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Malika', a hard red spring wheat (Triticum aestivum L.) cultivar developed using doubled haploid technology by the Institut National de la Recherche Agronomique (INRA), Morocco, and tested as 06DHBW48, was approved for release in 2016 by the Office National de S?curit? Sanitaire des Produits Alimentaires (ONSSA), Morocco. Malika was selected from the doubled haploids derived from the cross 'Achtar3*//'Kanz'/Ks85-8-4). Achtar and Kanz are Moroccan varieties originating from segregating populations from CIMMYT. Achtar and Kanz are a well adapted to Moroccan conditions but susceptible to the Hessian fly, yellow rusts and some races of leaf rust. 'Achtar' was crossed with it in order to incorporate the Hessian fly resistance, yellow rust resistance and leaf rust resistance and 'Achtar' was crossed with Kanz/Ks85-8-4 having resistance to Hessian fly, yellow rust and leaf rust. Backcrossed 3 times with 'Achtar', and selected lines having resistance to the Hessian fly, yellow rust and leaf rust from the population derived from each backcross. Finally the selected the resistant line was used develop doubled haploids. The doubled haploid lines produced were tested in the laboratory and field for Hessian fly and the rust resistance. The resistant lines were incorporated in the multi-local yield trials and three promising lines with the resistance to Hessian fly, yellow rust and leaf rust and better yield and quality were submitted for registration in the official catalog in 2014. After 2 years of testing (years 2014-15 and 2015-16), one line (06DHBW48) was accepted for the registration and designated as 'Malika'. 'Malika' is a semi-dwarf variety, well adapted to semi-arid regions, early maturing, high yielding, tolerant to drought and resistant to Hessian fly, leaf rust and yellow rust.
Leaf rust disease, caused by the fungal pathogen Puccinia triticina, is a major biotic constraint of wheat production worldwide. Genetic resistance is the most effective, economic, and environmentally safe method to control and reduce losses caused by this disease. More than 70 leaf rust resistance genes have been identified and mapped to specific chromosomes; however, continuous evolution of new leaf rust races requires constant search for new sources of resistance with novel QTL/genes. The objectives of this study were to identify sources of resistance, and to map genomic loci associated with leaf rust resistance using genome wide association study (GWAS) approach. Phenotypic evaluation of 297 spring wheat genotypes against a prevalent race of leaf rust in Georgia revealed that most of the genotypes were susceptible, and only 24 genotypes were found resistant. Furthermore, GWAS detected 10 markers on chromosomes 2A, 2B, 6A, 7A, and 7B significantly associated with leaf rust resistance. A marker on chromosome 7AS was identified revealing a novel genomic region associated with leaf rust resistance. The new identified sources of resistance and QTL could be used in wheat breeding programs to improve leaf rust resistance.
Intensive breeding and replacement of traditional landraces by modern cultivars led to the narrowing of genetic variation in cultivated wheat. The most sustainable method for wheat improvement is utilization of genetic diversity from wheat wild relatives such as Aegilops speltoides that has a diversity of genes for resistance to leaf rust (LR). A high pairing-inducing Ae. speltoides strain collected from Israel was introgressed into T. turgidum subsp. durum var. landrace Nursi. The F1 plants were treated with colchicine to induce chromosome doubling. The resulting hexaploid plants were crossed to bread wheat cv. Beit-Lehem and F3 plants were backcrossed three times to bread wheat cv. Barnir. Each generation was selected for LR resistance to P. triticina isolate #1010 and five resistant wheat-Ae. speltoides introgression lines (ILs) designated DK1 to DK5 were selected. These Ae. speltoides ILs were genotyped using the 90K Infinium SNP assay and most of the polymorphic markers were mapped to chromosome 1B suggesting that the Ae. speltoides introgressions encompass most of this chromosome. To test if the newly identified gene is identical to Lr51, that was also introgressed from Ae. speltoides to chromosome 1B of bread wheat, the DK ILs were genotyped with the molecular marker AGA7 that was shown to be linked to Lr51. The Ae. speltoides AGA7 allele was absent in the DK ILs suggesting that these genotypes are not carrying the Lr51 introgression. Moreover, we performed an allelism test. Spring wheat cv. Kern harboring resistance gene Lr51 was crossed with DK2 and an F2 segregation ratio of 15R:1S was obtained, indicating that the resistance was conditioned by two independent dominant genes. Overall, our results suggest that DK2 carries a new leaf rust resistance gene from Ae. speltoides and this gene has potential for wheat improvement.
Leaf rust (LR), caused by Puccinia triticina, is among the most important diseases of wheat (Triticum aestivum L.) crops globally. The most sustainable method for controlling rust pathogens is deployment of cultivars incorporating durable forms of resistance, such as adult plant resistance (APR). However, phenotyping breeding populations or germplasm collections for LR resistance in the field is dependent on weather conditions and limited to only once a year. In this study, we report a protocol for phenotyping APR to LR incorporating ‘speed breeding’ technology, which utilizes controlled temperature regimes and 24-hour light to provide accelerated growth conditions (AGC) – enabling up to 6 plant generations of wheat per year. A panel of 22 genotypes, including disease standards carrying known APR genes along with a diversity panel comprising 300 accessions (including winter types and landraces) were characterized for resistance to LR under AGC and in the field. Analysis of genotypes displaying APR revealed that disease response expressed on flag–2 leaves under AGC was highly correlated with field-based measures (R2 = 0.76). Analysis of the diversity panel indicated that APR was expressed by plants that had obtained the stem elongation stage (i.e. GS≥30) prior to inoculation. Despite the high degree of genetic diversity in the panel, strong correlations between LR response under AGC and the field were observed, and were further improved when field response was adjusted based on growth stage (R2 = 0.81). The diversity panel was also screened with DNA markers for known APR genes (Lr34, Lr46 and Lr67), which identified 22 accessions carrying potentially novel sources. This method integrates assessment at both seedling and adult growth stages and requires only seven weeks to complete, enabling up to seven consecutive assays annually. When coupled with ‘speed breeding’, this approach could also accelerate introgression of resistance genes into adapted wheat cultivars.
