Quantitative trait loci mapping of adult‐plant resistance to leaf rust in a Fundulea 900 × ‘Thatcher’ wheat cross

Wheat leaf rust (LR), caused by the obligate biotrophic fungus Puccinia triticina (Pt), is a destructive foliar disease of common wheat (Triticum aestivum L.) worldwide. The most effective, economic means to control the disease is resistant cultivars. The Romanian wheat line Fundulea 900 showed high resistance to LR in the field. To identify the basis of resistance to LR in Fundulea 900, a population of 188 F_2:3 lines from the cross Fundulea 900/‘Thatcher’ was phenotyped for LR severity during the 2010–2011, 2011–2012 and 2012–2013 cropping seasons in the field at Baoding, Hebei Province. Bulked segregant analysis and simple sequence repeat markers were used to identify the quantitative trait loci (QTLs) for LR adult‐plant resistance in the population. Three QTLs were detected and designated as QLr.hebau‐1BL, QLr.hebau‐2DS and QLr.hebau‐7DS. Based on the chromosome positions and molecular marker tests, QLr.hebau‐1BL is Lr46, and QLr.hebau‐7DS is Lr34. QLr.hebau‐2DS was derived from ‘Thatcher’ and was close to Lr22. This result suggests that Lr22b may confer residual resistance on field nurseries when challenged with isolates virulent on Lr22b, or another gene linked to Lr22b confers this resistance from ‘Thatcher’. This study confirms the value of Lr34 and Lr46 in breeding for LR resistance in China; the contribution of the QTL to chromosome 2D needs further validation.     

Introducing host‐plant resistance to anthracnose in Kyrgyz common bean through inoculation‐based and marker‐aided selection

Common bean (Phaseolus vulgaris L.) is one of the most important legume crops for human consumption. However, its grain yield can be reduced by up to 90% by the seedborne disease, anthracnose. Fungicide treatment is costly and time‐consuming. The introduction of host plant resistance against this disease appears, therefore, to be crucial for enhancing the productivity of this crop in Kyrgyzstan. The use of DNA‐based markers in backcrossing programmes may help speed up the breeding for resistance. In this study, we used a combination of inoculation tests and a DNA marker (SCAreoli marker) to track the transfer of host‐plant resistance (Co‐2 gene) from two donor cultivars, ‘Vaillant’ and ‘Flagrano’, to susceptible Kyrgyz cultivars ‘Ryabaya’, ‘Kytayanka’ and ‘Lopatka’, which are widely grown in the country. The segregating offspring were evaluated to test the reliability of the SCAreoli marker as selection aid for host‐plant resistance to anthracnose. Our study showed that a co‐dominant DNA marker can successfully be used in backcross breeding to distinguish segregating material in different market classes of common bean.     

Characterization of broad‐spectrum resistance to Soybean mosaic virus in soybean [Glycine max (L.) Merr.] cultivar ‘RN‐9’

Soybean mosaic virus (SMV) can cause serious yield losses in soybean. Soybean cultivar ‘RN‐9’ is resistant to 15 of 21 SMV strains. To well‐characterize this invaluable broad‐spectrum SMV‐resistance, populations (F₁, F₂ and F_2:3) derived from resistant (R) × susceptible (S) and R × R crosses were tested for SMV‐SC18 resistance. Genetic analysis revealed that SC18 resistance in ‘RN‐9’ plus two elite SMV‐resistant genotypes (‘Qihuang No.1’ and ‘Kefeng No.1’) are controlled by independently single dominant genes. Linkage analysis showed that the resistance of ‘RN‐9’ to SMV strains SC10, SC14, SC15 and SC18 is controlled by more than one gene(s). Moreover, Rsc10‐r and Rsc18‐r were both positioned between the two simple sequence repeats markers Satt286 and Satt277, while Rsc14‐r was fine‐mapped in 136.8‐kb genomic region containing sixteen genes, flanked by BARCSOYSSR_06_0786 and BARCSOYSSR_06_0790 at genetic distances of 3.79 and 4.14 cM, respectively. Allelic sequence comparison showed that Cytochrome P450‐encoding genes (Glyma.06g176000 and Glyma.06g176100) likely confer the resistance to SC14 in ‘RN‐9’. Our results would facilitate the breeding of broad‐spectrum and durable SMV resistance in soybeans.     

