QTL analysis of crown rust resistance in perennial ryegrass under conditions of natural and artificial infection

Crown rust is an economically devastating disease of perennial ryegrass. Both artificial crown rust inoculations, with the possibility of several selection cycles in one year, as well as marker-assisted selection can be used for more efficient breeding of new resistant cultivars. The objective of this study was to map quantitative trait loci (QTL) for response to crown rust infection in perennial ryegrass. In order to identify relevant markers for response to crown rust infection, QTL mapping was performed on a ryegrass mapping population which was evaluated for resistance in the field for two years as well as by artificial pathogen inoculations using a detached leaf assessment. The broad sense heritability values for the field, detached leaf and combined assays were 0.42, 0.56, and 0.64, respectively, indicating a good potential for selection for crown rust resistance. A total of six QTLs were identified and mapped to linkage groups (LG) LG1, LG4 and LG5, explaining between 6.8% and 16.4% of the total phenotypic variation.     

Mapping of the apple powdery mildew resistance gene Pl1 and its genetic association with an NBS-LRR candidate resistance gene

Molecular markers for the major apple powdery mildew resistance gene Pl1 were identified and are presently used in marker-assisted selection in apple breeding. However, the precise map position of the Pl1 gene in the apple genome was not known. The objectives of this investigation were the identification of the Malus linkage group (LG) carrying the Pl1 locus, mapping of the resistance gene by simple sequence repeat (SSR) markers, and the analysis of genetic associations between the Pl1 gene and the numerous NBS-LRR resistance gene candidates already mapped in the apple genome. A two-step linkage mapping was used, based on two different apple families. The identification of LG 12 carrying Pl1 was performed indirectly by mapping the SCAR marker AT20 in an apple progeny for which there was a core genetic map but no mildew data available. Then, the position of Pl1 on LG 12 was determined by SSR markers in a second population which has been scored for mildew over 6 years in a greenhouse and in the field. The SSR Hi07f01, previously mapped on LG 12 [Tree Genet. Genomes, 2 (2006), 202] cosegregated with AT20 and was closely linked (∼1 cM) to the Pl1 gene. The TIR-NBS-LRR resistance gene analogue 15G11 mapped by the SSCP technique was also closely linked to the Pl1 resistance locus and might be a candidate for Pl1 itself, a second powdery mildew major resistance gene ( Pld , [Theor. Appl. Genet., 110 (2004), 175]), or two scab resistance genes ( Vg , [IOBC/WPRS Bull., 23 (2000), 245]; Vb , [Genome, 49 (2006), 1238]) which all seem to be located in a common R gene cluster at the distal end of apple LG 12.     

Mapping a new source of resistance to powdery mildew in mungbean

Both restriction fragment length polymorphism (RFLP) and amplified fragment length polymorphism (AFLP) analyses were employed to map a new source of resistance to powdery mildew in mungbean. Disease scores of an F₂ population derived from the cross between a moderately resistant breeding line VC1210A and a susceptible wild relative (Vigna radiata var. sublobata, accession TC1966) showed a continuous distribution and was treated as a quantitative trait. Although no significant quantitative trait loci (QTL) that can explain the variation was detected by QTL analysis based on the reconstructed RFLP linkage map, new marker loci associated with resistance were discovered by AFLP analysis. The RFLP loci detected by two of the cloned AFLP bands are associated with resistance and constitute a new linkage group. A major resistance quantitative trait locus was found on this linkage group that accounted for 64.9% of the variation in resistance to powdery mildew. One of the probes developed in this study has the potential to assist in breeding for powdery mildew resistance in mungbean.     

Short Communication Comparison between QTL analysis of powdery mildew resistance in barley based on detached primary leaves and on field data

A quantitative trait loci (QTL) analysis of quantitative powdery mildew resistance was performed on 216 doubled haploid lines derived from a cross between the winter-barley varieties ‘Igri’ and ‘Danilo’ using 67 RFLP loci. Resistance to powdery mildew was determined in the field with natural infection and on detached primary leaves with a specific isolate. The major QTL found in both sets of analysis mapped to the same chromosomal region. No further QTL could be found in the analysis based on detached leaves and one additional minor QTL was found in the analysis based on field data.     

