QTL mapping of a partial resistance to the corn delphacid‐transmitted viruses in Lepidopteran‐resistant maize line Mp705

A partial resistance to maize mosaic virus (MMV) and maize stripe virus (MStV) was mapped in a RILs population derived from a cross between lines MP705 (resistant) and B73 (susceptible). A genetic map constructed from 131 SSR markers spanned 1399 cM with an average distance of 9.6 cM. A total of 10 QTL were detected for resistance to MMV and MStV, using composite interval mapping. A major QTL explaining 34–41% of the phenotypic variance for early resistance to MMV was detected on chromosome 1. Another major QTL explaining up to 30% of the phenotypic variation for all traits of resistance to MStV was detected in the centromeric region of chromosome 3 (3.05 bin). After adding supplementary SSR markers, this region was found to correspond well to the one where a QTL of resistance to MStV already was located in a previous mapping study using an F₂ population derived from a cross between Rev81 and B73. These results suggested that these QTL of resistance to MStV detected on chromosome 3 could be allelic in maize genome.     

Genetic analysis of falling number in three bi‐parental common winter wheat populations

The objective of the present study was to analyse the genetic basis of falling number in three winter wheat populations. Samples for falling number determination for each population originated from at least three test environments that were free from the occurrence of preharvest sprouting at harvest time. Quantitative trait locus (QTL) analysis employing falling number values from single environments identified eight, five and three QTL in the populations Dream/Lynx, Bussard/W332‐84 and BAUB469511/Format, respectively. A major QTL common to all three populations and consistently detected in each environment mapped to the long arm of chromosome 7B. The QTL was located to a similar genomic region as the previously described major QTL for high‐isoelectric point α‐amylase content. The T1BL.1RS wheat‐rye translocation and the dwarfing gene Rht‐D1 segregating in Dream/Lynx and BAUB469511/Format were found to be important factors of falling number variation. In both populations, the presence of Rht‐D1b or the absence of T1BL.1RS increased falling number. The results indicate that late maturity α‐amylase, responsible for low falling numbers, has now been documented in German wheat germplasm.     

普通小麦辉县红-荆州黑麦异染色体系的选育及其梭条花叶病抗性鉴定

为发掘和利用荆州黑麦所携抗梭条花叶病基因，综合利用分子细胞遗传学与分子标记技术结合多年抗性鉴定，从高感梭条花叶病小麦地方品种辉县红与荆州黑麦杂交后代（F₇~F₉）中选育出二体异附加系5个(分别添加1R、2R、R3、5R和R7)、5RS端二体异附加系1个和多重异附加代换系2个（染色体组成分别为20’’+2R(2D)’’+4R’’和19’’+1R（1B）’’+2R（2B）’’+4R’’）。鉴定表明，双二倍体荆辉1号高抗梭条花叶病，表明黑麦抗性基因可在小麦背景中稳定表达，2R、R7二体异附加系及2个含2R的多重异附加代换系均表现高抗，推测2R和R7上可能携带抗病基因。这些材料是研究荆州黑麦抗性基因遗传及小麦抗病育种的新种质。     

Alleles on the two dwarfing loci on 4B and 4D are main drivers of FHB‐related traits in the Canadian winter wheat population “Vienna” × “25R47”

Fusarium head blight (FHB), leaf rust and stem rust are among the most destructive wheat diseases. High‐yielding, native disease resistance sources are available in North America. The objective of this study was to map loci associated with FHB traits, leaf rust, stem rust and plant height in a “Vienna”/”25R47” population. DArT markers were used to generate a genetic map, and quantitative trait loci (QTL) analysis was performed by evaluating 113 doubled haploid lines across three environments in Ontario, Canada. FHB resistance QTL were identified on chromosomes 4D, 4B, 2D and 7A, while a QTL for leaf and stem rust resistance was identified on chromosome 1B. The dwarfing alleles of both Rht‐B1 and Rht‐D1 were associated with increased FHB index and DON content.     