Characterization and allelism of soybean mosaic virus strain SC3 resistance in ‘Qihuang-1’ derived soybean cultivars

Soybean mosaic virus is a severe constraint of soybean production in China. A total of country-wide 22 SMV strains (SC1-SC22) were identified. Of these, SC3 is a major strain widely distributed in Huanghuai and Yangtze River Valley region of China. Soybean cultivar ‘Qihuang-1’ contains R_SC3Q locus conditioning the resistance to SC3 and is an important parental line extensively used to breed the soybean cultivars in China. The objective of this study was to elucidate the genetic pattern of SC3 resistance genes in cultivars developed from ‘Qihuang-1’ or its derivative lines. Hence, we have evaluated the SC3 resistance in 91 cultivars developed from ‘Qihuang-1’ or its derivative lines. The results showed that a total of 43 cultivars exhibited resistance to the SC3 strain. Among them, 37 cultivars were derived from ‘Qihuang-1’. Then, we have detected the R_SC3Q loci in these cultivars using four SSR markers (Satt334, Sct_033, BARCSOYSSR_13_1114 and BARCSOYSSR_13_1136). It revealed that, among the 37 resistant cultivars derived from ‘Qihuang-1’, there are 20 cultivars containing R_SC3Q loci. Moreover, the allelic relationship of resistance genes was analysed using the crosses from resistance × resistance between ‘Qihuang-1’ and its resistant derived cultivars. The results showed that the resistance genes of ‘Qihuang-1’ and its 20 cultivars were allelic. But it is not allelic with those of the other 17 cultivars, different from ‘Qihuang-1’, and also, R_SC3Q does not condition the resistance. These results will be beneficial to exploring the transmission of resistance genes of ‘Qihuang-1’ and will be useful to the disease resistance breeding of soybean.     

QTL mapping of adult‐plant resistance to stripe rust in a ‘Lumai 21 × Jingshuang 16’ wheat population

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is a devastating fungal disease in common wheat (Triticum aestivum L.) worldwide. Chinese wheat cultivars ‘Lumai 21’ and ‘Jingshuang 16’ show moderate levels of adult‐plant resistance (APR) to stripe rust in the field, and they showed a mean maximum disease severity (MDS) ranging from 24 to 56.7% and 26 to 59%, respectively, across different environments. The aim of this study was to identify quantitative trait loci (QTL) for resistance to stripe rust in an F₃ population of 199 lines derived from ‘Lumai 21’ × ‘Jingshuang 16’. The F₃ lines were evaluated for MDS in Qingshui, Gansu province, and Chengdu, Sichuan province, in the 2009–2010 and 2010–2011 cropping seasons. Five QTL for APR were detected on chromosomes 2B (2 QTL), 2DS, 4DL and 5DS based on mean MDS in each environment and averaged values from all three environments. These QTL were designated QYr.caas‐2BS.2, QYr.caas‐2BL.2, QYr.caas‐2DS.2, QYr.caas‐4DL.2 and QYr.caas‐5DS, respectively. QYr.caas‐2DS.2 and QYr.caas‐5DS were detected in all three environments, explaining 2.3–18.2% and 5.1–18.0% of the phenotypic variance, respectively. In addition, QYr.caas‐2BS.2 and QYr.caas‐2BL.2 colocated with QTL for powdery mildew resistance reported in a previous study. These APR genes and their linked molecular markers are potentially useful for improving stripe rust and powdery mildew resistances in wheat breeding.     

