Breeding Wheat for Powdery Mildew Resistance: Genetic Resources and Methodologies-A Review

Powdery mildew (PM) of wheat caused by Blumeria graminis f. sp. tritici is among the most important wheat diseases, causing significant yield and quality losses in many countries worldwide. Considerable progress has been made in resistance breeding to mitigate powdery mildew. Genetic host resistance employs either race-specific (qualitative) resistance, race-non-specific (quantitative), or a combination of both. Over recent decades, efforts to identify host resistance traits to powdery mildew have led to the discovery of over 240 genes and quantitative trait loci (QTLs) across all 21 wheat chromosomes. Sources of PM resistance in wheat include landraces, synthetic, cultivated, and wild species. The resistance identified in various genetic resources is transferred to the elite genetic background of a well-adapted cultivar with minimum linkage drag using advanced breeding and selection approaches. In this effort, wheat landraces have emerged as an important source of allelic and genetic diversity, which is highly valuable for developing new PM-resistant cultivars. However, most landraces have not been characterized for PM resistance, limiting their use in breeding programs. PM resistance is a polygenic trait; therefore, the degree of such resistance is mostly influenced by environmental conditions. Another challenge in breeding for PM resistance has been the lack of consistent disease pressure in multi-environment trials, which compromises phenotypic selection efficiency. It is therefore imperative to complement conventional breeding technologies with molecular breeding to improve selection efficiency. High-throughput genotyping techniques, based on chip array or sequencing, have increased the capacity to identify the genetic basis of PM resistance. However, developing PM-resistant cultivars is still challenging, and there is a need to harness the potential of new approaches to accelerate breeding progress. The main objective of this review is to describe the status of breeding for powdery mildew resistance, as well as the latest discoveries that offer novel ways to achieve durable PM resistance. Major topics discussed in the review include the genetic basis of PM resistance in wheat, available genetic resources for race-specific and adult-plant resistance to PM, important gene banks, and conventional and complimentary molecular breeding approaches, with an emphasis on marker-assisted selection (MAS)

Bread wheat cultivar Popo harbors QTLs for seedling and adult plant resistance to leaf rust in South African and Argentine environments

Leaf rust, caused by the fungus Puccinia triticina Eriks (Pt), is a destructive disease affecting wheat (Triticum aestivum L.) production in many countries, and a serious threat to food security. As a result, several breeding programs have included leaf rust resistance as an important trait. The discovery and identification of new resistance genes that could aid in incorporating durable or long-lasting leaf rust resistance into wheat is fundamental in these breeding programs. The present study aimed to identify quantitative trait loci (QTLs) for leaf rust resistance in 127 recombinant inbred lines (RIL) developed from the cross between the resistant wheat cultivar Popo and the susceptible cultivar Kariega. The RIL population and parental lines were phenotyped for leaf rust infection type and severity at seedling and adult plant stage, respectively. The former in the greenhouse (in Argentina) and the latter in multiple field test environments comprising 3 locations in South Africa (in Tygerhoek in the Western Cape Province during the 2014, 2015, 2017 and 2018 cropping seasons; Clarens during 2014, 2016 and 2017 cropping seasons and in Bethlehem in the Free State Province during 2017 cropping season) and in 1 location in Argentina (during the 2017 and 2018 cropping seasons in Marcos Juárez, Córdoba Province). The population was genotyped using genotyping-by-sequencing. A total of 12,080 silicoDArT and 2,669 SNP markers were used for QTL analysis. In total, 25 putative QTLs for resistance to leaf rust at seedling and adult plant stages were identified, including 5 QTLs for seedling and 20 QTLs for adult plant resistance (APR). Interestingly, both Popo and Kariega contributed with alleles for resistance. Significant loci for reducing leaf rust infection at seedling stage were designated QLr.arc-1A, QLr.arc-2B, QLr.arc-5B, QLr.arc-6A and QLr.arc-6D. Three minor QTLs derived from Popo designated as QLr.arc-1B1, QLr.arc-2D and QLr.arc-3D were also detected from the field tests, explaining 5–10%, 10–16% and 5–7% of the phenotypic variance, respectively. The identified QTLs and their closely linked silicoDArT and SNP-based markers can be used for fine mapping and candidate gene discovery in wheat breeding programs targeting durable leaf rust resistance.Fil: Figlan, Sandiswa. University of South Africa; SudáfricaFil: Hlongoane, Tsepiso. No especifíca;Fil: Bainotti, Carlos Tomas. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Córdoba. Estación Experimental Agropecuaria Marcos Juárez; ArgentinaFil: Campos, Pablo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Bordenave; ArgentinaFil: Vanzetti, Leonardo Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Córdoba. Estación Experimental Agropecuaria Marcos Juárez; ArgentinaFil: Tranquilli, Gabriela Edith. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Tsilo, Toi John. University of South Africa; Sudáfric

Genome mapping of end-use quality traits in a wheat recombinant inbred population.

