Characterization of genes <Emphasis Type="Italic">Rpp2</Emphasis>, <Emphasis Type="Italic">Rpp4</Emphasis>, and <Emphasis Type="Italic">Rpp5</Emphasis> for resistance to soybean rust

Asian rust, caused by the fungus Phakopsora pachyrhizi, is the most severe disease currently threatening soybean crops in Brazil. The development of resistant cultivars is a top priority. Genetic characterization of resistance genes is important for estimating the improvement when these genes are introduced into soybean plants and for planning breeding strategies against this disease. Here, we infected an F₂ population of 140 plants derived from a cross between ‘An-76’, a line carrying two resistance genes (Rpp2 and Rpp4), and ‘Kinoshita’, a cultivar carrying Rpp5, with a Brazilian rust population. We scored six characters of rust resistance (lesion color [LC], frequency of lesions having uredinia [%LU], number of uredinia per lesion [NoU], frequency of open uredinia [%OU], sporulation level [SL], and incubation period [IP]) to identify the genetic contributions of the three genes to these characters. Furthermore, we selected genotypes carrying these three loci in homozygosis by marker-assisted selection and evaluated their genetic effect in comparison with their ancestors, An-76, PI230970, PI459025, Kinoshita and BRS184. All three genes contributed to the phenotypes of these characters in F₂ population and when pyramided, they significantly contributed to increase the resistance in comparison to their ancestors. Rpp2, previously reported as being defeated by the same rust population, showed a large contribution to resistance, and its resistance allele seemed to be recessive. Rpp5 had the largest contribution among the three genes, especially to SL and NoU. Only Rpp5 showed a significant contribution to LC. No QTLs for IP were detected in the regions of the three genes. We consider that these genes could contribute differently to resistance to soybean rust, and that genetic background plays an important role in Rpp2 activity. All three loci together worked additively to increase resistance when they were pyramided in a single genotype indicating that the pyramiding strategy is one good breeding strategy to increase soybean rust resistance.     

SSR and STS markers for wheat stripe rust resistance gene <Emphasis Type="Italic">Yr26</Emphasis>

Stripe (yellow) rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most devastating wheat diseases worldwide. Triticum aestivum-Haynaldia villosa 6VS/6AL translocation lines carrying the Yr26 gene on chromosome 1B, are resistant to most races of Pst used in virulence tests. In order to better utilize Yr26 for wheat improvement, we attempted to screen SSR and EST-based STS markers closely linked with Yr26. A total of 500 F₂ plants and the F_2:3 progenies derived from a cross between 92R137 and susceptible cultivar Yangmai 5 were inoculated with race CYR32. The analysis confirmed that stripe rust resistance was controlled by a single dominant gene, Yr26. Among 35 pairs of genomic SSR markers and 81 pairs of STS markers derived from EST sequences located on chromosome 1B, Yr26 was flanked by 5 SSR and 7 STS markers. The markers were mapped in deletion bins using CS aneuploid and deletion lines. The closest flanking marker loci, Xwe173 and Xbarc181, mapped in 1BL and the genetic distances from Yr26 were 1.4 cM and 6.7 cM, respectively. Some of these markers were previously reported on 1BS. Eight common wheat cultivars and lines developed from the T. aestivum-H. villosa 6VS/6AL translocation lines by different research groups were tested for presence of the markers. Five lines with Yr26 carried the flanking markers whereas three lines without Yr26 did not. The results indicated that the flanking markers should be useful in marker-assisted selection for incorporating Yr26 into wheat cultivars.     

Molecular mapping of <Emphasis Type="Italic">Pc68</Emphasis>, a crown rust resistance gene in <Emphasis Type="Italic">Avena</Emphasis><Emphasis Type="Italic">sativa</Emphasis>

Crown rust, which is caused by Puccinia coronata f. sp. avenae, P. Syd. & Syd., is the most destructive disease of cultivated oats (Avena sativa L.) throughout the world. Resistance to the disease that is based on a single gene is often short-lived because of the extremely great genetic diversity of P. coronata, which suggests that there is a need to develop oat cultivars with several resistance genes. This study aimed to identify amplified fragment length polymorphism AFLP markers that are linked to the major resistance gene, Pc68, and to amplify the F₆ genetic map from Pc68/5*Starter × UFRGS8. Seventy-eight markers with normal segregation were discovered and distributed in 12 linkage groups. The map covered 409.4 cM of the Avena sativa genome. Two AFLP markers were linked in repulsion to Pc68: U8PM22 and U8PM25, which flank the gene at 18.60 and 18.83 centiMorgans (cM), respectively. The marker U8PM25 is located in the linkage group 4_12 in the Kanota × Ogle reference oat population. These markers should be useful for transferring Pc68 to genotypes with good agronomic characteristics and for pyramiding crown rust resistance genes.     

