Resistance of synthetic hexaploid wheat to the leaf rust pathogen

Background. One of the promising sources for enrichment of the common wheat (Triticum aestivum L.) gene pool with new alleles is synthetic hexaploid wheat (SHW), or allopolyploids from crossing tetraploid wheats (2n = 4x = 28, BBAA) with accessions of Aegilops tauschii Coss. (2n = 2x = 14, DD), and subsequent doubling of the chromosome number in the hybrids. Objectives of the study were to evaluate the SHW accessions from the VIR collection for resistance to Puccinia triticina Erikss. populations collected in Russia; genotype the accessions; and summarize information from the published sources concerning the resistance of the studied accessions to other harmful diseases and pests.Materials and methods. Resistance of 36 SHW accessions from the VIR collection to the populations of P. triticina was assessed in the laboratory and in the field, under artificial infection pressure, using the techniques developed by the Institute of Plant Protection. A phytopathological test and PCR markers were used to identify the Lr genes.Results and conclusion. The SHW accessions were characterized according to their resistance to the Russian populations of the wheat leaf rust pathogen. The sources of resistance in the phase of emergence and in adult plants were identified. The phytopathological test isolated three accessions with Lr23; the PCR marker of Lr21=Lr40 was found in 11 accessions, Lr39=Lr41 in 19, and Lr22a in 3. At the same time, k-65496, k-65515 and k-65517 had si multaneously Lr21=Lr40 and Lr39=Lr41, while k-65497, k-65503 and k-65508 had Lr22a and Lr39=Lr41. The analysis of published data showed that many of the studied SHW accessions were also resistant to other harmful diseases and insect pests, so they are of interest for further studying and possible use in domestic breeding.

Characterization of the Durum Wheat-Aegilops tauschii 4D(4B) Disomic Substitution Line YL-443 With Superior Characteristics of High Yielding and Stripe Rust Resistance

Durum wheat is one of the important food and cash crops. The main goals in current breeding programs are improving its low yield potential, kernel characteristics, and lack of resistance or tolerance to some biotic and abiotic stresses. In this study, a nascent synthesized hexaploid wheat Lanmai/AT23 is used as the female parent in crosses with its AB genome donor Lanmai. A tetraploid line YL-443 with supernumerary spikelets and high resistance to stripe rust was selected out from the pentaploid F7 progeny. Somatic analysis using multicolor fluorescence in situ hybridization (mc-FISH) revealed that this line is a disomic substitution line with the 4B chromosome pair of Lanmai replaced by the 4D chromosome pair of Aegilops tauschii AT23. Comparing with Lanmai, YL-443 shows an increase in the number of spikelets and florets per spike by 36.3 and 75.9%, respectively. The stripe rust resistance gene Yr28 carried on the 4D chromosome was fully expressed in the tetraploid background. The present 4D(4B) disomic substitution line YL-443 was distinguished from the previously reported 4D(4B) lines with the 4D chromosomes from Chinese Spring (CS). Our study demonstrated that YL-443 can be used as elite germplasm for durum wheat breeding targeting high yield potential and stripe rust resistance. The Yr28-specific PCR marker and the 4D chromosome-specific KASP markers together with its unique features of pubescent leaf sheath and auricles can be utilized for assisting selection in breeding.

Marker Development for Differentiation of Fusarium oxysporum f. sp. Niveum Race 3 from Races 1 and 2

Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum (FON), is pathogenic only to watermelon and has become one of the main limiting factors in watermelon production internationally. Detection methods for this pathogen are limited, with few published molecular assays available to differentiate FON from other formae speciales of F. oxysporum. FON has four known races that vary in virulence but are difficult and costly to differentiate using traditional inoculation methods and only race 2 can be differentiated molecularly. In this study, genomic and chromosomal comparisons facilitated the development of a conventional polymerase chain reaction (PCR) assay that could differentiate race 3 from races 1 and 2, and by using two other published PCR markers in unison with the new marker, the three races could be differentiated. The new PCR marker, FNR3-F/FNR3-R, amplified a 511 bp region on the “pathogenicity chromosome” of the FON genome that is absent in race 3. FNR3-F/FNR3-R detected genomic DNA down to 2.0 pg/µL. This marker, along with two previously published FON markers, was successfully applied to test over 160 pathogenic FON isolates from Florida, Georgia, and South Carolina. Together, these three FON primer sets worked well for differentiating races 1, 2, and 3 of FON. For each marker, a greater proportion (60 to 90%) of molecular results agreed with the traditional bioassay method of race differentiation compared to those that did not. The new PCR marker should be useful to differentiate FON races and improve Fusarium wilt research.