Comparative study of the structure of chromosome 1R derived from Secale montanum and Secale cereale

We produced 15 dissection lines of common wheat carrying segments of chromosome 1R of wild rye (Secale montanum) (1R^m) by the gametocidal system. Using the 1R^m dissection lines and previously established 24 dissection lines of chromosome 1R from cultivated rye (Secale cereale cv. ‘Imperial’) (1Rⁱ), we conducted cytological mapping of 97 markers that were amplified in the 1Rⁱ addition line. Sixty‐eight of the 97 markers were amplified in the 1R^m addition line. To reveal what structural differentiation occurred in chromosome 1R during domestication, we compared the cytological map of chromosome 1Rⁱ with that of chromosome 1R^m, and also with the previously published cytological map of chromosome 1R from wheat cultivar ‘Burgas 2’ (1R^B). There was one discrepancy in marker order in the satellite region between chromosomes 1Rⁱ and 1R^B, while there were four discrepancies in marker order between chromosomes 1Rⁱ and 1R^m. These results suggested that during the domestication of rye, some intrachromosomal rearrangements had occurred in chromosome 1R, although this chromosome is regarded as the most stable chromosome in the rye genome.     

Identification of QTL controlling high levels of partial resistance to Fusarium solani f. sp. pisi in pea

Fusarium root rot is a common biotic restraint on pea yields, and genetic resistance is the most feasible method for improving pea production. This study was conducted to discover quantitative trait loci (QTL) controlling genetic partial resistance to Fusarium root rot caused by Fusarium solani (Mart.) Sacc. f.sp. pisi (F.R. Jones) W.C. Snyder & H.N. Hans (Fsp). A RIL population was screened in a Fusarium root rot field disease nursery for 3 years. Composite interval mapping was employed for QTL detection using the means of disease severity from three growing seasons. Five QTL were identified, including one QTL identified in all three years. The multiyear QTL Fsp‐Ps2.1 contributed to a significant portion of the phenotypic variance (22.1–72.2%), while a second QTL, Fsp‐Ps6.1, contributed 17.3% of the phenotypic variance. The other single growing season QTL are of additional interest as they colocate with previously reported pea–Fusarium root rot resistance QTL. QTL Fsp‐Ps2.1, Fsp‐Ps3.1, Fsp‐4.1 and Fsp‐Ps7.1 are flanked by codominant SSRs and may be useful in marker‐assisted breeding of pea for high levels of partial resistance to Fsp.     

Wheat streak mosaic virus resistance in eight wheat germplasm lines

Wheat streak mosaic virus (WSMV) is a destructive pathogen in wheat (Triticum aestivum L.). Host resistance is the most effective way to control this virus. To date, Wsm2 is the only wheat resistance gene that is genetically mapped. The objective of this study was to identify germplasm lines that might carry resistance genes different from Wsm2. Eight newly reported resistant germplasm lines were examined by allelic tests. To validate the allelic test results, five of them were further analysed for the inheritance of WSMV resistance. A Wsm2‐linked marker was also genotyped on populations developed for the inheritance study. Our results suggested that the WSMV resistance in lines CItr9358, PI225288, PI243652, PI245439, PI245526 and PI478095 was controlled by either Wsm2 or a gene very closely linked to Wsm2. The resistance in PI243753 and PI321730, however, is likely controlled by a gene different from, but linked to Wsm2. The resistance in PI321730 might also involve some minor genes. This study provided useful information for breeders to select appropriate resistant lines to improve WSMV resistance in wheat.     

The potential of genomic‐assisted breeding to improve Fusarium head blight resistance in winter durum wheat

Durum wheat is the most important tetraploid wheat mainly used for semolina and pasta production, but is notorious for its high susceptibility to Fusarium head blight (FHB). Our objectives were to identify and characterize quantitative trait loci (QTL) in winter durum and to evaluate the potential of genomic approaches for the improvement of FHB resistance. Here, we employed an international panel of 170 winter and 14 spring durum lines, phenotyped for Fusarium culmorum resistance at five environments. Heading date, plant height and mean FHB severity showed significant genotypic variation with high heritabilities and FHB resistance was negatively correlated with both heading date and plant height. The dwarfing gene Rht‐B1 significantly affected FHB resistance and the genome‐wide association scan identified eight additional QTL affecting FHB resistance, explaining between 1% and 14% of the genotypic variation. A genome‐wide prediction approach yielded only a slightly improved predictive ability compared to marker‐assisted selection based on the four strongest QTL. In conclusion, FHB resistance in durum wheat is a highly quantitative trait and in breeding programmes may best be tackled by classical high‐throughput recurrent phenotypic selection that can be assisted by genomic prediction if marker profiles are available.     