A wheat genotype PBW343+Gpc-B1+LR24 containing the high grain protein content (GPC) gene Gpc-B1 linked to marker Xucw108 was used as the donor parent to transfer Gpc-B1 and Lr24 into Eastern Gangetic Plains (EGP) cv. HUW234 and HUW468 that were released in 1986 and 1999, respectively. The backcrossing program involved the following steps: (i) foreground selection, (ii) marker selection, and (iii) recovery of recipient parent genome. Grain protein contents were recorded for all selected plants from the BC2F2:3 generation. The dominant marker Xucw108 was used for foreground selection, and heterozygous plants were identified through progeny testing. For RPG recovery, both genotypic and phenotypic selection was used. Introgression of the high GPC gene into the recipient background without yield loss was completed in 5 years, starting from 2009-10 (F1) and completed in 2013-14 (BC2F5). A conventional selection program would take the same time to reach BC2F5 but ensuring the transfer of GPC would not not be possible. Ten selected single plants from the BC2F3:4 generation had comparable yields of the parents with 26% higher GPC than the recurrent parent HUW 234. Eight selected plants had comparable yields and 34% higher GPC than HUW 468. Multi-row progenies (BC2F4 and BC2F5) of each selected plant were evaluated in yield traits with the donor and recipient parents as controls during 2012-13 and 2013-14. Two lines based on each recurrent parent were identified with significantly higher GPC with no yield penalty. The study reinforced the belief that MAS in combination with phenotypic selection could be a useful strategy to develop high GPC genotypes without sacrificing grain yield. These lines will be submitted to national trial where MAS derived lines require only two years of testing compared to four years for conventionally bred lines.
Leaf rust is endemic to all wheat-growing regions of the world. Resistance to leaf rust in wheat cultivars is controlled either by all stage resistance (ASR) or by adult plant resistance (APR) genes. Although deployment of single ASR genes can provide high levels of resistance, these are usually overcome by virulence in pathogen populations. In contrast, individual APR genes often provide low levels of resistance and combinations of three to four genes are necessary to achieve adequate resistance for crop protection. This kind of APR has proven to be durable. APR gene Lr48 in a single plant selection of Condor (CSP44) was mapped on chromosome 2BS and was flanked by markers gwm429b (6.1 cM, distal) and barc7 (7.3 cM, proximal) (Bansal et al. 2008, Theor. Appl. Genet. 117:307-312). The present study was planned to identify markers more closely linked to Lr48. Selective genotyping by 90K Infinium Assay identified 27 SNP markers linked with Lr48. The SNP sequences were used to design Kompetitive Allele-Specific Primers (KASP). Eleven KASP markers showing clear clustering were genotyped on a RIL population using the CFX96 Touch™ real-time PCR detection system (Biorad, USA). KASP marker IWB72894 co-segregated with Lr48.
Leaf rust (caused by Puccinia triticina) continues to be the most important and widespread foliar disease of wheat in the Southern Cone. The P. triticina population of the region is extremely dynamic, leading to short-lived resistance in commercial cultivars. Some high yielding materials susceptible to leaf rust have been released and their increasing cultivation relies on fungicide applications to control leaf rust. The most important challenge of breeding programs in the Southern Cone is to incorporate durable leaf rust resistance in high yielding cultivars. These cultivars must also combine resistance to other relevant diseases and meet industrial quality standards demanded by the market. Leaf rust resistance in wheat varieties and lines lies mostly in combinations of seedling resistance genes or combinations of these with adult plant resistance (APR), including Lr34. Few recently released cultivars carry APR to leaf rust that might be expected to be durable. Since efforts to introduce slow rusting into high yielding adapted germplasm are increasing in most countries, more cultivars carrying this type of resistance will likely be released. If major genes are used, the introduction of effective genes not present in the regional germplasm will increase the diversity of resistance. Molecular markers are used in breeding in Argentina and are starting to be implemented in Brazil and Uruguay. Increased use of molecular tools could improve genetic progress in breeding programs, allow identification of APR genes present in current regional germplasm, and facilitate identification of new resistance genes.
Leaf rust represents the major threat to wheat production in Russia and Ukraine. It has been present for many years and epidemics occur in different regions on both winter and spring wheat. In some regions there is evidence of more frequent epidemics, probably due to higher precipitation as a result of climate change. There is evidence that the virulence of the leaf rust population in Ukraine and European Russia and on winter wheat and spring wheat is similar. The pathogen population structure in Western Siberia is also similar to the European part, although there are some significant differences based on the genes employed in different regions. Ukrainian wheat breeders mostly rely on major resistance genes from wide crosses and have succeeded in developing resistant varieties. The North Caucasus winter wheat breeding programs apply the strategy of deploying varieties with different types of resistance and genes. This approach resulted in decreased leaf rust incidence in the region. Genes Lr23 and Lr19 deployed in spring wheat in the Volga region were rapidly overcome by the pathogen. There are continuing efforts to incorporate resistance from wild species. The first leaf rust resistant spring wheat varieties released in Western Siberia possessed gene LrTR which protected the crop for 10-15 years, but was eventually broken in 2007. Slow rusting is being utilized in several breeding programs in Russia and Ukraine, but has not become a major strategy.