Allelic variation for the rust resistance gene <Emphasis Type="Italic">Lr34</Emphasis>/<Emphasis Type="Italic">Yr18</Emphasis> in Canadian wheat cultivars

The wheat (Triticum aestivum L.) gene Lr34/Yr18 conditions resistance to leaf rust, stripe rust, and stem rust, along with other diseases such as powdery mildew. This makes it one of the most important genes in wheat. In Canada, Lr34 has provided effective leaf rust resistance since it was first incorporated into the cultivar Glenlea, registered in 1972. Recently, molecular markers were discovered that are either closely linked to this locus, or contained within the gene. Canadian wheat cultivars released from 1900 to 2007, breeding lines and related parental lines, were tested for sequence based markers caSNP12, caIND11, caIND10, caSNP4, microsatellite markers wms1220, cam11, csLVMS1, swm10, csLV34, and insertion site based polymorphism marker caISBP1. Thirty different molecular marker haplotypes were found among the 375 lines tested; 5 haplotypes had the resistance allele for Lr34, and 25 haplotypes had a susceptibility allele at this locus. The numbers of lines in each haplotype group varied from 1 to 140. The largest group was represented by the leaf rust susceptible cultivar “Thatcher” and many lines derived from “Thatcher”. The 5 haplotypes that had the resistance allele for Lr34 were identical for the markers tested within the coding region of the gene but differed in the linked markers wms1220, caISBP1, cam11, and csLV34. The presence of the resistance or susceptibility allele at the Lr34 locus was tracked through the ancestries of the Canadian wheat classes, revealing that the resistance allele was present in many cultivars released since the 1970s, but not generally in the older cultivars.     

Identification of QTL underlying soluble pigment content in soybean stems related to resistance to soybean white mold (<Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis>)

The frequency of soybean white mold (Sclerotinia sclerotiorum, SWM) outbreaks has increased since 1978, and this disease is currently considered to be the second most important cause of soybean yield loss worldwide. We have studied SWM in stems of soybean cultivar Maple Arrow, which shows partial resistance to SWM, in an attempt to identify the quantitative trait loci (QTLs) underlying soluble pigment(s) content, which is associated with SWM resistance. A SWM-susceptible cultivar, Hefeng 25, was crossed with Maple Arrow, and 149 F_5:6 recombinant inbred lines were subsequently advanced through single-seed-descent. A total of 109 simple sequence repeat (SSR) markers were used to construct a genetic linkage map. Three QTLs for soluble pigment content in soybean stems associated with the resistance to SWM, namely, Qsp-1 (Satt502-Sat_159), Qsp-2 (Sat_156-Satt251), and Qsp-3 (Satt525-Satt233), were identified in 2007 and 2008 and located onto linkage groups D1a+q, B1 and A2, respectively. The phenotypic variation (R ²) explained by these QTLs ranged from 6.29 to 15.37%. These three QTLs were not significantly related to known QTLs associated with escape resistant mechanisms. The use of these QTLs in marker-assisted selection may contribute to improved soybean resistance to SWM.     

Molecular tagging of a stripe rust resistance gene in <Emphasis Type="Italic">Aegilops tauschii</Emphasis>

Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most important diseases of common wheat (Triticum aestivum L.). China has the largest stripe rust epidemic areas in the world and yield losses can be large. Aegilops tauschii Coss, the D-genome progenitor of common wheat, includes two subspecies, tauschii and strangulata (Eig) Tzvel. The ssp. strangulata accession AS2388 is highly resistant to the prevailing physiological races of PST in China, and possesses a single dominant gene for stripe rust resistance. In order to tag this gene, AS2388 was crossed with the highly susceptible ssp. tauschii accession AS87. The parents, F₂ plants, and F_2:3 families were tested at adult plant stage in field trials with six currently prevailing races. Simple sequence repeat (SSR) primers were used to identify molecular markers linked to the resistance gene. SSR markers Xwmc285 and Xwmc617 were linked to the resistance gene on chromosome arm 4DS flanking it at 1.7 and 34.6 cM, respectively. Based on the chromosomal location, this gene temporarily designated as YrAS2388 is probably novel. The resistance in Ae. tauschii AS2388 was partially expressed in two newly developed synthetic hexaploid backgrounds.     