Development and characterization of a <Emphasis Type="Italic">Triticum aestivum</Emphasis>-<Emphasis Type="Italic">Haynaldia villosa</Emphasis> translocation line T4VS⋅4DL conferring resistance to wheat spindle streak mosaic virus

Previous studies showed that a T. aestivum-H. villosa disomic substitution line DS4V(4D) showed a high level of resistance to wheat spindle streak mosaic virus (WSSMV). By crossing DS4V(4D) with the common wheat variety Yangmai #5, plants were obtained that were double monosomic for chromosomes 4V and 4D. Univalents are prone to misdivision at the centromere, and fusion of the derived telocentric chromosomes leads to the production of Robertsonian whole-arm translocations. We screened the progenies of such double monosomic plants by C-banding and genomic in situ hybridization and identified one compensating translocation where the short arm of 4V was translocated to the long arm of 4D of wheat, T4VS⋅4DL. RFLP analysis using the group-4 specific probe BCD110 was used to confirm the translocation. The T4VS⋅4DL translocation stock, accessioned as NAU413, is highly resistant to WSSMV and is also of good agronomic type. The WSSMV resistance gene located on 4VS was designated Wss1.     

RNAi‐based Bean golden mosaic virus‐resistant common bean (Embrapa 5.1) shows simple inheritance for both transgene and disease resistance

Bean golden mosaic virus (BGMV) is the causal agent of bean golden mosaic of common beans. A transgenic bean line that has been developed based on RNA interference to silence the BGMV rep gene showed immunity to the virus. Crosses were done between the transgenic line and six bean cultivars followed by four backcrosses to the commercial cultivars ‘Pérola’ and ‘BRS Pontal’. The transgene locus was consistently inherited from the crosses analysed in a Mendelian fashion in the segregating populations. The disease resistance reaction co‐inherited with the transgene. Nevertheless, the expression of disease resistance displayed a dosage effect phenomenon in the F₁ generation. The analysis of the homozygous near‐isogenic lines in field conditions, under high BGMV disease incidence, indicated that the transgenic lines were completely resistant. These results show the strength of the disease resistance obtained, the stability of the trait across generations and its usefulness in the management of a disease for which there is no reported Phaseolus germplasm with immunity.     

A QTL on chromosome 2DS of ‘Sumai 3’ increases susceptibility to <Emphasis Type="Italic">Fusarium</Emphasis> head blight in wheat

Much effort has been invested in identifying molecular markers in wheat (Triticum aestivum L.) linked to quantitative trait loci (QTL) that confer resistance to Fusarium head blight (FHB) caused by Fusarium graminearum Schwabe [teleomorph Gibberella zeae (Schwein) Petch]. Even after several generations of crossing and selection by many wheat breeding programs, resistance of the Chinese spring wheat cultivar ‘Sumai 3’ (PI 481542) remains among the most effective. It therefore seems that undocumented resistance QTL present in Sumai 3 were not detected in various mapping studies. Using an extremely susceptible Tibetan landrace (‘Y1193-6’; unknown pedigree) in the creation of a mapping population with Sumai 3, the objective of this research was to identify undocumented resistance QTL in Sumai 3. This was accomplished through collecting disease index (DI) and Fusarium damaged kernel (FDK) phenotypic values along with 305 Diversity Array Technology (DArT) and 52 Simple Sequence Repeat (SSR) marker genotypes on 160 F_2:6 recombinant inbred lines (RILs). Disease response evaluations were based on four (two greenhouse and two field) experiments where spray inoculation methods were used. Three QTL were identified on chromosome arms 3BS, 6BL and 2DS explaining 26.1, 10.7 and 18.9% of the phenotypic variation for DI, respectively. The same QTL were also significantly associated with reduced FDK scores and explained 28.0, 11.0 and 23.0% of phenotypic variation. Lines within the mapping population were placed in eight categories with respect to their various QTL combinations. Lines with no QTL were the most susceptible, whereas those with the Sumai 3-derived 3BS and 6BL QTL combined with the 2DS QTL from Y1193-6 were the most resistant. Though the 3BS and 6BL QTL are well-documented, the 2DS resistance QTL, which was contributed by the susceptible parent, confers increased susceptibility when derived from Sumai 3. In this study no new FHB QTL from Sumai 3 was discovered, but results suggest that Sumai 3 contains a QTL for susceptibility on chromosome arm 2DS. Selection against this QTL may potentially increase resistance levels among Sumai 3-derived populations.     