University of Minnesota Ph.D. dissertation. December 2009. Major: Applied Plant Sciences. Advisor: Prof James A Anderson. 1 computer file (PDF); xv, 175 pages, appendices 1-III. Ill. (some col.)Development of high performing wheat cultivars, with high grain yield and end-use quality, is a major focus in wheat breeding programs worldwide. The main objective of the study was to identify chromosome regions harboring genes that influence end-use quality traits in hard red spring wheat lines. Agronomic traits, kernel characteristics, milling related traits, dough mixing strength, and bread-making properties were evaluated from a population of 139 recombinant inbred lines (RILs), two parental lines, and three check varieties grown at three Minnesota locations in 2006. Whole genome genetic linkage maps showing quantitative trait loci (QTL) were constructed. Genetic maps contained 531 SSR and DArT marker loci and covered all 21 chromosomes of wheat. Flanking markers were identified for the stem rust resistance gene Sr6 on chromosome 2D. Stable QTL clusters influencing kernel characteristics were identified on chromosome 2A, 5B, and 7A. Of the twenty-eight QTL that influenced milling properties, QTL clusters were identified on six chromosomes: 1A, 1B, 5A, 5B, 5D, and 7B. Six QTL were identified for endosperm texture, with the main QTL on chromosomes 1A, 5A and 5D. Eleven chromosome regions were associated with endosperm polymeric proteins. Forty-three QTL influenced dough-mixing strength and bread-making properties. DNA markers linked to these QTL will provide opportunity for increasing the frequency of desirable alleles through marker-assisted selection

Response of Bread Wheat Genotypes for Drought and Low Nitrogen Stress Tolerance

Drought stress and nitrogen (N) deficiency are the major causes of yield losses in bread wheat (Triticum aestivum) production. Breeding wheat cultivars with combined drought and low N stress tolerance is an economical approach for yield gains. The objective of this study was to evaluate the response of diverse bread wheat genotypes under drought and low N stress conditions to select high-performing genotypes for developing breeding populations and production to mitigate against drought and low N stress. Fifty bread wheat genotypes were evaluated under drought-stressed (DS) and non-stressed (NS) conditions and N application rates of 50, 100 and 200 kg N ha−1. The experiments were conducted in a controlled environment and field conditions during the 2019/20 cropping season. Data on grain yield and yield components were collected and subjected to statistical analysis. The four-way interaction involving genotype, water regime, N treatments and testing environment had a significant (p −1 reduced grain yield by 20% compared to NS and 50 kg N ha−1. The grain yield ranged from 120 to 337 g/m2, with a mean of 228 g/m2 under DS. Under DS and 200 kg N ha−1, the genotype designated as SBO 19 had a higher grain yield of 337 g/m2, followed by SBO 22 (335 g/m2), SBO 16 (335 g/m2), SBO 04 (335 g/m2) and SBO 33 (335 g/m2). Grain yields under DS and 50 kg N ha−1, and NS and 50 kg N ha−1 had a positive and significant correlation (r > 0.5; p < 0.01) with most of the evaluated traits. Highly correlated traits directly contribute to total yield gain and should be incorporated during the selection of high-yielding genotypes. The study identified the 10 best lines that are high-yielding with early flowering and maturity under DS or NS conditions and the three N treatments. The selected lines are recommended as breeding parents to develop drought-adapted and N-use efficient genetic resources. The identified genotypes are important for sustainable wheat production and effective breeding of improved cultivars to mitigate drought stress and soil nutrient deficiencies, to ensure food security in Sub-Saharan Africa

