Adult Plant Growth Stages Research Articles

Mapping of Leaf Rust Resistance Loci in Two Kenyan Wheats and Development of Linked Markers.

Leaf rust caused by the pathogen Puccinia triticina (Pt) is a destructive fungal disease of wheat that occurs in almost all wheat-growing areas across the globe. Genetic resistance has proven to be the best solution to mitigate the disease. Wheat breeders are continuously seeking new diversified and durable sources of resistance to use in developing new varieties. We developed recombinant inbred line (RIL) populations from two leaf rust-resistant genotypes (Kenya Kudu and AUS12568) introduced from Kenya to identify and characterize resistance to Pt and to develop markers linked closely to the resistance that was found. Our studies detected four QTL conferring adult plant resistance (APR) to leaf rust. Two of these loci are associated with known genes, Lr46 and Lr68, residing on chromosomes 1B and 7B, respectively. The remaining two, QLrKK_2B and QLrAus12568_5A, contributed by Kenya Kudu and AUS12568 respectively, are putatively new loci for Pt resistance. Both QLrKK_2B and QLrAus12568_5A were found to interact additively with Lr46 in significantly reducing the disease severity at adult plant growth stages in the field. We further developed a suite of six closely linked markers within the QLrAus12568_5A locus and four within the QLrKK_2B region. Among these, markers sunKASP_522 and sunKASP_524, flanking QLrAus12568_5A, and sunKASP_536, distal to QLrKK_2B, were identified as the most closely linked and reliable for marker-assisted selection. The markers were validated on a selection of 64 Australian wheat varieties and found to be polymorphic and robust, allowing for clear allelic discrimination. The identified new loci and linked molecular markers will enable rapid adoption by breeders in developing wheat varieties carrying diversified and durable resistance to leaf rust.

Phenotyping and Identification of Molecular Markers Associated with Leaf Rust Resistance in the Wheat Germplasm from Kazakhstan, CIMMYT and ICARDA.

Leaf rust (LR) is the most widespread disease of common wheat worldwide. In order to evaluate leaf rust resistance, 70 uncharacterized wheat cultivars and promising lines with unknown leaf rust resistance genes (Lr genes) were exposed to Kazakhstani Puccinia triticina (Pt) races at the seedling stage. Field tests were performed to characterize leaf rust responses at the adult plant growth stage in the 2020-2021 and 2021-2022 cropping seasons. The wheat collection showed phenotypic diversity when tested with two virulent races of Pt. Thirteen wheat genotypes (18.6%) showed high resistance at both seedling and adult plant stages. In most cases, breeding material originating from international nurseries showed higher resistance to LR. Nine Lr genes, viz. Lr9, Lr10, Lr19, Lr26, Lr28, Lr34, Lr37, Lr46, and Lr68, either singly or in combination, were identified in 47 genotypes. Known Lr genes were not detected in the remaining 23 genotypes. The most commonly identified resistance genes were Lr37 (17 cultivars), Lr34 (16 cultivars), and Lr46 (10 cultivars), while Lr19, Lr68, Lr26, and Lr28 were the least frequent. Four Lr genes were identified in Keremet and Hisorok, followed by three Lr genes in Aliya, Rasad, Reke, Mataj, Egana and Almaly/Obri. The molecular screening revealed twenty-nine carriers of a single Lr gene, ten carriers of two genes, six carriers of three genes, and two carriers of four genes. Most of these accessions showed a high and moderate level of APR (Adult plant resistance) and may be utilized for the incorporation of Lr genes in well-adapted wheat cultivars. The most effective combination was Lr37, Lr34, and Lr68, the carriers of which were characterized by a low disease susceptibility index. The obtained results will facilitate breeding programs for wheat resistance in Kazakhstan.

Identification of Stripe Rust Resistance Genes in Common Wheat Cultivars and Breeding Lines from Kazakhstan.