Molecular cytogenetic characterization and phenotypic evaluation of new wheat–rye lines derived from hexaploid triticale ‘Certa’ × common wheat hybrids

Hexaploid triticale contains valuable genes from both tetraploid wheat and rye and plays an important role in wheat breeding programmes. In order to explore the potential of hexaploid triticale ‘Certa’ in wheat improvement, two crosses were made using ‘Certa’ as female parent, and common wheat cultivars ‘Jinmai47’ (JM47) and ‘Xinong389’ (XN389) as male parents. The karyotyping of BCF_4:5 lines from Certa/JM47//JM47 and F_5:6 lines from Certa/XN389 was investigated using sequential fluorescence in situ hybridization (FISH). One 1B(1R) substitution line and five 1BL.1RS whole‐arm translocation lines were identified, one of which was found lacking ω‐secalin locus. Many structural alterations on wheat chromosomes were detected in the progeny. Great morphologic differences resulting from genetic variations were observed, among which the photosynthetic capability was increased while grain quality was slightly improved. Compared with both parents, the stripe rust resistance at adult stage was increased in lines derived from Certa/JM47//JM47, while it was decreased in lines derived from Certa/XN389. These newly developed lines might have the potential to be utilized in wheat improvement programmes.     

Genotype analysis of the wheat semidwarf Rht‐B1b and Rht‐D1b ancestral lineage

In wheat, semidwarfism resulting from reduced height (Rht)‐B1b and Rht‐D1b was integral to the ‘green revolution’. The principal donors of these alleles are ‘Norin 10’, ‘Seu Seun 27’ and ‘Suwon 92’ that, according to historical records, inherited semidwarfism from the Japanese landrace ‘Daruma’. The objective of this study was to examine the origins of Rht‐B1b and Rht‐D1b by growing multiple seed bank sources of cultivars comprising the historical pedigrees of the principal donor lines and scoring Rht‐1 genotype and plant height. This revealed that ‘Norin 10’ and ‘Suwon 92’ sources contained Rht‐B1b and Rht‐D1b, but the ‘Seu Seun 27’ source did not contain a semidwarf allele. Neither Rht‐B1b nor Rht‐D1b could be definitively traced back to ‘Daruma’, and both ‘Daruma’ sources contained only Rht‐B1b. However, ‘Daruma’ remains the most likely donor of Rht‐B1b and Rht‐D1b. We suggest that the disparity between historical pedigrees and Rht‐1 genotypes occurs because the genetic make‐up of seed bank sources differs from that of the cultivars actually used in the pedigrees. Some evidence also suggests that an alternative Rht‐D1b donor may exist.     

A novel aphid resistance locus in cowpea identified by combining SSR and SNP markers

The utility of combining simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) marker genotyping was determined for genetically mapping a novel aphid (Aphis craccivora) resistance locus in cowpea breeding line SARC 1‐57‐2 and for introgressing the resistance into elite cultivars by marker‐assisted backcrossing (MABC). The locus was tagged with codominant SSR marker CP 171F/172R with a recombination fraction of 5.91% in an F₂ population from ‘Apagbaala’ x SARC 1‐57‐2. A SNP‐genotyped biparental recombinant inbred line population was genotyped for CP 171F/172R, which was mapped to position 11.5 cM on linkage group (LG) 10 (physical position 30.514 Mb on chromosome Vu10). Using CP 171F/172R for foreground selection and a KASP‐SNP‐based marker panel for background selection in MABC, the resistance from SARC 1‐57‐2 was introduced into elite susceptible cultivar ‘Zaayura’. Five BC₄F₃ lines of improved ‘Zaayura’ that were isogenic except for the resistance locus region had phenotypes similar to SARC 1‐57‐2. This study identified a novel aphid resistance locus and demonstrated the effectiveness of integrating SSR and SNP markers for trait mapping and marker‐assisted breeding.     