Response of Bread Wheat Genotypes for Drought and Low Nitrogen Stress Tolerance

Drought stress and nitrogen (N) deficiency are the major causes of yield losses in bread wheat (Triticum aestivum) production. Breeding wheat cultivars with combined drought and low N stress tolerance is an economical approach for yield gains. The objective of this study was to evaluate the response of diverse bread wheat genotypes under drought and low N stress conditions to select high-performing genotypes for developing breeding populations and production to mitigate against drought and low N stress. Fifty bread wheat genotypes were evaluated under drought-stressed (DS) and non-stressed (NS) conditions and N application rates of 50, 100 and 200 kg N ha&minus;1. The experiments were conducted in a controlled environment and field conditions during the 2019/20 cropping season. Data on grain yield and yield components were collected and subjected to statistical analysis. The four-way interaction involving genotype, water regime, N treatments and testing environment had a significant (p &lt; 0.05) effect on all assessed agronomic traits, suggesting that genotype response depended on the treatment combinations. Drought stress and 50 kg N ha&minus;1 reduced grain yield by 20% compared to NS and 50 kg N ha&minus;1. The grain yield ranged from 120 to 337 g/m2, with a mean of 228 g/m2 under DS. Under DS and 200 kg N ha&minus;1, the genotype designated as SBO 19 had a higher grain yield of 337 g/m2, followed by SBO 22 (335 g/m2), SBO 16 (335 g/m2), SBO 04 (335 g/m2) and SBO 33 (335 g/m2). Grain yields under DS and 50 kg N ha&minus;1, and NS and 50 kg N ha&minus;1 had a positive and significant correlation (r &gt; 0.5; p &lt; 0.01) with most of the evaluated traits. Highly correlated traits directly contribute to total yield gain and should be incorporated during the selection of high-yielding genotypes. The study identified the 10 best lines that are high-yielding with early flowering and maturity under DS or NS conditions and the three N treatments. The selected lines are recommended as breeding parents to develop drought-adapted and N-use efficient genetic resources. The identified genotypes are important for sustainable wheat production and effective breeding of improved cultivars to mitigate drought stress and soil nutrient deficiencies, to ensure food security in Sub-Saharan Africa

Genetic Improvement of Wheat for Drought Tolerance: Progress, Challenges and Opportunities

Wheat production and productivity are challenged by recurrent droughts associated with climate change globally. Drought and heat stress resilient cultivars can alleviate yield loss in marginal production agro-ecologies. The ability of some crop genotypes to thrive and yield in drought conditions is attributable to the inherent genetic variation and environmental adaptation, presenting opportunities to develop drought-tolerant varieties. Understanding the underlying genetic, physiological, biochemical, and environmental mechanisms and their interactions is key critical opportunity for drought tolerance improvement. Therefore, the objective of this review is to document the progress, challenges, and opportunities in breeding for drought tolerance in wheat. The paper outlines the following key aspects: (1) challenges associated with breeding for adaptation to drought-prone environments, (2) opportunities such as genetic variation in wheat for drought tolerance, selection methods, the interplay between above-ground phenotypic traits and root attributes in drought adaptation and drought-responsive attributes and (3) approaches, technologies and innovations in drought tolerance breeding. In the end, the paper summarises genetic gains and perspectives in drought tolerance breeding in wheat. The review will serve as baseline information for wheat breeders and agronomists to guide the development and deployment of drought-adapted and high-performing new-generation wheat varieties

Genomic Regions Influencing Preharvest Sprouting Tolerance in Two Doubled-Haploid Wheat Populations (<i>Triticum aestivum</i> L.)

The current and projected climate change that is represented by increasing temperatures and humidity levels and irregular rainfall patterns promotes the occurrence of preharvest sprouting (PHS) in wheat. PHS results in significant economic losses, globally, which necessitates the need for high-yielding cultivars with increased PHS tolerance; hence, this study was conducted. The current study evaluated two doubled-haploid (DH) wheat populations of Tugela-Dn × Elands and Elands × Flamink across six environments in the Free State Province of South Africa to select genotypes with increased PHS tolerance and further map the underlying loci. Significant effects of DH lines (194) and environments (6) were observed for PHS tolerance. The results of this study validate previous findings that PHS is only expressed when environmental conditions are conducive. Quantitative trait loci (QTL) mapping using single-nucleotide polymorphism (SNP) and silicoDArT markers revealed three additive QTLs with major effects on chromosomes 5B and 7B, and these QTLs were detected more than once, when conditions were favourable. These QTLs explained a phenotypic variation (PVE) varying between 10.08% and 20.30% (LOD = 2.73–3.11). About 16.50% of DH lines performed to the level of Elands (the PHS-tolerant parent) and are recommended for further selection in a pre-breeding or breeding programme. The findings of this study are expected to expedite the on-going breeding efforts for PHS tolerance in winter wheat, which will facilitate the development of PHS-tolerant cultivars adapted to the South African environment