Stripe (yellow) rust, caused by Puccinia striiformis f.sp. tritici (Pst), is a fungal disease that presents one of the most serious threats to the wheat crops, causing severe yield losses worldwide, including Kazakhstan. The objectives of this study were to: (1) evaluate a winter wheat collection for stripe rust resistance during an adult plant growth stage, (2) identify the presence of selected Yr genes using linked molecular markers in wheat germplasm, (3) identify potentially useful resistant wheat genotypes among leading cultivars and advanced breeding lines. This study evaluated 70 winter wheat genotypes for stripe rust resistance. According to the field reactions, 42 entries (60%) had R or MR reactions including 27 breeding lines (38.6%) and 15 (21.4%) cultivars. Twenty-eight breeding lines/cultivars (40.0%) were susceptible in both years. According to the average coefficient of infection value (ACI) six genotypes were regarded as possessing high level of adult plant resistance. Cultivars/lines carrying Yr10 alone or in combination with other Yr resistance genes provided resistance to stripe rust. Eleven breeding lines showed <5% disease severity in both years. Linked marker analysis revealed the presence of several gene and gene complexes (Yr5, Yr10, Yr15, Yr17/Lr37/Sr38 and Yr18/Lr34). Among a collection of 70 winter wheat breeding lines and cultivars produced in Kazakhstan three stripe rust resistance genes (Yr10, Yr5 and Yr15) demonstrated high frequency occurrence (31.4%, 14.0% and 7.0%, respectively). The most abundant was gene Yr10 identified in 22 genotypes. It was followed by the Yr5 gene, which conferred resistance in 14 lines (20%) and Yr18 gene-11 lines (15.7%). Yr15 was identified in 7 genotypes. Yr17/Lr37/Sr38 gene complex was found in 2 entries. Among 70 evaluated germplasm sources, 42 disease resistant entries are potentially useful resistant wheat genotypes. These carriers of different Yr genes can be used directly in breeding programs to improve stripe rust resistance of winter wheat. Marker-assisted selection can be efficiently applied to develop wheat cultivars with effective gene combinations that would directly assist in developing durable resistance in Kazakhstan.

A pictorial disease assessment scale for assessing wheat stripe rust at adult plant growth stage

A pictorial disease assessment scale for assessing wheat stripe rust at adult plant growth stage

Seedling and Adult Plant Resistance in the Ethiopian Bread Wheat Landraces to Stripe Rust Disease

High yielding farmers&amp;rsquo; bread wheat cultivars are threatened by emerging race(s) of stripe (yellow) rust caused by Puccinia striiformis f.sp. tritici (Pst) in the highlands of Ethiopia. In depletion of rust resistance in commercial cultivars, researchers often look for new sources from close relatives and landraces. The objective of this study was to determine stripe rust resistance in selected Ethiopian bread wheat landraces obtained from the Ethiopian Institute of Biodiversity (IBCE). In 2017, a total of 152 accessions were exposed to the prevailing stripe rust races in hot spot areas (Kulumsa and Meraro) in Arsi zone of Oromia region. In the second year (2018), only promising landraces (57) were evaluated both at seedling and adult plant growth stages. The seedling test was conducted in the greenhouse at Kulumsa research center using three (PstS2 (v32), (PstS11) and (PstS11 v25) Pst races. In field evaluations, terminal severity (TRS), coefficient of infection (CI), area under disease progress curve (AUDPC), disease progress rate (DPR) and head infection (HI) were considred. High disease pressure was noted with 100% severity on susceptible entries at both locations and seasons. Highly significant (P&amp;lt;0.001) differences were noted among the landraces for all disease parameters indicated above. Of the 152 landraces, 57(38%) exhibited lower or equal disease reaction compared to the resistant check(Enkoy) across locations. Overall, 18 accessions showed resistance to the prevailing Pst races both at seedling stage and field conditions whereas14 exhibited susceptible /intermediate reaction at seedling stage, but had lower disease reaction under field conditions. This study has identified potential sources of overall and adult plant resistance in the Ethiopian bread wheat landraces to the prevailing Pst races. The authors recommend further studies to determine the diversity and/or novelity of resistance genes in selected accessions. Future wheat improvement should focus on utilization of these genetic resources to minimize the re-current outbreak of rust diseases.