Introgression of clubroot resistance into an elite pak choi inbred line through marker‐assisted introgression breeding

Clubroot is a soilborne disease that severely infects cruciferous species. Pak choi (Brassica rapa subsp. chinensis) is an economically important cruciferous crop cultivated throughout the world. However, no clubroot‐resistant germplasms have been identified in pak choi to date. To improve disease resistance, we used marker‐assisted selection (MAS) to introgress the clubroot resistance (CR) trait from the ‘CCR13685’ Chinese cabbage (B. rapa subsp. pekinensis) inbred line into an elite pak choi inbred line, ‘GHQ11021’. Genetic analysis of F₂ and BC₁ progeny showed that CR of ‘CCR13685’ was controlled by a single dominant gene. We designed nine candidate sequence‐characterized amplified region markers, K‐1 to K‐9, based on two molecular markers linked to the CR gene. We found that K‐3 co‐segregated with CR and an inoculation test confirmed that K‐3 could be used for MAS. Two introgression lines, BC₃‐1‐4 and BC₃‐2‐18, were developed using K‐3 for foreground selection. These lines displayed the same phenotypic properties as ‘GHQ11021’, but were highly resistant to clubroot, indicating that the CR gene of ‘CCR13685’ had been successfully introduced into pak choi.     

Genetics of resistance to bean golden mosaic virus in Phaseolus vulgaris L.

Summary The genetics of resistance to bean golden mosaic virus (BGMV) was studied in an 8×8 complete diallel cross of common bean, Phaseolus vulgaris L. The 28F₁ hybrids, their reciprocals, and eight parents were artificially inoculated with BGMV under glasshouse conditions. Data were recorded and analyzed for foliar yellowing, plant dwarfing, flower abortion, and pod formation, using a randomized complete block design with two replications.General combining ability (GCA) mean squares were highly significant (P<0.01) and larger than values for specific combining ability for all traits. Reciprocal and maternal effects were nonsignificant. Cultivars Royal Red and Alubia Cerrillos possessed significant negative and positive GCA for all traits, respectively. Porrillo Sintetico also had negative GCA for all traits except plant dwarfing. None of the GCA effects were significant for Great Northern 31 and PVA 1111. Positive associations existed among all traits studied.     

Deployment of cold tolerance loci from Oryza sativa ssp. Japonica cv. ‘Nipponbare’ in a high‐yielding Indica rice cultivar ‘93‐11’

Cold tolerance is a complex trait, and QTL pyramiding is required for rice breeding. In this study, a total of seven QTLs for cold tolerance in the Japonica rice variety ‘Nipponbare’ were identified in an F_2:3 population. A stably inherited major QTL, called qCTS11, was detected in the region adjacent to the centromere of chromosome 11. In a near‐isogenic line population, the QTL was further dissected into two linked loci, qCTS11.1 and qCTS11.2. Both of the homozygous alleles of qCTS11.1 and qCTS11.2 from ‘Nipponbare’ showed major positive effects on cold tolerance. Through pyramiding the linked QTLs in the cold‐sensitive Indica rice cultivar ‘93‐11’, we have developed a new elite, high‐yielding Indica variety with cold tolerance.     

Resistance to the Barley Yellow Mosaic Virus Complex — Differential Genotypic Reactions and Genetics of BaMMV-Resistance of Barley (Hordeum vulgare L.)

Barley yellow mosaic disease is caused by several viruses, i.e. barley yellow mosaic virus (BaYMV), barley mild mosaic virus (BaMMV) and BaYMV-2. The reaction of different barley germplasms to the barley mosaic viruses was studied in field and greenhouse experiments. The results show a complex situation; some varieties are resistant to all the viruses, while others are resistant to one or two of them only. Crosses between different barley germplasms were earned out in order to test whether genetic diversity of resistance against mosaic viruses does exist, particularly, BaMMV. A total of 45 foreign barley varieties were crossed to German cultivars carrying the resistance gene ym4. In F₂ of 27 crosses, no segregation could be detected, leading to the conclusion that the resistance genes of the foreign parents are allelic with ym4 e.g. Ym1 (‘Mokusekko 3’) and Ym2 (‘Mihori Hadaka 3’). A total of 18 crosses segregated in F₂ indicating that foreign parents, like ‘Chikurin Ibaraki 1’, ‘Iwate Omugi 1’, and “Anson Barley”, carry resistance genes different from the gene of German cultivars, e.g. ‘Asorbia’ or ‘Franka’. By means of statistical evaluation (Chi²-test), the observed segregation ratios were analyzed in order to obtain significant information on the heredity of resistance. All the resistance genes described here as being different from the gene ym4, act recessively. Most of the exotic varieties seem to carry only one resistance gene. In a few cases, more than one gene may be present.     

