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)

Screening wheat (Triticum aestivum L.) landraces to use as donor lines of Russian wheat aphid resistance and the application of molecular markers to identify potential high yielding genotypes with minimal linkage drag to undesirable traits

Wheat is an important staple food produced, consumed and traded globally. South Africa is now experiencing climate change, the emergence of biotypes and pathotypes, increasing human population, as well as a decrease in wheat production due to farmer’s transition to more profitable crops like maize and soybeans. Improvement of wheat yield, selection of biotype resistant and high yielding cultivars and wheat production increase is important for meeting the demands of increasing population. This study aimed to select genotypes with resistance to the four South African RWA biotypes and with high yield potential. This was done to contribute to the Agricultural Research Council-Small Grain (ARC-SG) RWA resistance breeding and crop improvement program. This was achieved by screening 80 genotypes with the four RWA biotypes to identify genotypes with unique and stable resistance. Furthermore, by phenotyping the growth period, spike related traits, and screening yield component molecular markers on the RWASA3 and RWASA4 highly resistant plants. RWASA3 was the most damaging biotype while RWASA1 was the least damaging biotype (P<0.0001). After phenotyping the donor lines with the four RWA biotypes, 25 sources of resistance to all four biotypes were identified with comparable resistance to the differential check CItr 2401. New resistance sources to these biotypes were thus found and could help in identifying RWASA5 resistance in the future. Seven new and distinctive resistance patterns from RWASA1 to RWASA4 i.e. RRSR, RSRR, RSRS, RSSR, SRSR, SSRR and SRRS were found on 22 genotypes based on resistance to either one or both RWASA3 and RWASA4. These genotypes add to the ARC-SG host plant resistance pre-breeding. Both stable and mixed reaction exists within the landraces, suggesting the need for continuous selection of useful traits. Therefore, when searching for new germplasm source, landraces are recommended. The spike traits measured on selected RWASA3 and RWASA4 genotypes showed direct and indirect influence on each other. Correlation of coefficient showed strong and positive relationships among the spike traits measured. The tested SSR and CAPS markers were informative whereby almost all genotypes had linkage to one gene if not all four of the yield component genes. Their polymorphism has shown that these markers could be used in different genetic backgrounds.Korong sebjalo se se tlwaelegileng lefaseng ka bophara, se angwa gampe ke mabaka a go swana le tše di phelago le tše di sa phelego, maruo le kgolo ya palo ya batho mo Afrika Borwa, ho fokotšega ga mobu o loketšeng temo le temo ya dibjalo tše di nago le poelo e ntši tša go swana le lekgea le dinawa. Ge gole bjalo, go kganya ga semela le temo goba tšhumišo ya korong y abo ba le poelo e tšhi ka ditshenyegelo tša fase go bohlokwa go fihlela ditlhoko tša legae tša korong. Boitutho bjo bo diretšwe le go netefatša go kgetholla kganyetšano mehuta ya dikokonyana tša Afrika Borwa tša go ja korong tše ditšwang Russia le go kgetholla dimela tsa poelo ya godimo. Ka gorialo, dimela tše mashome a seswai di ile tša netefatšwa go bona gore di tla kganyetša mehuta e nne ya dikokonyane, tšona e lego RWASA1, RWASA2, RWASA3 and RWASA4. Maswao a bonolo le a godišitšweng a ile a šomišwa go dimela tše mashometharo le motšo o tee tšeo di šetšego di kganyeditše RWASA3 le RWASA4 go kgetholla dimela tše di ka bontšhago lehlabula goba puno ya godimo. Dimela tše mashomepedi le metso e mehlano di bontšhitše go ganana le dikokonyane tše tše nne kamoka. Enyakile ka moka ga mashometharo ya dimela tse di kgethilwego di kgokagana le e tee ge e se tše nne tša ditšhupetšo tša diphatša tša lehutšo. Dimela tše di bohlokwa le mohola go ka šumišwa kgetholla tše kganyetšang RWASA5 ka moso le go hlahloba katišo ya diphatša tša lehutšo ka moso.Koring is een van die belangrikste graangewasse wêreldwyd en word in Suid-Afrika in drie verskillende produksiestreke verbou. Hierdie kommoditeit word egter beperk deur plae soos Russiese koringluis (RKL), asook deur ander biotiese, abiotiese en sosioekonomiese faktore. In hierdie studie is 80 koringgenotipes vir weerstand teen die vier Suid-Afrikaanse RKL biotipes, oftewel RWASA1, RWASA2, RWASA3 en RWASA4, geëvalueer. Hiervan was slegs 25 genotipes bestand teen al vier biotipes. Hierdie genotipes is derhalwe waardevolle toekomstige bronne vir die identifisering van weerstand teen die nuutste biotipe, RWASA5. Eenvoudige volgorde herhaling (SSR) en gekloofde versterkte polimorfisme volgorde (CAPS) merkers gekoppel aan hoër duisendkorrelmassa en korrelgetalle asook langer korrellengte-gene is op 31 RWASA3- en RWASA4-weerstandige genotipes getoets om nuwe bronne met 'n hoër opbrengspotensiaal te identifiseer. Byna al 31 genotipes wat in hierdie studie vir RKL weerstand gekies is, besit ten-minste een of meer opbrengspotensiaal-gene. Hierdie geselekteerde lyne is waardevolle bronne vir die analise van haplotipes in molekulêre genetika.College of Agriculture and Environmental SciencesM. Sc. (Agriculture

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

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)