Mapping of a QTL with major effect on reducing leaf rust severity at the adult plant growth stage on chromosome 2BL in wheat landrace Hongmazha.

A major QTL (QLr.cau-2BL) for APR to leaf rust was detected on 2BL; an SSR marker was developed to closely link with QLr.cau-2BL and validated for effectiveness of MAS. The wheat landrace Hongmazha (HMZ) possesses adult plant resistance (APR) to leaf rust. To detect and validate quantitative trait locus (QTL) for the APR, four wheat populations were assessed for leaf rust severity in a total of eight field and greenhouse experiments. The mapping population Aquileja × HMZ (120 recombinant inbred lines, RILs) was genotyped using 90K SNP markers. A major QTL (QLr.cau-2BL) was detected between the markers IWB3854 and IWB21922 on chromosome 2BL. IWB3854 and IWB21922 were positioned at approximately 531.14Mb and 616.48Mb, respectively, on 2BL of IWGSC RefSeq v1.0 physical map. Based on the sequences between 531.14 and 616.48Mb on 2BL of IWGSC RefSeq v1.0, 415 simple sequence repeat (SSR) markers were developed. These markers and 28 previously published SSR makers were screened; the resulted polymorphic markers were used to genotype the relatively larger population RL6058 × HMZ (371 RILs). QLr.cau-2BL was mapped within a 1.5cM interval on 2BL map of RL6058 × HMZ, and a marker (Ta2BL_ssr7) was identified to closely link with QLr.cau-2BL. Effectiveness of selection for QLr.cau-2BL based on Ta2BL_ssr7 was validated using two populations (RL6058 × HMZ F2:3 and Jimai22 × HMZ BC4F2:3). In addition, polymorphism at Ta2BL_ssr7 was detected among a panel of 282 commercial wheat cultivars. We believe, therefore, that Ta2BL_ssr7 should be useful for introducing QLr.cau-2BL into commercial wheat cultivars and for accumulating QLr.cau-2BL with other APR QTL.

Identification of Stripe Rust (Puccinia striiformis F. sp. Tritici) Resistance in the Ethiopian Wheat Landraces

Stripe rust is caused by Puccinia striiformis f. sp. tritici (Pst) is threatening wheat production in Ethiopia. Wheat varieties succumb to new Pst race (s) soon after their release from research centers. The objective of this study was to determine stripe rust resistance in selected Ethiopian wheat landraces obtained from the Ethiopian Institute of Biodiversity (IBCE). In 2017, a total of 197 accessions (152 bread and 45 durum wheat land-races) were exposed to the prevailing stripe rust races in hot spot areas (Kulumsa and Meraro) in Arsi zone of Oromia region. In the second year 2018, only promising landraces 103 (69 bread and 34 durum)) were evaluated both at seedling and adult plant growth stages. The seedling test was conducted in the greenhouse at Kulumsa research center using three Pstraces. In field evaluations, terminal severity (TRS), coefficient of infection (CI), area under disease progress curve (AUDPC), disease progress rate (DPR) and spike infection (SI) were considered. High disease pressure was noted with 100% severity on susceptible entries at both locations and seasons. Highly significant (P<0.001) differences were noted among the landraces for all disease parameters indicated above. Of the 103 landraces, 57 (55%) exhibited lower or equal disease reaction compared to the resistant check (Enkoy) across locations and seasons. Thirty two landraces showed both adult plant and seedling resistance. The 103 Ethiopian wheat landraces that showed field resistance further exposed to three Pst races at seedling stage and 61 exhibited seedling resistance to all races. This study has identified potential sources of seedling and adult plant resistance in the Ethiopian wheat landraces to the prevailing Pst races. Future wheat improvement should focus on utilization of these genetic resources to minimize the re-current outbreak of rust diseases.