Phenotypic Variation of Sorghum Accessions for Grain Yield and Quality Traits

Millions of people depend on sorghum (Sorghum bicolor (L.) Moench) as a staple food crop. Due to the ever-changing climate, more focus should be placed on sorghum as it can grow in environments that are marginal for maize (Zea mays L.) and other grain crops. Identification of unique accessions with desirable phenotypic variations allow plant breeders to use the accessions as parental material in a breeding program. The objectives of this study were to determine the extent of diversity in sorghum accessions based on grain yield and quality traits, as well as to identify accessions with high grain yield. One hundred sorghum accessions were evaluated at Potchefstroom (South Africa) in two consecutive growing seasons. The experiment was laid out in a 20 × 5 alpha lattice design with three replications. ANOVA showed highly significant (p = 0.01) variation among the accessions for all traits. There was a positive correlation (r = 0.209) between starch and grain yield. Seven high-yielding accessions with high protein and seven accessions with high starch were identified. These accessions could be used for improving yield, protein and starch in the grain. Tannin content ranged from zero to 24.40 mgCE/100 mg; 75 accessions were characterized as type I. Seven accessions were characterized as type II, and 18 accessions were characterized as type III. The 100 sorghum accessions were grouped into five distinct clusters that offer a wide range of phenotypic variation for the traits studied

Establishment and Characterization of Callus and Cell Suspension Cultures of Selected Sorghum bicolor (L.) Moench Varieties: A Resource for Gene Discovery in Plant Stress Biology

Sorghum, a naturally drought tolerant crop, is genetically diverse and provides a wide gene pool for exploitation in crop breeding. In this study, we experimentally assessed friable callus induction rates of seven sorghum varieties using shoot explant for the generation of cell suspension cultures. The cell suspensions were characterized in terms of cell growth and viability profiles as well as gene expression following 400 mM sorbitol-induced osmotic stress for 72 h. Only ICSB 338, a drought susceptible variety, was readily amenable to friable callus formation. Cell culture growth plots of both ICSB 338 and White sorghum (used as a reference line) depicted typical sigmoidal curves. Interestingly, Evans blue assay showed that ICSB 338 cell cultures are more susceptible to osmotic stress than the White sorghum cells. The osmotic stress treatment also triggered differential expression of eight target genes between the two cell culture lines. Overall, these results suggest that the genetic diversity of sorghum germplasm influences friable callus induction rates and molecular responses to osmotic stress, and could be further exploited in plant stress biology studies. Therefore, we have developed a valuable resource for use in molecular studies of sorghum in response to a range of biotic and abiotic stresses

Breeding Wheat for Powdery Mildew Resistance: Genetic Resources and Methodologies—A Review

Powdery mildew (PM) of wheat caused by Blumeria graminis f. sp. tritici is among the most important wheat diseases, causing significant yield and quality losses in many countries worldwide. Considerable progress has been made in resistance breeding to mitigate powdery mildew. Genetic host resistance employs either race-specific (qualitative) resistance, race-non-specific (quantitative), or a combination of both. Over recent decades, efforts to identify host resistance traits to powdery mildew have led to the discovery of over 240 genes and quantitative trait loci (QTLs) across all 21 wheat chromosomes. Sources of PM resistance in wheat include landraces, synthetic, cultivated, and wild species. The resistance identified in various genetic resources is transferred to the elite genetic background of a well-adapted cultivar with minimum linkage drag using advanced breeding and selection approaches. In this effort, wheat landraces have emerged as an important source of allelic and genetic diversity, which is highly valuable for developing new PM-resistant cultivars. However, most landraces have not been characterized for PM resistance, limiting their use in breeding programs. PM resistance is a polygenic trait; therefore, the degree of such resistance is mostly influenced by environmental conditions. Another challenge in breeding for PM resistance has been the lack of consistent disease pressure in multi-environment trials, which compromises phenotypic selection efficiency. It is therefore imperative to complement conventional breeding technologies with molecular breeding to improve selection efficiency. High-throughput genotyping techniques, based on chip array or sequencing, have increased the capacity to identify the genetic basis of PM resistance. However, developing PM-resistant cultivars is still challenging, and there is a need to harness the potential of new approaches to accelerate breeding progress. The main objective of this review is to describe the status of breeding for powdery mildew resistance, as well as the latest discoveries that offer novel ways to achieve durable PM resistance. Major topics discussed in the review include the genetic basis of PM resistance in wheat, available genetic resources for race-specific and adult-plant resistance to PM, important gene banks, and conventional and complimentary molecular breeding approaches, with an emphasis on marker-assisted selection (MAS)