Potential for effective marker-assisted selection of three quantitative trait loci conferring adult plant resistance to powdery mildew in elite wheat breeding populations

Three quantitative trait loci (QTL) associated with adult plant resistance (APR) to powdery mildew (Blumeria graminis) in wheat (Triticum aestivum) cultivar ‘Massey’ were mapped in a previous study. The three QTL were located on chromosomes 2A, 2B and 1B, and explained 50% of the total phenotypic variation. A 293 recombinant inbred line (RIL) breeding population (UJ) derived from the cross of ‘USG 3209’, a derivative of ‘Massey’, and ‘Jaypee’ was used to evaluate the potential effectiveness of marker‐assisted selection (MAS) for APR. Powdery mildew severities of the 293 UJ RILs were evaluated in 2002 (F_{5 : 6}) and 2003 (F_{6 : 7}) under natural disease pressure in the field. The 293 RILs were also evaluated for disease severity in a 2004 (F_{7 : 8}) greenhouse experiment using a composite of five different isolates of B. graminis. Selection of RILs possessing the QTL on chromosome 2A, and to a lesser extent, the one on chromosome 1B was effective in identifying powdery mildew resistance in both greenhouse and field experiments. Overall, selecting RILs with QTL on chromosomes 2A and 2B was most successful in identifying highly resistant RILs, which had mean mildew severities of 4.4% and 3.2% in 2002 and 2003 field experiments, respectively. Breeders implementing MAS programs for APR to powdery mildew via selection of RILs containing the two QTL on chromosomes 2A and 2B likely will obtain RILs having high levels of resistance in the field, however combining all three QTL may ensure greater durability.     

Molecular mapping of partial resistance to powdery mildew in winter wheat cultivar Folke

The Swedish winter wheat (Triticum aestivum L.) cultivar Folke has a long record of partial and race non-specific resistance to powdery mildew (caused by Blumeria graminis f. sp. tritici) in the field. The aim of the present study was to map the main genetic factors behind the partial resistance in Folke and identify molecular markers for use in marker-assisted selection. A population of 130 recombinant inbred lines was developed from a cross between Folke and the moderately susceptible spring wheat line T2038. The population was tested for powdery mildew resistance over two years at two locations in Norway and genotyped with DArT and SSR markers. Composite interval mapping detected a total of eight quantitative trait loci (QTL) for powdery mildew resistance; six with resistance from Folke on 2BS, 2DL, 5AL, 5BS and 6BS and two with resistance from T2038 on 5BS and 7AL. None of the loci with resistance from Folke mapped to chromosomal regions with known race-specific resistance genes, which confirmed the race non-specific nature of the resistance in this cultivar. The molecular markers linked to the reported QTL will be useful as a tool for selecting partial and potentially durable resistance to powdery mildew based on the resistance in Folke.     

A major QTL effect controlling resistance to powdery mildew in winter wheat at the adult plant stage

Powdery mildew is one of the major diseases of wheat in regions with a maritime or semi‐continental climate which can strongly affect grain yield. The objective of the study was to identify and compare quantitative resistance to powdery mildew of line RE9001 at the adult plant and vernalized seedling stages. RE9001 has no known Pm gene and shows a high level of adult plant resistance in the field. Using 104 recombinant inbred lines (RILs) of an RE9001 × ‘Courtot’ F8 population, a genetic map was developed with 363 markers distributed over 26 linkage groups and covering 3825 cM. The global map density was 1 locus/10.3 cM. RILs were assessed under field and tunnel greenhouse conditions for 2 years in two locations. Eleven quantitative trait loci (QTL) were detected at the adult stage and they explained 63% of the variation, depending on the environment. Three QTLs were found, at least, in the two environments. One QTL from RE9001, mapped on chromosome 2B, was stable in each environment. This QTL, QPm.inra.2B, explained 10.3–36.6% of the variation and could be mapped in the vicinity of the Pm6 gene. At the vernalized seedling stage, one QTL detected by the isolate 93‐27 could be an allele of the Pm3g gene present in ‘Courtot’. No residual effect of the Pm3g gene was detected at either stage. Markers flanking the QTL 2B could be useful tools to combine resistance to powdery mildew in wheat cultivars.     