QTL Mapping for Seedling and Adult Plant Resistance to Leaf and Stem Rusts in Pamyati Azieva × Paragon Mapping Population of Bread Wheat

Leaf rust (LR) and stem rust (SR) pose serious challenges to wheat production in Kazakhstan. In recent years, the susceptibility of local wheat cultivars has substantially decreased grain yield and quality. Therefore, local breeding projects must be adjusted toward the improvement of LR and SR disease resistances, including genetic approaches. In this study, a spring wheat segregating population of Pamyati Azieva (PA) × Paragon (Par), consisting of 98 recombinant inbred lines (RILs), was analyzed for the resistance to LR and SR at the seedling and adult plant-growth stages. In total, 24 quantitative trait loci (QTLs) for resistance to rust diseases at the seedling and adult plant stages were identified, including 11 QTLs for LR and 13 QTLs for SR resistances. Fourteen QTLs were in similar locations to QTLs and major genes detected in previous linkage mapping and genome-wide association studies. The remaining 10 QTLs are potentially new genetic factors for LR and SR resistance in wheat. Overall, the QTLs revealed in this study may play an important role in the improvement of wheat resistance to LR and SR per the marker-assisted selection approach.

Susceptibility of Winter Wheat and Triticale to Yellow Rust Influenced by Complex Interactions between Vernalisation, Temperature, Plant Growth Stage and Pathogen Race

Environmental factors influence the disease susceptibility of crop plants. In this study, we established an experimental system to investigate the effects of vernalisation, temperature and plant growth stage on the susceptibility of winter wheat and winter triticale to Puccinia striiformis, the causal agent of yellow (stripe) rust. Two temperature regimes: standard (18 °C day/12 °C night) and low (12 °C day/6 °C night), vernalised and non-vernalised seedlings, vernalised adult plants and two pathogen races were investigated. At low temperatures, vernalisation reduced the susceptibility of seedlings exposed to the ‘Warrior’ race, while this was only the case for five out of eight varieties exposed to the ‘Kranich’ race. Changing from standard to low temperature resulted in increased susceptibility of non-vernalised seedlings of seven varieties inoculated with the ‘Warrior’ race and five varieties inoculated with the ‘Kranich’ race. Increased susceptibility at low temperature was also detected for several varieties at the adult plant growth stage. Comparisons between vernalised seedlings and adult plants revealed an effect of plant growth stage on disease susceptibility (e.g., Adult Plant Resistance) in five varieties at standard temperature for the ‘Warrior’ race and in five and four varieties at standard and low temperature respectively, for the ‘Kranich’ race. The complex and unpredictable interactions between environment and pathogen influencing yellow rust susceptibility of individual varieties stress the importance of phenotyping for disease resistance under different environmental conditions and pathogen populations. The environmental impact on rust susceptibility should also be taken into account in early-warning systems targeting wheat and triticale breeding programmes and growers.

Identification of a major QTL on chromosome arm 2AL for reducing yellow rust severity from a Chinese wheat landrace with evidence for durable resistance.

