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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Understanding the effect of genetic factors controlling flowering time is crucial to fine-tune crop adaptation to each target environment and maximize yield.
A set of spring durum wheat inbred lines carrying all but one of the possible allelic combinations at Ppd-A1 and Ppd-B1 genes was developed through a collaboration between IRTA and CIMMYT. The collection was grown during several years at four sites at latitudes ranging from 19?N to 41?N in order to assess the effect of Ppd-1 genes on development, biomass production and allocation, as well as grain yield formation.
Environmental constraints were responsible for most of the observed variation for flowering time and yield components. Latitude was a main driver of flowering time, which was later in northern sites and associated with lower minimum temperatures before flowering. Data on environmental constraints explaining a large proportion of grains m-2 and kernel weight variation will be presented. The effect on flowering time of Ppd-A1 alleles conferring photoperiod insensitivity was enhanced at sites with average daylength before flowering lower than 12h. Ppd-A1 caused a stronger effect on flowering time than Ppd-B1, which was found responsible for differences in grains m-2, associated with longer photoperiods from double-ridge to terminal spikelet stages. These differences in grains m-2, however, did not result in higher yields due to kernel weight compensation. Late flowering genotypes carrying alleles conferring photoperiod sensitivity had greater biomass at anthesis but it did not confer superior yields. Early flowering times were associated with higher yields in autumn-sowing sites due to a large contribution to yield of current photosynthesis during grain filling. Early flowering genotypes tended to yield more due to higher kernel weights, and the interaction of allele combination x environment will be discussed in the context of using allelic information as environment-specific guideline in breeding efforts.
Durum wheat production is globally important, but grain yield has been stagnating in recent decades. In order to ensure that its production maintains the pace with increasing demand, breeding for high grain yield must be supported by molecular-based methods. Genomic estimated breeding values for selection and genome scan were assessed as molecular tools holding maximum potential for durum wheat breeding. Four recombinant inbred line populations bred by inter-mating elite were sown in yield trials at five sites. All progenies were characterized using "genotyping by sequencing" method. A consensus map was developed, and missing genotypes were imputed using a Hidden Markov model to reach a total of 1987 polymorphic markers. Models accounting for genotype environment interactions were used to estimate the genetic component of each measured trait. Hence, Bayesian ridge regression was used to determine the predicted values and their relative accuracy in several combinations, testing full-sibs and half-sibs as training population for grain yield and 1,000 kernel weight. The high level of accuracy achieved suggests that GEBV for selection holds great potential for durum wheat breeding, as long as full-sibs are used as training populations, in combination with statistical models that account for G?E. In order to test the exploitability of genome scan to guide breeding crosses, a separate genome-wide association study was conducted. 288 elite were sown in the south of Morocco and at two sites along the Senegal River for two years. These sites show a temperature differential of 10?C. Implementing a GE model facilitated identifying the most heat tolerant among the tested entries. 8,173 polymorphic SNPs were inquired, and several associations could be identified between markers and the ability to withstand the heat gradient. Hence, GWAS holds great potential to increase genetic gain in breeding via increased accuracy in determining the crosses to be made.
Durum wheat (Triticum durum Desf.) is a major stable crop and it represents a base of the Mediterranean diet. This region is subject to a Mediterranean climate, which is extremely unpredictable with severe changes in moisture and temperature occurring each crop season. This unpredictability is summarized by breeders as GxE and the identification of traits controlling this interaction is quintessential to ensure stability in production season after season. To study the genetics of yield stability, four RILs populations derived from elite x elite crosses were assessed for yield and 1,000-kernel weights across five diverging environments in Morocco and Lebanon. These 550 RILs were characterized with 4,909 polymorphic SNPs via genotyping by sequencing. A consensus map was derived by merging the individual genetic maps of each population. Finally, imputation was used to fill all the missing haplotypes and reach a reduction of missing data to below 8%. Several significant QTLs were identified to be linked to TKW, grain yield and a stability index, namely AMMI wide adaptation index (AWAI). A second approach to identify loci controlling stability was the use of a global panel of 288 elites, accessions and landraces tested in 15 diverging environment. Multi-locations data were compiled via GxE models to derive the AWAI stability index. In addition, this panel was characterized with 8,173 polymorphic SNPs via Axiom 35K array. Significant associations were identified for all traits, including QTLs unique to AWAI. The sum of the identified QTLs can now be pyramid via marker assisted selection and molecular designed crosses in order to obtain very stable cultivars.