Identification of leaf rust resistance genes Lr34 and Lr46 in common wheat (Triticum aestivum L. ssp. aestivum) lines of different origin using multiplex PCR

Leaf rust caused by the fungus Puccinia recondita f. sp. tritici is one of the most dangerous diseases of common wheat. Infections caused by fungal pathogens reduce the quantity and quality of yields of many cereal species. The most effective method to limit plant infection is to use cultivars that show rust resistance. Genetically conditioned horizontal-type resistance (racial-nonspecific) is a desirable trait because it is characterized by more stable expression compared to major (R) genes that induce racially specific resistance, often overcome by pathogens. Horizontal resistance is conditioned by the presence of slow rust genes, which include genes Lr34 and Lr46. This study aimed to identify markers linked to both genes in 64 common wheat lines and to develop multiplex PCR reaction conditions that were applied to identify both genes simultaneously. The degree of infestation of the analyzed lines was also assessed in field conditions during the growing season of 2017 and 2018. Simple sequence repeat anchored-polymerase chain reaction (SSR-PCR) marker csLV was identified during analysis in line PHR 4947. The presence of a specific sequence has also been confirmed in multiplex PCR analyses. In addition to gene Lr34, gene Lr46 was identified in this genotype. Lines PHR 4947 and PHR 4819 were characterized by the highest leaf rust resistance in field conditions. During STS-PCR analyses, the marker wmc44 of gene Lr46 was identified in most of the analyzed lines. This marker was not present in the following genotypes: PHR 4670, PHR 4800, PHR 4859, PHR 4907, PHR 4922, PHR 4949, PHR 4957, PHR 4995, and PHR 4997. The presence of a specific sequence has also been confirmed in multiplex PCR analyses. Genotypes carrying the markers of the analyzed gene showed good resistance to leaf rust in field conditions in both 2017 and 2018. Research has demonstrated that marker assisted selection (MAS) and multiplex PCR techniques are excellent tools for selecting genotypes resistant to leaf rust.

Genetic and comparative mapping of Lupinus luteus L. highlight syntenic regions with major orthologous genes controlling anthracnose resistance and flowering time

Anthracnose susceptibility and ill-adapted flowering time severely affect Lupinus luteus yield, which has high seed protein content, is excellent for sustainable agriculture, but requires genetic improvement to fulfil its potential. This study aimed to (1) develop a genetic map; (2) define collinearity and regions of synteny with Lupinus angustifolius; and (3) map QTLs/candidate genes for anthracnose resistant and flowering time. A few linkage groups/genomic regions tended to be associated with segregation distortion, but did not affect the map. The developed map showed collinearity, and syntenic regions with L. angustifolius. Major QTLs were mapped in syntenic regions. Alleles from the wild parent and cultivar, explained 75% of the phenotypic variance for anthracnose resistance and 83% for early flowering, respectively. Marker sequences flanking the QTLs showed high homology with the Lanr1 gene and Flowering-locus-T of L. angustifolius. This suggests orthologous genes for both traits in the L. luteus genome. The findings are remarkable, revealing the potential to combine early flowering/anthracnose resistant in fulfilling yield capacity in L. luteus, and can be a major strategy in the genetic improvement and usage of this species for sustainable protein production. Allele sequences and PCR-marker tagging of these genes are being applied in marker assisted selection.

Identification of an Elite Wheat-Rye T1RS·1BL Translocation Line Conferring High Resistance to Powdery Mildew and Stripe Rust

Wheat-rye T1RS·1BL translocations have been widely used worldwide in wheat production for multiple disease resistance and superior yield traits. However, many T1RS·1BL translocations have successively lost their resistance to pathogens due to the coevolution of pathogen virulence with host resistance. Because of the extensive variation in rye (Secale cereale L.) as a naturally cross-pollinating relative of wheat, it still has promise to widen the variation of 1RS and to fully realize its application value in wheat improvement. In the present study, the wheat-rye breeding line R2207 was characterized by comprehensive analyses using genomic in situ hybridization (GISH), multicolor fluorescence in situ hybridization with multiple probes, multicolor GISH, and molecular marker analysis, and then was proven to be a cytogenetically stable wheat-rye T1RS·1BL translocation line. Based on the disease responses to different isolates of powdery mildew and genetic analysis, R2207 appears to possess a novel variation for resistance, which was confirmed to be located on the rye chromosome arm 1RS. Line R2207 also exhibited high levels of resistance to stripe rust at both seedling and adult stages, as well as enhanced agronomic performance, so it has been transferred into a large number of commercial cultivars using an efficient 1RS-specific kompetitive allele specific PCR marker for marker-assisted selection.