Phenotypic and QTL analyses of herbage production-related traits in perennial ryegrass (<Emphasis Type="Italic">Lolium perenne</Emphasis> L.)

Phenotypic and genetic evaluation of morphological traits associated with herbage biomass production was undertaken in a perennial ryegrass (Lolium perenne L.) biparental F₁ mapping population (n = 200) with parent plants from cultivars ‘Grasslands Impact’ and ‘Grasslands Samson’. Morphological traits measured on three clonal replicates of the parental genotypes and 200 F₁ progeny in a glasshouse in two separate trials (autumn and spring) included: dry weight (DW), leaf elongation rate (LER), initial tiller number (TNs), final tiller number (TNe), site filling (Fs), tiller weight (TW), leaf lamina length, leaf tip and ligule appearance rates (ALf, ALg) and leaf elongation duration (LED). Principal component analysis of patterns of trait association identified negative correlation between TNs or TNe, and TW as the primary basis for morphological difference and indicated that either high LER or long LED could reduce TN. Plants with higher LER tended to have increased DW. Quantitative trait loci (QTL) were detected on all seven linkage groups (LG) of a perennial ryegrass linkage map for all but three traits. A total of 61 QTL were identified, many of which clustered at 15 shared genome locations. Significant genotype by environment effects were encountered, evidenced both by variation between experiments in genotype rankings and by a general lack of commonality for QTL for the same traits in the different experiments. Only five QTL, for ALf, ALg and TN, were conserved between autumn and spring trials. A QTL for TN and DW on LG6 is a strong candidate for application of MAS in future plant improvement work and was found to be co-linear with QTL for equivalent traits reported on chromosome 2 in rice.     

Powdery mildew resistance gene (<Emphasis Type="Italic">Pm</Emphasis>-<Emphasis Type="Italic">AN</Emphasis>) located in a segregation distortion region of melon LGV

Powdery mildew is one of the most important melon pathogens all over the world. So far, many genes conferring resistance to powdery mildew of melon have been described, but few of these have been finely mapped or cloned. Two F₂ populations derived from Ano2 × Hami413 and Ano2 × Queen were used to map the powdery mildew resistance gene by methods of Bulked Segregation Analysis (BSA), comparative genomics and Resistance Gene Analogues (RGA) mapping. It was found that the resistance to powdery mildew in Ano2 was conferred by a dominant gene, and the gene was named Pm-AN. The genetic analysis revealed that Pm-AN located between two codominant markers RPW and MRGH63B in linkage groupV. The genetic distances between Pm-AN and these two markers were 1.4–1.8 and 1.6–2 cM. No recombination was found between Pm-AN and markers ME/E1, SRAP23. Pm-AN was located in a RGA-rich region and cosegregated with the RGA marker MRGH5 and the resistance gene Vat. Synteny analysis showed that markers in this region were collinear between melon and cucumber. Segregation distortion was found in this region using both Ano2 × Hami413 and Ano2 × Queen F₂ populations, and the distortion was more distinct in Ano2 × Hami413 F₂ population. The center of segregation distortion was located in the RGA rich region harboring Pm-AN.     

Mapping powdery mildew resistance gene in V97‐3000 soybean

V97‐3000 is a maturity group (MG) V soybean breeding line derived from SS 516 × V90‐2592 (Vance × V81‐1325) with high stachyose, small seed and powdery mildew resistance. A total of 53 F_2:3 families were derived from a cross between V97‐3000 and a powdery mildew susceptible line V99‐5089. The 53 F_2:3 families, each with 30 plants, were grown in the greenhouse for powdery mildew evaluation, and the corresponding 53 F₂ plants were genotyped using simple sequence repeat (SSR) markers. Results showed that the 53 F_2:3 families segregated in ratio of one resistant : two segregating : one susceptible (13 : 26 : 14) and the 26 segregating F_2:3 families each exhibited a good fit to three resistant : one susceptible, indicating that resistance to powdery mildew is conditioned by a single dominant gene. The gene for powdery mildew resistance in V97‐3000 was mapped on chromosome 16 [linkage group (LG) J] flanked by Satt547 and Sat_396 on one side and Sat_393 on the other side with 3.8 cM and 3.9 cM distance, respectively. This study provides a new source of powdery mildew resistance and information of genetic location of the resistance gene and linked markers, which is useful for breeders selecting powdery mildew resistance through marker‐assisted selection (MAS) in soybean breeding programmes.     