A QTL on 2AL for reducing yellow rust severity was identified from a Chinese wheat landrace, being more effective than Yr18, with evidence for durable resistance from field observations. Utilization of wheat resistance is an important strategy to control yellow rust. The Chinese wheat landrace Hong Qimai (HQM) and the advanced breeding line AQ24788-83 (AQ; a progeny of HQM) can significantly reduce disease severity at the adult-plant growth stage. HQM has maintained adult-plant resistance for a prolonged period of time. To study the inheritance of the resistance, 126 recombinant inbred lines (RILs) derived from the cross Thatcher (TC) × HQM and 138 RILs from Luke × AQ were assessed for disease severity in six field trials. A genetic map of TC × HQM was constructed by genotyping these RILs using the 90K wheat single-nucleotide polymorphism chip. Luke × AQ map was previously constructed for another disease study and also utilized here. Based on these maps and disease data, a quantitative trait locus (QTL) was detected on the chromosome arm 2AL from both TC × HQM and Luke × AQ and designated as QYr.cau-2AL. The resistance allele at QYr.cau-2AL came from HQM and AQ. QYr.cau-2AL was significantly effective across all the test environments and different genetic backgrounds, with its effect magnitude being higher than that of Yr18. QYr.cau-2AL synergistically acted with Yr18 and a QTL for high-temperature adult-plant resistance on 2BS, resulting in an elevated resistance from the juvenile plant growth stage onward, although QYr.cau-2AL alone displayed no substantial resistance at juvenile stage. Evidence indicates that QYr.cau-2AL is novel and confers durable resistance, and thus, should have high potential value for practical breeding.

Unlocking new alleles for leaf rust resistance in the Vavilov wheat collection.

Thirteen potentially new leaf rust resistance loci were identified in a Vavilov wheat diversity panel. We demonstrated the potential of allele stacking to strengthen resistance against this important pathogen. Leaf rust (LR) caused by Puccinia triticina is an important disease of wheat (Triticum aestivum L.), and the deployment of genetically resistant cultivars is the most viable strategy to minimise yield losses. In this study, we evaluated a diversity panel of 295 bread wheat accessions from the N. I. Vavilov Institute of Plant Genetic Resources (St Petersburg, Russia) for LR resistance and performed genome-wide association studies (GWAS) using 10,748 polymorphic DArT-seq markers. The diversity panel was evaluated at seedling and adult plant growth stages using three P. triticina pathotypes prevalent in Australia. GWAS was applied to 11 phenotypic data sets which identified a total of 52 significant marker-trait associations representing 31 quantitative trait loci (QTL). Among them, 29 QTL were associated with adult plant resistance (APR). Of the 31 QTL, 13 were considered potentially new loci, whereas 4 co-located with previously catalogued Lr genes and 14 aligned to regions reported in other GWAS and genomic prediction studies. One seedling LR resistance QTL located on chromosome 3A showed pronounced levels of linkage disequilibrium among markers (r 2=0.7), suggested a high allelic fixation. Subsequent haplotype analysis for this region found seven haplotype variants, of which two were strongly associated with LR resistance at seedling stage. Similarly, analysis of an APR QTL on chromosome 7B revealed 22 variants, of which 4 were associated with resistance atthe adult plant stage. Furthermore, most of the tested lines in the diversity panel carried 10 or more combined resistance-associated marker alleles, highlighting the potential of allele stacking for long-lasting resistance.

Identification of Leaf Rust Resistance Genes in Chinese Common Wheat Cultivars.

Puccinia triticina Eriks. (Pt), the causal agent of wheat (Triticum aestivum L.) leaf rust, is the most widespread disease of common wheat worldwide. In the present study, 83 wheat cultivars from three provinces of China and 36 tester lines with known leaf rust resistance (Lr) genes were inoculated in the greenhouse with 18 Pt pathotypes to identify seedling effective Lr genes. Field tests were also performed to characterize slow leaf rusting responses at the adult plant growth stage in Baoding and Zhoukou in the 2014-15 and 2015-16 cropping seasons. Twelve Lr genes, viz. Lr1, Lr26, Lr3ka, Lr11, Lr10, Lr2b, Lr13, Lr21, Lr34, Lr37, Lr44, and Lr46 either singly or in combination were identified in 41 cultivars. Known Lr genes were not detected in the remaining 42 cultivars. The most commonly identified resistance genes were Lr26 (20 cultivars), Lr46 (18 cultivars), and Lr1 (eight cultivars). Less frequently detected genes included Lr13, Lr34, and Lr37 (each present in four cultivars), Lr10 (three cultivars), and Lr3ka and Lr44 (each in two cultivars). Evidence for the presence of genes Lr11, Lr2b, and Lr21 (each in one cultivar) was also obtained. Seventeen cultivars were found to have slow rusting resistance in both field growing seasons.