Variable resistance of bread wheat (Triticum aestivum) lines carrying 2NS/2AS translocation to wheat blast

Wheat blast disease, caused by Magnaporthe oryzae (anamorph Pyricularia oryzae), produces severe damage to wheat production in South America. It was observed that many resistant cultivars contain the 2NS/2AS translocation from Triticum ventricosum. In this study, we evaluate the presence of the 2NS/2AS translocation in 57 advanced breeding lines and one variety ‘Caninde 1’ from Paraguayan wheat germplasm, using VENTRIUP‐LN2 primers. The germplasm ‘Caninde 1 and 22’ of the breeding lines, found positive for the presence of 2NS/2AS translocation, were inoculated with a single aggressive Magnaporthe pathotype P14‐039, to assess their response to wheat blast infection under controlled conditions. Based on the disease infection score, ten of the breeding lines, ‘Caninde 1’ and ‘Milan’ (positive control), were classified as resistant. Three of the remaining breeding lines were classified as moderately resistant, five as moderately susceptible and other four as susceptible. Our results show that the expression of 2NS/2AS‐based blast resistance is more dependent on genetic background of the inserted germplasm than previously envisioned.     

Backcross breeding for improved resistance to common bacterial blight in pinto bean (Phaseolus vulgaris L.)

Common bacterial blight (CBB) caused by Xanthomonas campestris pv. phaseoli reduces common bean (Phaseolus vulgaris L.) yield and quality worldwide. Genetic resistance provides effective disease control; however. a high level of resistance is difficult to attain and does not exist in pinto bean, the most important dry bean market class in North America. Our objective was to determine if a backcross breeding approach with the aid of molecular markers linked to quantitative trait loci (QTL) for resistance to CBB in a donor parent could be used to attain higher levels of resistance to CBB in pinto bean. QTL conditioning CBB resistance from the donor parent XAN 159 were introgressed into the recurrent parent‘Chase’using classical backcross breeding and intermittent marker‐assisted selection.‘Chase’pinto bean is moderately resistant and the breeding line XAN 159 is highly resistant to Xanthomonas campestris. Marker assays confirmed the presence of independent QTL from GN no. 1 Sel 27 and XAN 159 in advanced backcross‐derived pinto bean lines with improved CBB resistance. Agronomic characteristics of‘Chase’were fully recovered in the backcross‐derived lines. An important QTL for CBB resistance from XAN 159 on linkage group B6 was not introgressed because tight linkage between this QTL and the dominant V allele that causes an unacceptable black‐mottled seed coat colour pattern in pinto bean could not be broken.     

Development of a kompetitive allele‐specific PCR marker for selection of the mutated Wx‐D1d allele in wheat breeding

Waxy (Wx) protein is a key enzyme for synthesis of amylose in endosperm. Amylose content in wheat grain influences the quality of end‐use products. Seven alleles have been described at the Wx‐D1 locus, but only two of them (Wx‐D1b, Wx‐D1e) were genotyped with codominant markers. The waxy wheat line K107Wx1 developed by treating ‘Kanto 107’ seeds with ethyl methanesulphonate carries the Wx‐D1d allele. However, no molecular basis supports this nomenclature. In the present study, DNA sequence analysis confirmed that a single nucleotide polymorphism in the sixth exon of Wx‐D1 changed tryptophan at position 301 into a termination codon. Based on this sequence variation, a PCR‐based KASP marker was developed to detect this point mutation using 68 BC₈F₁ plants and 297 BC₈F₂ lines derived from the cross ‘Ningmai 14’*9/K107Wx1. Combined with codominant markers for the Wx‐A1 and Wx‐B1 alleles, waxy and non‐waxy near‐isogenic lines were distinguished. The KASP marker was efficient in identifying the mutant allele and can be used to transfer waxiness to elite lines.     