Seed yield in perennial ryegrass (<Emphasis Type="Italic">Lolium perenne</Emphasis> L.): comparative importance of component traits and detection of seed-yield-related QTL

The aims of our study were to evaluate relationships amongst morphological traits associated with seed production in a perennial ryegrass biparental population and to identify genomic regions associated with phenotypic variation in those traits using QTL analysis. This was achieved using data from two field experiments at Palmerston North and Lincoln, New Zealand, in 2003, and days to heading (DTH), reassessed in 2004. Trait association was determined for the Palmerston North experiment where measured traits included seed yield per plant (SYPlant), seed yield per spike (SYSp), reproductive tiller number (RTiller), spikelets per spike (SpktSp), florets per spikelet (FSpkt), 1000 seed weight (TSW), spike length (SpLen), florets per spike (FSp), floret site utilization (FSUtil), spread of heading (SOH) and plant growth habit (PGHabit). Traits contributing to SYPlant in order of descending value were FSpkt, FSUtil, and RTiller. High TSW was only weakly linked to SYPlant. FSUtil, SOH and RTiller were identified as valuable breeding targets for improving seed yield potential in perennial ryegrass. QTL were identified for all traits except for RTiller. QTL for SYPlant occurred on linkage groups (LG) 2 and 6. Both were co-located with QTL for SYSp and sets of SYPlant components or related traits (FSpkt, FSp; FSUtil and TSW). Major QTL for DTH were identified on LG2 and LG4 and minor QTL on LG7 in consecutive years. There was a strong genotype-by-environment interaction for SYPlant that was reflected in a lack of consistent QTL across environments, while QTL for SYSp and DTH were stable across environments. Identification of component traits and QTL important for seed yield may accelerate genetic improvement in perennial ryegrass through conventional and marker-assisted breeding, respectively.     

The resistance to leaf rust and powdery mildew of recombinant lines of barley (Hordeum vulgare L.) derived from H. vulgare × H. bulbosum crosses

A set of 23 recombinant lines (RLs) of barley ( Hordeum vulgare L.) derived from H. vulgare  ×  H. bulbosum L. crosses was inoculated with barley leaf rust ( Puccinia hordei ) and powdery mildew ( Blumeria graminis f.sp. hordei ) at the seedling stage to identify their levels and mechanisms of resistance. Eight RLs were studied further in glasshouse and field tests. All three barley parents ('Emir', 'Golden Promise' and 'Vada') were highly susceptible to powdery mildew and leaf rust isolates. Several RLs showed partial resistance expressed as high relative latency periods and low relative infection frequencies against leaf rust. This high level of partial resistance was due to a very high level of early aborting colonies without host cell necrosis. Several RLs showed hypersensitive resistance to some or all isolates. For powdery mildew, one RL was completely resistant to the CC1 isolate and had a hypersensitive resistance to the CO-02 isolate. Three RLs derived from 'Emir' were completely resistant to both powdery mildew isolates, and three more RLs tested in the field had higher levels of partial resistance than their parents. The results indicate that H. bulbosum contains major and minor gene(s) for resistance to leaf rust and powdery mildew that can be transferred to cultivated barley.     

Mapping and validation of QTLs for resistance to an Indian isolate of Ascochyta blight pathogen in chickpea

Ascochyta blight (AB) caused by Ascochyta rabiei, is globally the most important foliar disease that limits the productivity of chickpea (Cicer arietinum L.). An intraspecific linkage map of cultivated chickpea was constructed using an F₂ population derived from a cross between an AB susceptible parent ICC 4991 (Pb 7) and an AB resistant parent ICCV 04516. The resultant map consisted of 82 simple sequence repeat (SSR) markers and 2 expressed sequence tag (EST) markers covering 10 linkage groups, spanning a distance of 724.4 cM with an average marker density of 1 marker per 8.6 cM. Three quantitative trait loci (QTLs) were identified that contributed to resistance to an Indian isolate of AB, based on the seedling and adult plant reaction. QTL1 was mapped to LG3 linked to marker TR58 and explained 18.6% of the phenotypic variance (R ²) for AB resistance at the adult plant stage. QTL2 and QTL3 were both mapped to LG4 close to four SSR markers and accounted for 7.7% and 9.3%, respectively, of the total phenotypic variance for AB resistance at seedling stage. The SSR markers which flanked the AB QTLs were validated in a half-sib population derived from the same resistant parent ICCV 04516. Markers TA146 and TR20, linked to QTL2 were shown to be significantly associated with AB resistance at the seedling stage in this half-sib population. The markers linked to these QTLs can be utilized in marker-assisted breeding for AB resistance in chickpea.     