English

Barley nurseries comprising 820 lines with 479 unique pedigrees sourced from the International Centre for Agricultural Research in the Dry Areas (ICARDA) were screened for seedling and adult plant resistance (APR) against Australian isolates of barley leaf rust pathogen Puccinia hordei Otth. Ninety three percent of the lines were postulated to carry the seedling leaf rust resistance gene Rph3 based on their susceptibility in the greenhouse and field against Rph3 virulent pathotype and resistance to Rph3 avirulent pathotypes. The remaining lines showed either presence of uncharacterised seedling resistance (1%) and uncharacterised APR (1%). Five percent of lines were susceptible at both seedling and adult plant growth stages. Of the six lines identified to carry uncharacterised APR, three likely carried Rph20 based on the presence of the Rph20-linked marker bPb-0837. The results suggested that most of the ICARDA germplasm tested is not suitable for leaf rust resistance in Australia due to the presence of virulence for Rph3. Lines carrying uncharacterised seedling resistance and APR are potentially new sources of resistance, and are recommended for genetic analysis. Key words: Hordeum vulgare, Puccinia hordei, adult plant resistance, Rph3.

Genome-wide DArT and SNP scan for QTL associated with resistance to stripe rust (Puccinia striiformis f. sp. tritici) in elite ICARDA wheat (Triticum aestivum L.) germplasm.

Identified DArT and SNP markers including a first reported QTL on 3AS, validated large effect APR on 3BS. The different genes can be used to incorporate stripe resistance in cultivated varieties. Stripe rust [yellow rust, caused by Puccinia striiformis f. sp. tritici (Pst)] is a serious disease in wheat (Triticum aestivum). This study employed genome-wide association mapping (GWAM) to identify markers linked to stripe rust resistance genes using Diversity Arrays Technology (DArT(®)) and single-nucleotide polymorphism (SNP) Infinium 9K assays in 200 ICARDA wheat genotypes, phenotyped for seedling and adult plant resistance in two sites over two growing seasons in Syria. Only 25.8% of the genotypes showed resistance at seedling stage while about 33 and 44% showed moderate resistance and resistance response, respectively. Mixed-linear model adjusted for false discovery rate at p<0.05 identified 12 DArT and 29 SNP markers on chromosome arms 3AS, 3AL, 1AL, 2AL, 2BS, 2BL, 3BS, 3BL, 5BL, 6AL, and 7DS significantly linked to Pst resistance genes. Of these, the locus on 3AS has not been previously reported to confer resistance to stripe rust in wheat. The QTL on 3AS, 3AL, 1AL, 2AL, and 2BS were effective at seedling and adult plant growth stages while those on 3BS, 3BL, 5BL, 6AL and 7DS were effective at adult plant stage. The 3BS QTL was validated in Cham-6×Cham-8 recombinant inbred line population; composite interval analysis identified a stripe resistance QTL flanked by the DArT marker, wPt-798970, contributed by Cham-6 parent which accounted for 31.2% of the phenotypic variation. The DArT marker "wPt-798970" lies 1.6cM away from the 3BS QTL detected within GWAM. Epistatic interactions were also investigated; only the QTL on 1AL, 3AS and 6AL exhibited interactions with other loci. These results suggest that GWAM can be an effective approach for identifying and improving resistance to stripe rust in wheat.

Spot form of net blotch resistance in barley is under complex genetic control.