Development of a PCR assay and marker-assisted transfer of leaf rust resistance gene <Emphasis Type="Italic">Lr58</Emphasis> into adapted winter wheats

Leaf rust resistance gene Lr58 derived from Aegilops triuncialis L. was transferred to the hard red winter wheat (HRWW) cultivars Jagger and Overley by standard backcrossing and marker-assisted selection (MAS). A co-dominant PCR-based sequence tagged site (STS) marker was developed based on the sequence information of the RFLP marker (XksuH16) diagnostically detecting the alien segment in T2BS·2BL-2^tL(0.95). STS marker Xncw-Lr58-1 was used to select backcross F₁ plants with rust resistance. The co-dominant marker polymorphism detected by primer pair NCW-Lr58-1 efficiently identified the homozygous BC₃F₂ plants with rust resistance gene Lr58. The STS marker Xncw-Lr58-1 showed consistent diagnostic polymorphism between the resistant source and the wheat cultivars selected by the US Wheat Coordinated Agricultural Project. The utility and compatibility of the STS marker in MAS programs involving robust genotyping platforms was demonstrated in both agarose-based and capillary-based platforms. Screening backcross derivatives carrying Lr58 with various rust races at seedling stage suggested the transferred rust resistance in adapted winter wheats is stable in both cultivar backgrounds. Lr58 in adapted winter wheat backgrounds could be used in combination with other resistance genes in wheat rust resistance breeding.     

Mapping of quantitative trait loci controlling partial resistance against rust incited by <Emphasis Type="Italic">Uromyces pisi</Emphasis> (Pers.) Wint. in a <Emphasis Type="Italic">Pisum fulvum</Emphasis> L. intraspecific cross

A quantitative trait loci (QTL) associated with resistance to pea rust, caused by the fungus Uromyces pisi (Pers.) Wint., has been identified in a F₂ population derived from an intraspecific cross between two wild pea (Pisum fulvum L.) accessions, IFPI3260 (resistant) and IFPI3251 (susceptible). Both parental lines and all the segregating population displayed a fully compatible interaction (high infection type), which indicates absence of hypersensitive response. Nevertheless, differences on the percentage of symptomatic area of the whole plant (disease severity) were observed. A genetic map was developed covering 1283.3 cM and including 146 markers (144 random amplified polymorphic DNA (RAPDs) and two sequence tagged sites (STSs) markers) distributed in 9 linkage groups. A QTL explaining 63% of the total phenotypic variation was located in linkage group 3. RAPDs markers (OPY11₁₃₁₆ and OPV17₁₀₇₈) flanking this QTL should allow, after their conversion in SCARs, a reliable marker-assisted selection for rust resistance.     

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.     

Identification of RAPD markers linked to the rust (<Emphasis Type="Italic">Uromyces fabae</Emphasis>) resistance gene in pea (<Emphasis Type="Italic">Pisum sativum</Emphasis>)

Summary Two RAPD markers linked to gene for resistance (assayed as pustule number cm⁻² leaf area) to rust [Uromyces fabae (Pers.) de Bary] in pea (Pisum sativum L.) were identified using a mapping population of 31 BC₁F₁ [HUVP 1 (HUVP 1 × FC 1] plants, FC 1 being the resistant parent. The analysis of genetics of rust resistance was based on the parents, F₁, F₂, BC₁F₁ and BC₁F₂ generations. Rust resistance in pea is of non-hypersensitive type; it appeared to be governed by a single partially dominant gene for which symbol Ruf is proposed. Further, this trait seems to be affected by some polygenes in addition to the proposed oligogene Ruf. A total of 614 decamer primers were used to survey the parental polymorphism with regard to DNA amplification by polymerase chain reaction. The primers that amplified polymorphic bands present in the resistant parent (FC 1) were used for bulked segregant analysis. Those markers that amplified consistently and differentially in the resistant and susceptible bulks were separately tested with the 31 BC₁F₁ individuals. Two RAPD makers, viz., SC10-82₃₆₀ (primer, GCCGTGAAGT), and SCRI-71₁₀₀₀ (primer, GTGGCGTAGT), flanking the rust resistance gene (Ruf) with a distance of 10.8 cM (0.097 rF and LOD of 5.05) and 24.5 cM (0.194 rF and a LOD of 2.72), respectively, were identified. These RAPD markers were not close enough to Ruf to allow a dependable maker-assisted selection for rust resistance. However, if the two makers flanking Ruf were used together, the effectiveness of MAS would be improved considerably.     