Mapping QTL for resistance to botrytis grey mould in chickpea

Botrytis grey mould (BGM) caused by Botrytis cinerea Pers. ex. Fr. is the second most important foliar disease of chickpea (Cicer arietinum L.) after ascochyta blight. An intraspecific linkage map of chickpea consisting of 144 markers assigned on 11 linkage groups was constructed from recombinant inbred lines (RILs) of a cross that involved a moderately resistant kabuli cultivar ICCV 2 and a highly susceptible desi cultivar JG 62. The length of the map obtained was 442.8 cM with an average interval length of 3.3 cM. Three quantitative trait loci (QTL) which together accounted for 43.6% of the variation for BGM resistance were identified and mapped on two linkage groups. QTL1 explained about 12.8% of the phenotypic variation for BGM resistance and was mapped on LG 6A. It was found tightly linked to markers SA14 and TS71rts36r at a LOD score of 3.7. QTL2 and QTL3 accounted for 9.5 and 48% of the phenotypic variation for BGM resistance, respectively, and were mapped on LG 3. QTL 2 was identified at LOD 2.7 and flanked by markers TA25 and TA144, positioned at 1 cM away from marker TA25. QTL3 was a strong QTL detected at LOD 17.7 and was flanked by TA159 at 12 cM distance on one side and TA118 at 4 cM distance on the other side. This is the first report on mapping of QTL for BGM resistance in chickpea. After proper validation, these QTL will be useful in marker-assisted pyramiding of BGM resistance in chickpea.     

Quantitative trait loci mapping for biomass yield traits in a Lolium inbred line derived F2 population

Lolium perenne L. (perennial ryegrass) is the principle forage grass species in temperate agriculture. Improving biomass yield still remains one of the most important aims of current forage breeding programmes. A quantitative trait locus (QTL) study investigating biomass yield traits in perennial ryegrass was carried out in greenhouse and field environments. The study is based on an F₂ population consisting of 360 individuals derived from two inbred grandparents where the F₁ has a large biomass yield phenotype. For both experimental environments co-localized QTL for biomass yield traits including fresh and dry weight and dry matter were identified on linkage groups 2, 3 and 7. A major QTL for fresh and dry weight was identified on LG 3 which explained around 30% of the phenotypic variance in the field experiment. The findings of this study are discussed with regard for their potential in research and breeding.     

1BL/1RS易位对小麦产量性状和白粉病抗性的影响及其QTL分析

用PH82-2/内乡188杂交后代240个F_5:6家系,按照α-lattice设计,分别种植在安阳、焦作和泰安,对产量和抗白粉病等性状进行了考察。利用SSR和蛋白标记对群体进行部分连锁作图,分析1BL/1RS易位对产量及其相关性状的遗传效应。结果表明,1BL/1RS易位系对产量、穗数/m²和抽穗期的影响不显著;易位系的千     

Inheritance of quantitative resistance to downy mildew (Plasmopara halstedii) in sunflower (Helianthus annuus L.)

Quantitative resistance to sunflower downy mildew was studied on inbred lines and hybrids not carrying efficient major gene resistance, in field trials in one to four sites over 3 years. Hybrids from factorial crosses showed that inheritance is under additive control and comparison with reactions of parental inbred lines gave narrow sense heritabilities of 27–57%. Analysis of a polymorphic recombinant inbred line population without efficient major gene resistance indicated that two highly significant Quantitative Trait Loci (QTL) explained 42% of variation in field reaction to downy mildew. These QTL were mapped on linkage groups 8 and 10, and do not appear related to any of the known major resistance gene clusters. Possible bases of this type of resistance and its use in breeding are discussed.     