Evaluation of resistance to Pyrenophora teres f. maculata in barley breeding populations via association mapping revealed a complex genetic architecture comprising a mixture of major and minor effect genes. In the search for stable resistance to spot form of net blotch (Pyrenophora teres f. maculata, SFNB), association mapping was conducted on four independent barley (Hordeum vulgare L.) breeding populations comprising a total of 898 unique elite breeding lines from the Northern Region Barley Breeding Program in Australia for discovery of quantitative trait loci (QTL) influencing resistance at seedling and adult plant growth stages. A total of 29 significant QTL were validated across multiple breeding populations, with 22 conferring resistance at both seedling and adult plant growth stages. The remaining 7 QTL conferred resistance at either seedling (2 QTL) or adult plant (5 QTL) growth stages only. These 29 QTL represented 24 unique genomic regions, of which five were found to co-locate with previously identified QTL for SFNB. The results indicated that SFNB resistance is controlled by a large number of QTL varying in effect size with large effects QTL on chromosome 7H. A large proportion of the QTL acted in the same direction for both seedling and adult responses, suggesting that phenotypic selection for SFNB resistance performed at either growth stage could achieve adequate levels of resistance. However, the accumulation of specific resistance alleles on several chromosomes must be considered in molecular breeding selection strategies.

Evaluation of Bread Wheat Varieties to Dominant Races of Stem Rust (&amp;lt;i&amp;gt;Puccinia graminis f. sp. Tritici&amp;lt;/i&amp;gt;) Pathogen

Stem rust (Black rust) caused by Puccinia graminis f. sp. tritici is one of the most important air borne diseases of wheat (Triticum aestivum) in the central high lands of Ethiopia, including west and southwest Shewa zones. The pathogen is capable to produce new physiological races that attack resistant varieties and develop epidemic under optimal environmental conditions which results in a serious yield loss. However, information on the reaction of bread wheat varieties to dominant races in west and southwest Shewa zones is lacking. Therefore, the present study was conducted to evaluate the reaction of 12 commonly grown bread wheat varieties by artificial inoculation against the major virulent races at seedling stage in green house (TKTTF and TTKSK) and at adult plant growth stage under field condition (TTKSK). In the green house test, varieties Huluka and Ogena showed resistance to TTKSK and TKTTF races. Likewise, the two varieties showed moderately resistance reaction at adult plant growth stage with terminal severity of below 10%. Whereas, ET-13A2 was susceptible to both races at both plant growth stages. Digalu was susceptible to TKTTF, but resistant to TTKSK at seedling stage, and under field condition it showed severity of 63.3S. The lowest mean AUDPC was recorded on the Ogena, Huluka and Shorima varieties with 37, 52.7 and 103.7 values in the mentioned order. In contrast, the highest mean AUDPC of 1225 on Morocco and 805.8 on Digalu were recorded. Similarly, the maximum mean disease infection rate was also recorded on Morocco and Digalu varieties. Hence, varieties Ogena and Huluka that showed resistance to both virulent races at seedling and adult plant growth stages can be used as sources of resistance in wheat breeding program.

Characterising seedling and adult plant resistance to Puccinia hordei in Hordeum vulgare

AbstractA set of 113 genotypes of barley (Hordeum vulgare subsp. vulgare), along with the susceptible control genotype Gus, was tested for response to the barley leaf rust pathogen Puccinia hordei in the greenhouse (as seedlings) and field (as adult plants). The tests revealed that 68 lines carried adult plant resistance (APR), 23 lines carried uncharacterised seedling resistance (USR) and that three lines carried the seedling resistance gene Rph3. Nineteen lines lacked detectable seedling resistance and were also susceptible in the field at adult plant growth stages. The presence of marker bPb‐0837, linked to the APR gene Rph20, in 35 of the 68 lines carrying APR, suggested they carry this gene. The remaining 33 lines, which lacked the Rph20 linked marker, are likely sources of new uncharacterised APR. Pedigree analysis of the 68 lines found to carry APR revealed that 32 were related to cv. Gull and to Hordeum laevigatum; two were related to cv. Bavaria and one related to cvv. Manchuria and Taganrog, suggesting that these genotypes may be the ancestral sources of the APR carried by each.

