sr26, Sr32 and Sr39 are effective to both Ug99+ and local races of the pathogen. This work is aimed to pyramid two and three of the resistance genes in two locally adapted wheat cultivars (G?nesis 2375 and G?nesis 6.87). Donor lines of Sr26, Sr32 and Sr39 (developed by I. Dundas, University of Adelaide, Australia) and molecular markers Sr26#43, csSr32#1 and Sr39#22r (developed by R. Mago et al., University of Adelaide) were used. Lines with two-gene combinations were developed in two steps. First, tree-way crosses were made by crossing heterozygous F1 plants (derived from crossings donor lines) to either one of the two adapted wheat cultivars. Subsequently, tree-way F1 plants were genotyped and only those with two-gene combinations were backcrossed (BC) twice to the adapted cultivars. Among three-way F1 plants, two-genes combinations were confirmed for Sr26+Sr32 (8 out of 31), Sr26+Sr39 (2 of 115) and Sr32+Sr39 (26 out of 103). In the BC1F1 generation, Sr26+Sr32, Sr26+Sr39 and Sr32+Sr39 combinations corresponded with 9, 9 and 45 out of 99, 27 and 241 plants, respectively. In 2017, 1345 BC2F1 plants are being grown to obtain BC2F2. We plan to intercross plants with two-gene combinations to obtain lines with the three genes which will be used as sources of resistance to develop cultivars with presumably longer lasting resistance to wheat SR.
Rust diseases in wheat are the major threat to wheat production and yield gains. The breakdown in resistance of certain major genes and new emerging aggressive races of rusts are causing serious concerns in all main wheat growing areas of the world. Therefore, it is the need of the hour to search for new sources of resistance genes or QTL's for effective utilization in future breeding programs. In total 100 wheat genotypes were evaluated for seedling and adult-plant resistance to stem rust races TKTTF and TTKSK at Tel Hadya-Syria, and Njoro-Kenya, and Kelardasht-Iran. Evaluation to Yr27 virulent stripe rust race was carried out at Tel Hadya and Terbol-Lebanon research stations. In this study we used genome wide association studies (GWAS) to identify markers or QTLs linked to stem rust and stripe rust races using Diversity Arrays Technology (DArT?) in selected 35 Iranian wheat genotypes. The association of markers and phenotypes was carried out using a unified mixed-model approach (MLM) as implemented in the genome association and prediction integrated tool (GAPIT). Out of 3,072 markers, 986 were polymorphic and used for marker trait associations. A total of 44 DArT markers were identified to be significantly (p<=0.01) associated with studied traits in 16 genomic regions 1A, 1B, 2A, 4A, 6A, 7A, 1B.1R, 2B, 3B, 4B, 5B, 5B.7B, 6B, 7D and an unknown region. Among associated markers, 34 were linked to stem and nine to stripe rust. They were found on 16 genomic regions on chromosome arms 1A, 1B, 2A, 4A, 6A, 7A, 1B.1R, 2B, 3B, 4B, 5B, 5B.7B, 6B, 7D and an unknown region. Associated markers explained phenotypic variation ranging from 21 to 65%. In addition to validation of previously identified genes, this study revealed new QTL's linked to stem and stripe rust which will assist breeders to develop new resistant varieties.
Berberis species are important alternate hosts and generate new races of stem rust fungus, Puccinia graminis f. sp. tritici and yellow (stripe) rust fungus Puccinia striiformis. Berberis species are common in Kastamonu province of Turkey. In 2016 and 2017, surveys were conducted in Kastamonu province in order to elucidate aecial infection status of Berberis species in this region. In 2016, the central region and A?l?, Ara?, Daday, ?hsangazi, Seydiler, Ta?k?pr? and Tosya regions and in 2017 central region and Ara?, Daday, Han?n?, P?narba??, Seydiler, Ta?k?pr? and Tosya regions of Kastamonu province were investigated. It appears that there are at least two different Berberis species exist in that area. Berberis species showed variation in terms of fruit color and morphological characters. In 2016, 50 Berberis plants were examined and aecia were present in 38 plants (76%). Percentage of plants parts infected with aecia ranged between 3-80%. In 2017, 64 Berberis plants were examined. Aecia were present in 34 plants (53%). Percentage of plants parts infected with aecia ranged between 3-85%. Aecia were mainly observed on leaves but also observed on other plant parts including flower parts, fruit and young twigs. The role of these aecia and Berberis spp. on rust diseases in Kastamonu province of Turkey should be investigated.