A high-density integrative linkage map for <Emphasis Type="Italic">Gossypium hirsutum</Emphasis>

Sequence-related amplified polymorphism (SRAP) combined with SSRs, RAPDs, and RGAPs was used to construct a high density genetic map for a F₂ population derived from the cross DH962 (G. hirsutum accession) × Jimian5 (G. hirsutum cultivar). A total of 4,096 SRAP primer combinations, 6310 SSRs, 600 RAPDs, and 10 RGAPs produced 331, 156, 17 and 2 polymorphic loci, respectively. Among the 506 loci obtained, 471 loci (309 SRAPs, 144 SSRs, 16 RAPDs and 2 RGAPs) were assigned to 51 linkage groups. Of these, 29 linkage groups were assigned to corresponding chromosomes by SSR markers with known chromosome locations. The map covered 3070.2 cM with a mean density of 6.5 cM per locus. The segregation distortion in this population was 9.49%, and these distorted loci tend to cluster at the end of linkage groups or in minor clusters on linkage groups. The majority of SRAPs in this map provided an effective tool for map construction in G. hirsutum despite of its low polymorphism. This high-density linkage map will be useful for further genetic studies in Upland cotton, including mapping of loci controlling quantitative traits, and comparative and integrative analysis with other interspecific and intraspecific linkage maps in cotton.     

Evaluation of seedling and adult plant resistance in European wheat cultivars to Australian isolates of <Emphasis Type="Italic">Puccinia striiformis</Emphasis> f. sp. <Emphasis Type="Italic">tritici</Emphasis>

A set of 105 European wheat cultivars was assessed for seedling resistance and adult plant resistance (APR) to stripe (yellow) rust in greenhouse and field tests with selected Australian isolates of Puccinia striiformis f. sp. tritici (Pst). Twelve cultivars were susceptible to all pathotypes, and among the remainder, 11 designated seedling genes (Yr1, Yr3, Yr4, Yr6, Yr7, Yr9, Yr17, Yr27, Yr32, YrHVII and YrSP) and a range of unidentified seedling resistances were detected either singly or in combination. The identity of seedling resistance in 43 cultivars could not be determined with the available Pst pathotypes, and it is considered possible that at least some of these may carry uncharacterised seedling resistance genes. The gene Yr9 occurred with the highest frequency, present in 19 cultivars (18%), followed by Yr17, present in 10 cultivars (10%). Twenty four cultivars lacked seedling resistance that was effective against the pathotype used in field nurseries, and all but two of these displayed very high levels of APR. While the genetic identity of this APR is currently unknown, it is potentially a very useful source of resistance to Pst. Genetic studies are now needed to characterise this resistance to expedite its use in efforts to breed for resistance to stripe rust. Colin R. Wellings seconded from NSW Department of Primary Industries.     

Dominant gene for common bean resistance to common bacterial blight caused by <Emphasis Type="Italic">Xanthomonas</Emphasis><Emphasis Type="Italic">axonopodis</Emphasis> pv. <Emphasis Type="Italic">phaseoli</Emphasis>

The common bacterial blight pathogen [Xanthomonas axonopodis pv. phaseoli (Xap)] is a limiting factor for common bean (Phaseolus vulgaris L.) production worldwide and resistance to the pathogen in most commercial cultivars is inadequate. Variability in virulence of the bacterial pathogen has been observed in strains isolated from Puerto Rico and Central America. A few common bean lines show a differential reaction when inoculated with different Xap strains, indicating the presence of pathogenic races. In order to study the inheritance of resistance to common bacterial blight in common bean, a breeding line that showed a differential foliar reaction to Xap strains was selected and was crossed with a susceptible parent. The inheritance of resistance to one of the selected Xap races was determined by analysis of segregation patterns in the F₁, F₂, F₃ and F₄ generations from the cross between the resistant parent PR0313-58 and the susceptible parent ‘Rosada Nativa’. The F₁, F₂ and F₃ generations were tested under greenhouse conditions. Resistant and susceptible F_3:4 sister lines were tested in the field. The statistical analysis of all generations followed the model for a dominant resistance gene. The resistant phenotype was found to co-segregate with the SCAR SAP6 marker, located on LG 10. These results fit the hypothesis that resistance is controlled by a single dominant gene. The symbol proposed for the resistance gene is Xap-1 and for the bacterial race, XapV1.     