The use of wild relatives in crop improvement: a survey of developments over the last 20 years

Hypersensitive, race specific genes primarily have been deployed to control powdery mildew (Blumeria graminis (DC) EO Speer f. sp. tritici) in wheat (Triticum aestivum L.); however, recent efforts have shifted to breeding for more durable resistance. Previously, three quantitative trait loci (QTL) for adult plant resistance (APR) to powdery mildew in the winter wheat cultivar Massey were identified in a Becker/Massey (BM) F _2:3 population. Fourteen new simple sequence repeat (SSR) markers were added to the pre-existing BM F _2:3 linkage maps near the QTL for APR on chromosomes 1BL (QPm.vt-1BL), 2AL (QPm.vt-2AL), and 2BL (QPm.vt-2BL). Genetic linkage maps comprised of 17 previously and newly mapped SSRs from the BM population on chromosomes 1BL, 2AL, and 2BL were constructed in a USG 3209/Jaypee (UJ) F _6:7 recombinant inbred line (RIL) confirmation population, wherein the APR resistance of USG 3209 was derived from Massey. Interval mapping analysis of mildew severity data collected in 2002 (F _5:6) and 2003 (F _6:7) field experiments with marker genotypic data obtained in 2003 (F _6:7) confirmed the presence of the three QTL governing APR to powdery mildew in the UJ RILs. The QTL QPm.vt-1BL, QPm.vt-2AL, and QPm.vt-2BL explained 12–13, 59–69, and 22–48% of the phenotypic variance for powdery mildew severity in the UJ confirmation populations, respectively, in two field experiments. The current study verified that the elite wheat cultivar USG 3209 possesses the same QTL for APR as its parent Massey.     

Inheritances and location of powdery mildew resistance gene in melon Edisto47

Powdery mildew caused by Podosphaera xanthii is a major disease in melon. Here we report two Px race 1 strains named Px1A and Px1B in Xinjiang, which have different pathogenicities. The more pathogenic Px1B made some powdery mildew resistant genes on linkage group V (LGV) lose their resistant traits. The inheritances of resistance to Px1A and Px1B in melon Edisto47 were studied using a BC₁ population derived from a cross between the resistant genotype Edisto47 and the susceptible cultivar Queen. The resistance/susceptibility segregation ratios observed in the Px1A-inoculated BC₁ population and the loci of polymorphic markers indicated that resistance to Px1A was controlled by two dominant genes. Quantitative trait locus analysis identified two loci mapped on LGII and LGV, respectively, for powdery mildew resistance. However, for resistance to Px1B, Edisto47 was found to bear one dominant gene. A genetic linkage map was constructed using the Px1B-inoculated BC₁ population to map the resistant gene. Comparative genomic analyses revealed that the linkage map of Pm-Edisto47-1 was collinear with the corresponding genomic region of the melon chromosome 2. Genetic analysis showed that Pm-Edisto47-1 was located between simple sequence repeat (SSR) markers CMGA36 and SSR252089, at a genetic distance of 2.1 cM to both markers. Synteny analysis showed that two genes named MELO3C015353 and MELO3C015354 were predicted as candidates for Edisto47-1 in this region.     

普通小麦白粉病成株抗性的QTL分析

以抗白粉病的日本小麦品种Fukuho-komugi和以色列小麦Oligoculm杂交F₁的DH（doubled haploid）群体107个系为材料，利用313个SSR标记和37个RFLP标记，对Fukuho-komugi和Oligoculm的白粉病成株抗性进行QTL分析。试验材料于2003－2004年度种植在北京、2003－2004和2004－2005年度种植在安阳，调查白粉病发病情况。构建了由350个位点组成的遗传连锁图，覆盖小麦21个连锁群，全长3 101 cM。采用复合区间作图法进行白粉病成株抗性QTL分析，在1A、2B、4B和7D上发现4个抗白粉病QTL，分别解释13.6%、6.6%、8.9%和12.7%的表型变异。抗白粉病基因及其紧密连锁分子标记的发掘，将为小麦抗白粉病育种的分子标记辅助选择提供理论和技术支持。