Leaf rust is an important worldwide disease on wheat caused by the fungus Puccinia triticina. Great infections on durum wheat occurred in Southern Spain in the 2000s but diminished in recent years due to deployment of resistant varieties and application of fungicides by farmers. A leaf rust survey was carried out from the 2009-15 period to monitor the virulence spectrum of the prevailing pathotypes. A total of 84 leaf rust isolates were collected on durum wheat fields. From those, single culture were obtained and used to inoculate a set of 27 differential isolines of the susceptible variety Thatcher. In addition 8 durum varieties with known Lr genes were also included.
The main highlight is that the resistance conferred by the popular Lr14a gene was broke up in 2013, but since then virulence to this gene is not widespread. In total, 23% of the isolates were virulent to the lines containing Lr14a. Lr1, Lr3, Lr3bg, Lr16, Lr24, Lr26, and Lr28 are very effective. Lines carrying Lr2c, Lr10, Lr14b, Lr20, Lr23, and LrB displayed susceptibility to most isolates. The durum varieties Jupare (Lr27+Lr31), Guayacan (Lr61), Storlom (Lr3+) and Camayo (LrCam) are also resistant against all isolates tested. Diversification of Lr genes is needed in the coming varieties to delay the appearance of new virulent races.
Wheat is a major food crop in West Africa, but its production is significantly affected by severe heat. Unfortunately, these types of high temperatures are also becoming frequent in other regions where wheat is commonly grown. In an attempt to improve durum wheat tolerance to heat, a collection of 287 elite breeding lines, including several from both ICARDA and CIMMYT, was assessed for response to heat stress in two irrigated sites along the Senegal River: Fanaye, Senegal and Kaedi, Mauritania during 2014-2015, and 2015-2016 winter seasons. The maximum recorded grain yield was 5t ha-1, which was achieved after just 90 days from sowing to harvesting. Phenological traits (heading, maturity and grain filling period) and yield components (1000-kernel weight, spike density and biomass) had also large phenotypic variation and a significant effect on grain yield performance. This panel was genotyped by 35K Axiom to generate 8,173 polymorphic SNPs. Genomic scans identified a total of 34 significant association between single nucleotide polymorphisms (SNPs) and traits across the four environments, including 15 related to phenological adaptation, 12 controlling grain yield components, and seven linked to grain yield per se. The identification of these genomic regions can now be used to design targeted crosses to pyramid heat tolerance quantitative trait loci (QTL), while the SNPs underlying these QTL can be deployed to accelerate selection process facilitated by DNA-aided breeding.
Our research objective is to identify new resistance genes in durum wheat that are effective against TTKSK and other significant stem rust pathogen races that could be utilized in durum breeding. We characterized 8,000 accessions for stem rust response in the field (Debre Zeit, Ethiopia, and St. Paul, MN). Accessions with resistant to moderately resistant responses in multiple field evaluations were evaluated at the seedling stage for resistance to races TTKSK, TRTTF, TTTTF, JRCQC, TKTTF, and six representative U.S. races. We identified 438 durum accessions resistant to moderately resistant in all field evaluations. Among the field-resistant accessions, 273 were resistant to all races used in seedling evaluations. Accessions susceptible at the seedling stage are being evaluated for the presence of adult plant resistance genes. The highest frequencies of resistant lines include landraces from East and North Africa (Ethiopia and Egypt) and advanced breeding lines and cultivars from North America (Mexico and USA). DNA markers will be performed to identify the presence of durum stem rust resistance genes, including Sr13, Sr8155B1, Sr11, and Sr8a. Nineteen resistant accessions were selected to investigate the genetics of TTKSK and TRTTF resistance. Results from evaluating F2 and F2:3 generations from biparental crosses revealed that resistance to race TTKSK was conferred mostly by one or two genes with dominant and recessive actions. Additional resistance genes were identified when populations were evaluated against race TRTTF. A bulk segregant analysis approach is being used to map the resistance in selected lines using the 90K SNP platform.