This study was supported by General Directorate of Agricultural Research and Policies, Turkey (Project No: TAGEM-BS-15\12-01\02-02).
A total of 41 bread wheat (Triticum aestivum L.) varieties have been released so far in Nepal since 1960. Farmers have been gradually adopting newly released varieties due to disease and lodging resistance, better yield performance and good taste. In Nepal, wheat area coverage, production and productivity have been increased by almost seven, sixteen and two folds, respectively in the last 56 years. Performance of varieties varies from one region to another. Yellow rust is the major problems in hills while leaf rust is the primary issue on the plains. Stem rust is sporadic in localized areas of Nepal. Wheat research program in Nepal has released 9 wheat varieties resistant to Ug99 namely Vijaya, Tilottama, Banganga, Gaura, Dhaulagiri, Danphe, Sworgadwari, Munal and Chyakhura. Vijay, Tilottama and Banganga are also resistant to leaf rust while, Dhaulagiri, Danphe, Sworgadwari, Munal and Chyakhura are resistant to yellow rust. Since the release of Vijay, the first Ug99 resistant variety in Nepal during 2010, source seed production of rust resistant varieties has been increasing significantly each year with present coverage under these varieties being around 40%. WK 1204 has been occupied 35% area in hills of Nepal. Seed production and distribution of such high yielding disease resistant varieties through public-private partnership is leading to quality seed supply for varietal diversity and better food security in the country.
In 2016 rust surveys were carried out in all the four key wheat growing regions: South Rift (June, July), Mount Kenya (July), North Rift (September) and Central Rift (part of August and September). A total of 304 farms were sampled. Stem rust was detected in 235 (78.3%), yellow rust in twenty-eight (9.3%) and leaf rust in fourteen (4.7%) of the farms. Stem and yellow rust were detected in all the wheat growing regions while leaf rust was detected in South, North and Central Rift. Stem rust infection ranged from TR to 90S with maximum infection in Central Rift (88.3%), Mt. Kenya region (80.3%); South Rift (76.5%) and North Rift (72.4%). Yellow rust infection ranged TR to 60S with maximum infection in Central Rift (16.7%); North Rift(13.3 %) and minimum infection in South Rift( 4.9%),) and Mt. Kenya region ( 1.7%). Leaf rust infection ranged from trace to 50S with maximum infection in North Rift (10.2%) minimum infection in Central Rift (3.3 %) and South Rift (1.2%). Fifty percent of the eight previously released wheat varieties are now susceptible to the Ug99 race. Race analysis results from AAFC Canada suggested the presence of TTKSK which was dominating in North Rift and TTKSK, TTKST and TTTTF were dominant in the screening nursery at Njoro. Yellow rust in the region has increased in the current year owing to the incursion of a probable new race AF2012 which has resulted in increased disease severity on varieties and materials tested in the International nurseries at KALRO, Njoro.
Ug99 is a devastating race of Puccinia graminis f.sp. tritici possessing virulence against resistant genes Sr31 and Sr24. This race is highly adoptive and has spread quite rapidly with 13 known variants covering 13 different countries. For reducing the vulnerability of wheat in south Asia to the Ug99, breeding durable resistant varieties is important. India, second largest wheat producer, falls in the predicted pathway of Ug99. Most of the Indian germplasm possesses Sr31 and Sr24 in their background. HUW468, a well adopted variety of north eastern plains zone (NEPZ) of India, carries durable resistance gene Sr2. To strengthen it, a MABB program was initiated to introgressed two major genes (Sr50 and SrWeb) using a donor line PMBWIR4 from CIMMYT. The foreground selection was performed with Xgwm47 for SrWeb and IB267 for Sr50 followed by the background selection by using 128 polymorphic SSR markers covering all chromosomes. Backcross progenies of HUW468 were screened in the field condition by using of Pgt race 21A-2 at IARI, Regional Station, Indore located in the central India. Superior selected lines from BC2F4:5 generation was planted at three locations in India namely; Varanasi, Indore and Dharwad. HUW468-09-25-47-09 and HUW468-09-25-47-56 were selected from BC2F5 generation having Sr50 and SrWeb along with Sr2 gene, superior agronomic performance and with 93.5% and 92.7% genome recovery, respectively. These two lines also possess 6-10 % yield superiority over the recipient parent HUW468. These lines have been submitted for registration in NBPGR (National Bureau of Plant Genetic Resources), India.