Response of Improved Durum Wheat (Triticum durum L.) Varieties to Wheat Stem Rust in Central Ethiopia

Wheat stem rust caused by Puccinia graminis f.sp. tritici is amongst the biotic factors which causes up to 100% yield loss during epidemic years. Therefore, the present study was carried out to observe the reaction of improved durum wheat varieties to virulent stem rust isolates at seedling growth stage and to stem rust population at adult growth stages. The finding of this experimental study was based on isolation and multiplication of virulent races of P. graminis, then ten durum wheat varieties including the susceptible check morocco were tested for the virulent isolates at seedling growth stage; and the reaction of these varieties under natural field conditions were evaluated in the Eastern and Western Showa of Central Ethiopia at adult growth stages. At seedling growth stage, 60% of varieties tested with the virulent stem rust isolate from Debrezeit exhibited resistance, while all varieties were resistant to Ambo isolate. Ten durum wheat varieties evaluated at adult plant growth stage to stem rust population of Debrezeit (Eastern Showa) showed severities of 20S in the variety Geredo to 70S in the variety Foka, while at Ambo (Western Showa) only the susceptible check, Morocco was infected up to 20S. The result indicated that stem rust from Debrezeit was virulent to durum wheat varieties as compared to the Ambo population.

Mapping of QTL conferring resistance to sharp eyespot (Rhizoctonia cerealis) in bread wheat at the adult plant growth stage

Seven sharp eyespot resistance QTL were detected consistently across five environments and delimited to seven DNA marker intervals, respectively, six of which were independent of plant height and heading time. Sharp eyespot, caused mainly by the soil-borne fungus Rhizoctonia cerealis, is one of the important diseases of bread wheat (Triticum aestivum L.). This disease has escalated into a major threat to wheat production in some regions of the world. Wheat resistance to sharp eyespot can be a potential means to reduce the needs for application of fungicides and agricultural inputs. In the present study, the winter wheat lines, Luke and AQ24788-83, both of which possess quantitative resistance to sharp eyespot, were crossed and a population consisting 241 recombinant-inbred lines (RILs) was constructed. These RILs were assessed for sharp eyespot resistance by conducting five field and greenhouse trials during the period from 2008 to 2012, and they were genotyped with 549 simple-sequence repeat DNA markers. Seven quantitative trait loci (QTL) were detected consistently across the five trial environments to be associated with the sharp eyespot resistance. They were mapped on chromosomes 1A, 2B, 3B, 4A, 5D, 6B, and 7B. Four of these QTL are unequivocally novel, while it is possible that the other three might also be novel. Plant height and heading date of the 241 RILs were recorded in the four field trials. All of the seven disease resistance QTL were independent of plant height and heading time except one that was significantly associated with plant heading time. This association might be attributed genetically to a single QTL, or to different but closely linked QTL. In the case of single QTL, pleiotropism might be involved or the sharp eyespot resistance might be conferred in a physical instead of physiological nature.

Identification and characterization of seedling and adult plant resistance to Puccinia hordei in Chinese barley germplasm

AbstractLeaf rust of barley, caused by Puccinia hordei, occurs in all barley‐growing regions of Australia causing significant yield losses under epidemic conditions. The development and use of resistant cultivars are the most economical and environmentally sustainable method to control leaf rust which in turn relies on ongoing efforts to identify and characterize new sources of resistance. The aim of this study was to postulate known genes and/or identify new sources of resistance to P. hordei. Fifty‐two genotypes were assessed at the seedling and adult plant growth stages. On the basis of multipathotype tests, 39 genotypes lacked detectable seedling resistance, and nine were postulated to carry the genes Rph2, Rph4, Rph12 and Rph19 singly. Four genotypes carried uncharacterized seedling resistance; however, the gene(s) present in each were ineffective to at least one of the pathotypes used. Field tests at the adult plant growth stage revealed the presence of adult plant resistance (APR) in 12 genotypes. Tests of allelism and marker analysis indicated that resistance genes present in these genotypes were independent of the APR gene Rph20.