The recent emergence of new widely virulent and aggressive strains of rusts (particularly stripe and stem rust) is threatening Italian durum wheat (Triticum turgidum L. var. durum) production, especially under the trend of higher temperature and humidity. A big effort has been undertaken to explore the genetic variability for resistance to these fungal pathogens and discovering novel resistance genes. In particular, a wide set of tetraploid wheat lines was genotyped with several thousands of SNP markers and used for association mapping. This large collection consisted of a group of durum wheat cultivars, produced from the beginning of the last century up to now, a collection of wild emmer wheats (T. dicoccoides), and lines belonging to other wild and domesticated tetraploid subspecies, as a large untapped source of genetic diversity. In a tight cooperation with the University of Minnesota, this collection was evaluated for reaction to several races of stem and stripe rust pathogens in both controlled greenhouse and field conditions. Among the genotypes belonging to the collection are parents of segregating populations which were used for the validation of mapping results. Novel resistance loci were identified, that can be incorporated into new durum varieties through breeding programs. The QTLs found in this study, together with those available in literature, were projected to the recently sequenced durum wheat genome in order to define more precisely the chromosome regions and candidate genes involved in resistance to rusts. Lines which were resistant to multiple races of rust pathogens were also found among both T. dicoccoides and durum wheat cultivars as a source of resistance genes, whose cloning will be undertaken based on the results here obtained.
This study was supported by the Italian Ministry of Foreign Affairs and International Cooperation, with the special grant RES-WHEAT.
Eleven durum wheat (Triticum durum Desf.) genotypes were screened to select for drought-tolerance under in vitro immature embryos culture. Drought stress is induced by using five PEG concentrations (0, 200, 270, 295 and 310 g/l of PEG 6000). Results showed, for all studied traits, significant differences among PEG treatments and genotypes. In fact, increasing PEG concentration decreases relative growth rate, callus water content, relative water content, in vitro tolerance and relative tolerance. Biplot analysis indicated that the first two PCs (principal components 1 and 2) explain 70.5 % and showed that Karim, Mahmoudi and Om Rabiaa are respectively the most drought tolerant varieties tested, however, Ben Bechir, Maghrbi and Nasr were the most sensitive.
Wild species with valuable genetic heritage was used long time ago in interspecific crosses to improve cultivated plants adaptation to environmental constraints. The objective of this study is to transfer the salinity tolerance of Hordeum marinum, a wild barley species, to three durum wheat varieties (Karim, Razzek and Nasr) by intergeneric crosses. In order to skip the incompatibility between these species, in vitro immature embryo rescue was performed using B5 medium (Gamborg et al., 1968). The results showed that the genotype has an important effect on the success of the crosses and the rate of regenerated plants. We have found that 34.21% of the embryos derived from hybridization Razzek x Hordeum marinum has regenerated haploid plantlets, 5.88% for Karim x Hordeum marinum cross, and 2.78% for Nasr x Hordeum marinum.
The obtained chromosomal stock of the hybrid haploid plants was doubled by colchicine treatment concentrated at 0.05%. The rate of doubled haploid plants were reduced after colchicine treatment to 26.32% for Razzek x Hordeum marinum cross, 0% for Karim crossed with Hordeum marinum and remained unchanged for Nasr x Hordeum marinum.
The doubled haploids obtained are subjected to salt stress (6-12 g/l) in order to evaluate their tolerance to salinity.