QTL analysis for cooking traits of super rice with a high‐density SNP genetic map and fine mapping of a novel boiled grain length locus

Hybrid rice has contributed substantially to the improvement of grain production worldwide, yet its poor cooking and tasting characteristics have long been recognized. In this study, 132 recombinant inbred lines derived from LYPJ were used to identify quantitative trait loci (QTLs) for 12 cooking traits with the high‐density SNP linkage map recently developed by our team. We identified 17 QTLs on chromosomes 1, 2, 4, 5, 6, 7, 8, 9 and 11, which accounted for 7.50% to 23.50% of the phenotypic variations. A novel major QTL qBGL7 for boiled grain length was further fine‐mapped to an interval of 440 Kb between the two markers RM21906 and gl3 using a BC₃F₂ population. Two near‐isogenic lines with extreme boiled grain length, GX5‐176 and GX5‐101, could be directly used in improving cooking quality. We also identified a QTL for soaked grain width expansion rate, qSGWE6, in the Wx gene region on chromosome 6. The Wx differential regulation coincided with sequential variation between the two parents. Our work offered a theoretical basis for molecular breeding of high‐quality hybrid rice.     

Development of gene‐based markers for the Turnip mosaic virus resistance gene retr02 in Brassica rapa

Turnip mosaic virus (TuMV) is responsible for a serious disease that affects the production of Chinese cabbage. Previous studies have cloned a series of TuMV resistance genes and developed molecular markers. In this study, a derived cleaved amplified polymorphism sequence (dCAPS) marker and a Kompetitive Allele Specific PCR (KASP) marker were developed based on a single recessive gene, retr02, which confers broad‐spectrum TuMV resistance in Chinese cabbage by means of an additional G at the junction of exon 1 and intron 1. The two markers were able to detect the retr02 allele in Chinese cabbage accessions used in breeding programmes. Compared with the dCAPS marker, the KASP marker was flexible, cost‐effective and quick to process, which is likely to be beneficial in establishing high‐throughput assays for marker‐assisted selection.     

Screening for resistance to take-all in wheat,triticale and wheat-triticale hybrid lines

Summary Fifteen triticale and wheat-triticale hybrid lines were evaluated for resistance to the take-all fungus Gaeumannomyces graminis var. tritici and compared with five wheat and two rye lines in inoculated field and pot trials. The triticale and wheat-triticale hybrid lines varied in rye chromosome number and degree of resistance expressed. One line, Venus with seven pairs of rye chromosomes consistently showed levels of resistance intermediate between wheat and rye. A trend was observed where increasing rye chromosome content led to greater resistance but exceptions showed that variation within triticales could not be ascribed to rye chromosome content alone.     

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.     

The potato R10 resistance specificity to late blight is conferred by both a single dominant R gene and quantitative trait loci

The R10 late blight differential of potato, 3681ad1, exhibits good field resistance. Progeny from the cross between 3681ad1 and the susceptible cultivar ‘Katahdin’ were assessed for late blight resistance to three Phytophthora infestans isolates, using a detached leaf assay. Progeny differed in response to the three isolates. Resistance to isolates IPO‐0 and 99018 was controlled by quantitative trait loci (QTL), whereas resistance to isolate 89148‐9 was inherited as a dominant R gene, designated as R10 in this study. Statistical analysis revealed that one of the resistance QTLs to isolates IPO‐0 and 99018 is linked to the R10 gene, which maps to chromosome 11 in a region where a complex late blight resistance locus has been reported previously. A high‐resolution map of R10 was constructed using a large segregating population, and the gene was delimited to a genetic interval of 0.26 cM. The clustering of the qualitative gene R10 with resistance QTLs could explain the field resistance observed with 3681ad1.     

A quantitative trait locus on chromosome 5B controls resistance of <Emphasis Type="Italic">Triticum turgidum</Emphasis> (L.) var. <Emphasis Type="Italic">diccocoides</Emphasis> to Stagonospora nodorum blotch

Stagonospora nodorum blotch (SNB) is an important foliar disease of durum wheat (Triticum turgidum var. durum) worldwide. The combined effects of SNB and tan spot, considered as components of the leaf spotting disease complex, result in significant damage to wheat production in the northern Great Plains of North America. The main objective of this study was the genetic analysis of resistance to SNB caused by Phaeosphaeria nodorum in tetraploid wheat, and its association with tan spot caused by Pyrenophora tritici-repentis race 2. The 133 recombinant inbred chromosome lines (RICL) developed from the cross LDN/LDN(Dic-5B) were evaluated for SNB reaction at the seedling stage under greenhouse conditions. Molecular markers were used to map a quantitative trait locus (QTL) on chromosome 5B, explaining 37.6% of the phenotypic variation in SNB reaction. The location of the QTL was 8.8 cM distal to the tsn1 locus coding for resistance to P. tritici-repentis race 2. The presence of genes for resistance to both SNB and tan spot in close proximity in tetraploid wheat and the identification of molecular markers linked to these genes or QTLs will be useful for incorporating resistance to these diseases in wheat breeding programs.     