Multiple rust resistance gene combinations are considered as a practical solution for providing durable rust resistance and preventing resistance breakdown arising from single gene deployment. The stem rust resistance locus Sr26, originally derived from Thinopyrum ponticum and introgressed into wheat as a chromosome translocation, is one of the very few genes conferring durable resistance for almost 40 years to all known races of stem rust, including the highly virulent stem rust race Ug99 (TTKSK) and its derivatives (Dundas et al. 2015). To understand the underlying mechanisms of its unusual long-term effectiveness and to explore allelic diversity in different Th. ponticum accessions for other functional alleles that may offer new sources of resistance, we used comparative genomics and gene capture techniques (Resistance gene enrichment sequencing, RenSeq) as complementary strategies for isolating the target gene (Steuernage et al. 2016). Sr26 region was first mapped using NB-LRR (Nucleotide-binding site and leucine-rich repeat) sequences from the orthologous gene members located on the long arm of chromosome 6D from Aegilops tauschii (the D-genome donor of wheat) reference genome. Subsequently, we revealed a cluster of NB-LRR sequences located at the distal end of the Th. ponticum introgression segment that were absent in the smallest interstitial Sr26 deletion mutant. Therefore, we substantially narrowed down the genetic interval for Sr26. In addition to this approach, we subjected the mutant population to RenSeq pipeline. A candidate gene of Sr26 has been successfully identified to be a NBS-LRR type resistance gene. Validation of the gene candidate by complementation studies is currently in progress. In order to enhance durable resistance, genetic stocks of Sr26 from different backgrounds as well as a panel of Sr26-APR (Adult Plant Resistance) gene combinations have been generated to further investigate the resistance response of Sr26 in combination with different multi-pathogen APR genes.
To monitor evolution and pathogenic variability of wheat stem rust pathogen (Puccina graminis f. sp. tritici) in Australia, the Australian Cereal Rust Control program regularly conducts national annual surveys. Recently, we detected a new pathotype 34-1,2,5,7 (culture # 661) virulent on stem rust resistance genes Sr5, Sr6, Sr7b, Sr9g, Sr11, Sr15 and Sr17. Although virulent on Sr11, this pathotype produced a low infection type (IT 22+C/X) on the Sr11-differential genotype Yalta, indicating that Yalta carries an uncharacterised resistance (SrY) in addition to Sr11. To characterize SrY, we screened a RIL population Yalta/W2691 (104 lines) with two pathotypes: 21-0 (avirulent on Sr11 or AA) and the newly identified 34-1,2,5,7 (virulent on Sr11 but avirulent on SrY or BB). Yalta produced low infection types, "1C" and "22+C/X" with pathotypes 21-0 and 34-1,2,5,7, respectively, whereas W2691 was susceptible to both pathotypes. The population segregated for AA/aa (35 Res: 69 Sus) and BB/bb (36 Res: 68 Sus) loci with pathotypes 21-0 and 34-1,2,5,7, respectively. The observed segregation (AA/aa and BB/bb) however failed to fit with predicted single gene 1:1 model (P<0.05) with both pathotypes. Joint segregation analysis (AA/aa vs BB/bb) also significantly deviated (P<0.01) from 1:1:1:1 (AABB:AAbb:aaBB:aabb) genetic model. It appears that population is skewed towards susceptibility in each case either by chance or differential gametic transmission as reported previously in progenies derived from crosses involving variety Yalta. The segregation pattern (AABB and aabb) with two pathotypes was, however, highly coupled apart from 13 lines, of which, 6 lines (AAbb) were susceptible with 21-0 and resistant with 34-1,2,5,7, and 7 lines (aaBB) resistant with 21-0 and susceptible with 34-1,2,5,7, showing that the two loci are linked (?2 linkage = 76.9; P<0.001) and located very close to each other. If that is the case, it may imply that SrY is common in wheats carrying Sr11. Cultivar Charter has been used in India to differentiate pathotypes virulent for Sr11, suggesting that Charter also carries a second stem rust locus (SrC) possibly corresponding with SrY. Further studies and mapping work are underway to determine the genetic relationship between SrY, SrC and Sr11.