Mapping of quantitative trait loci for resistance to race 1 of Pyrenophora tritici‐repentis in synthetic hexaploid wheat

Tan spot, caused by a necrotrophic fungus Pyrenophora tritici‐repentis (Ptr), has become an important foliar disease of wheat worldwide. Effective control of tan spot can be achieved by deployment of resistant wheat cultivars. An F_2:3 population derived from a cross between synthetic hexaploid wheat (SHW), TA4161‐L1 (moderately resistant) and susceptible winter wheat cultivar, ‘TAM105’ was evaluated with race 1 of Ptr under controlled conditions. The population was genotyped using Diversity Arrays Technology (DArT). Presence of transgressive segregants indicated contribution of positive alleles from both parents. Two major QTLs were located on the short arm of chromosomes 1A and 6A and designated as QTs.ksu‐1A and QTs.ksu‐6A, respectively. Two additional QTLs were identified on chromosome 7A. Resistant alleles of all the QTLs were contributed by TA4161‐L1. Novel QTLs on 6A and 7A can be a valuable addition to known resistance genes and utilized in breeding programmes to produce highly resistant cultivars.     

Role of male-sterile cytoplasm in resistance to barley yellow mosaic virus and Fusarium head blight in barley

Two types of male‐sterile cytoplasm, designated msm1 and msm2, in barley were investigated to determine whether these cytoplasms confer resistance to barley yellow mosaic virus (Ba YMV) and Fusarium head blight (FHB). Alloplasmic lines and isogenic lines of two cultivars showed the same reaction to each Ba YMV as that of their euplasmic lines. This demonstrates that the barley male‐sterile cytoplasms msm1 and msm2 have no effect on resistance to BaYMV. No significant difference in reactions to FHB was recognized among fertile alloplasmic lines of ‘Adorra’, but the difference in reactions to FHB between fertile and sterile isogenic lines of ‘Adorra’ was significant. The damage caused by FHB in the male‐sterile lines that produced sterile pollen was significantly greater than the damage in a sterile line that did not produce pollen. These results suggest that pollen or anthers are important factors in infection with or spread of FHB. For production of hybrid seeds, male‐sterile lines with no pollen production, such as those with msm1 male‐sterile cytoplasm, would reduce FHB infestation.     

Powdery mildew resistance in Czech and Slovak barley cultivars

Fifteen powdery mildew resistance genes and the gene MlaN81 derived from ‘Nepal 81’were found in 76 Czech and Slovak spring and winter barley cultivars when tested for reaction to a set of powdery mildew isolates. Nine cultivars (‘Donum’, ‘Expres’, ‘Jubilant’, ‘Orbit’, ‘Primus’, ‘Progres’, ‘Stabil’, ‘Vladan’ and ‘Zlatan’) are composed of lines with different resistance genes. The Mlat gene is present in nine cultivars and was transferred from the Anatolian landrace ‘A‐516′. The resistances derived from ‘KM‐1192’and ‘CI 7672’were identical and designated Ml(Kr). Five winter barley cultivars possess the Ml(Bw) resistance. The winter barley line ‘KM‐2099’carries the mlo gene. The parental cultivar ‘Palestine 10’was also tested in which the genes Mlk1, MlLa were identified. The German cultivar ‘Salome’, a parent of seven cultivars tested, probably carries the gene MlLa in addition to mlo and Mla7. The gene mlo6 may be present in the cultivar ‘Heris’. Most of the results were confirmed by the pedigrees of the cultivars.