Identification and validation of an over‐dominant QTL controlling soybean seed weight using populations derived from Glycine max × Glycine soja

Heterosis, or hybrid vigour, has been used to improve seed yield in several important crops for decades and it has potential applications in soybean. The discovery of over‐dominant quantitative trait loci (QTL) underlying yield‐related traits, such as seed weight, will facilitate hybrid soybean breeding via marker‐assisted selection. In this study, F₂ and F_2 : 3 populations derived from the crosses of ‘Jidou 12’ (Glycine max) × ‘ZYD2738’ (Glycine soja) and ‘Jidou 9’ (G. max) × ‘ZYD2738’ were used to identify over‐dominant QTL associated with seed weight. A total of seven QTL were identified. Among them, qSWT_13_1, mapped on chromosome 13 and linked with Satt114, showed an over‐dominant effect in two populations for two successive generations. This over‐dominant effect was further examined by six subpopulations derived from ‘Jidou12’ × ‘ZYD2738’. The seed weight for heterozygous individuals was 1.1‐ to 1.6‐fold higher than that of homozygous individuals among the six validation populations examined in different locations and years. Therefore, qSWT_13_1 may be a useful locus to improve the yield of hybrid soybean and to understand the molecular mechanism of heterosis in soybean.     

Validation of a major QTL for scab resistance with SSR markers and use of marker-assisted selection in wheat

The objectives of this study were to validate the major quantitative trait locus (QTL) for scab resistance on the short arm of chromosome 3B in bread wheat and to isolate near‐isogenic lines for this QTL using marker‐assisted selection (MAS). Two resistant by susceptible populations, both using ‘Ning7840’ as the source of resistance, were developed to examine the effect of the 3BS QTL in different genetic backgrounds. Data for scab resistance and simple sequence repeat (SSR) markers linked to the resistance QTL were analyzed in the F_2:3 lines of one population and in the F_3:4 lines of the other. Markers linked to the major QTL on chromosome 3BS in the original mapping population (‘Ning7840’/‘Clark’) were closely associated with scab resistance in both validation populations. Marker‐assisted selection for the QTL with the SSR markers combined with phenotypic selection was more effective than selection based solely on phenotypic evaluation in early generations. Marker‐assisted selection of the major QTL during the seedling stage plus phenotypic selection after flowering effectively identified scab resistant lines in this experiment. Near‐isogenic lines for this 3BS QTL were isolated from the F₆ generation of the cross ‘Ning7840’/‘IL89‐7978’ based on two flanking SSR markers, Xgwm389 and Xbarc147. Based on these results, MAS for the major scab resistance QTL can improve selection efficiency and may facilitate stacking of scab resistance genes from different sources.     

Mapping and validation of PCR-based markers associated with a major QTL for seed dormancy in wheat

Seed dormancy is one of the important factors controlling pre-harvest sprouting (PHS) resistance in wheat. We identified a major quantitative trait locus (QTL) for seed dormancy on the long arm of wheat chromosome 4A (4AL) via simple sequence repeat (SSR)-based genetic mapping using doubled haploid lines from a cross between Japanese PHS resistant variety ‘Kitamoe’ and the Alpine non-resistant variety “Münstertaler” (K/M). The QTL explained 43.3% of total phenotypic variation for seed dormancy under greenhouse conditions. SSR markers flanking the QTL were assigned to the chromosome long arm fraction length 0.59–0.66 on the basis of chromosome deletion analysis, suggesting that the gene(s) controlling seed dormancy are probably located within this region. Under greenhouse conditions, the QTL explained 28.5 and 39.0% of total phenotypic variation for seed dormancy in Haruyutaka/Leader (HT/L) and OS21-5/Haruyokoi (O/HK) populations, respectively. However, in field conditions, the effect was relatively low or not significant in both the K/M and HT/L populations. These markers were considered to be widely useful in common with various genetic backgrounds for improvement of seed dormancy through the use of marker-assisted selection. Further detailed research using near isogenic lines will be needed to define how this major QTL interacts with environmental conditions in our area.