Mapping of QTLs detected in a <Emphasis Type="Italic">Brassica napus</Emphasis> DH population for resistance to <Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis> in multiple environments

Sclerotinia stem rot, caused by the fungus Sclerotinia sclerotiorum, is one of the most devastating diseases of rapeseed (Brassica napus L.) in China. The two major factors limiting the development of disease resistance are (1) the absence of accessions with complete resistance and (2) the lack of a single method that can be widely applied to assess tolerance—even though accessions with differential tolerance to S. sclerotiorum have been identified in China. In the study reported here, we have used one doubled haploid (DH) population consisting of 72 lines, which was derived from the F₁ generation of a cross between a partially resistant line (DH821) and a susceptible line (DHBao604), to identify quantitative trait loci (QTLs) involved in the resistance to S. sclerotiorum. Three inoculation methods, namely, mycelial toothpick inoculation (MTI), mycelial plug inoculation (MPI), and infected petal inoculation (IPI), were used to assess resistance at the adult plant stage. A genetic linkage map with 20 linkage groups covering 1746.5 cM, with an average space of 6.93 cM, was constructed using a total of 252 molecular markers, including 91 simple sequence repeats, 72 randomly amplified polymorphic DNA, 86 sequence-related amplified polymorphisms, two restriction fragment length polymorphisms, and one expressed sequence tag. Composite interval mapping identified ten, one and ten QTLs using MTI, MPI and IPI methods, respectively, at a LOD > 2.5. One QTL was detected in linkage group N12 by MTI in 2004 and 2005 and by IPI in 2005. Another QTL was detected in linkage group N3 and N4 by MPI in 2006 and 2007. There was one common QTL detected by MTI in 2005 and by MPI in 2006. These results provide information on the genetic control of resistance to S. sclerotiorum in oilseed rape.     

Identification of quantitative trait loci associated with resistance to foliar diseases in sorghum [<Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.) Moench]

Forage sorghum cultivars grown in India are susceptible to various foliar diseases, of which anthracnose, rust, zonate leaf spot, drechslera leaf blight and target leaf spot cause severe damage. We report here the quantitative trait loci (QTLs) conferring resistance to these foliar diseases. QTL analysis was undertaken using 168 F₇ recombinant inbred lines (RILs) of a cross between a female parental line 296B (resistant) and a germplasm accession IS18551 (susceptible). RILs and parents were evaluated in replicated field trials in two environments. A total of twelve QTLs for five foliar diseases on three sorghum linkage groups (SBI-03, SBI-04 and SBI-06) were detected, accounting for 6.9–44.9% phenotypic variance. The morphological marker Plant color (Plcor) was associated with most of the QTL across years and locations. The QTL information generated in this study will aid in the transfer of foliar disease resistance into elite susceptible sorghum breeding lines through marker-assisted selection.     

QTL analysis for thousand-grain weight under terminal drought stress in bread wheat (<Emphasis Type="Italic">Triticum</Emphasis><Emphasis Type="Italic">aestivum</Emphasis> L.)

Grain yield under post-anthesis drought stress is one of the most complex traits, which is inherited quantitatively. The present study was conducted to identify genes determining post-anthesis drought stress tolerance in bread wheat through Quantitative Trait Loci (QTLs) analysis. Two cultivated bread wheat accessions were selected as parental lines. Population phenotyping was carried out on 133 F_2:3 families. Two field experiments and two experiments in the greenhouse were conducted at IPK-Gatersleben, Germany with control and post-anthesis stress conditions in each experiment. Thousand-grain weight was recorded as the main wheat yield component, which is reduced by post-anthesis drought stress. Chemical desiccation was applied in three experiments as simulator of post-anthesis drought stress whereas water stress was applied in one greenhouse experiment. Analysis of variance showed significant differences among the F_2:3 families. The molecular genetic linkage map including 293 marker loci associated to 19 wheat chromosomes was applied for QTL analysis. The present study revealed four and six QTLs for thousand-grain weight under control and stress conditions, respectively. Only one QTL on chromosome 4BL was common for both conditions. Five QTLs on chromosomes 1AL, 4AL, 7AS, and 7DS were found to be specific to the stress condition. Both parents contributed alleles for drought tolerance. Taking the known reciprocal translocation of chromosomes 4AL/7BS into account, the importance of the short arms of homoeologous group 7 is confirmed for drought stress.     

QTL mapping for developmental behavior of plant height in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

A recombinant inbred line (RIL) population with 305 lines derived from a cross of Hanxuan 10 × Lumai 14 was used to identify the dynamic quantitative trait loci (QTL) for plant height (PH) in wheat (Triticum aestivum L.). Plant heights of RILs were measured at five stages in three environments. Total of seven genomic regions covering PH QTL clusters on different chromosomes identified from a DH population derived from the same cross as the RIL were used as the candidate QTLs and extensively analyzed. Five additive QTLs and eight pairs of epistatic QTLs significantly affecting plant height development were detected by unconditional QTL mapping method. Six additive QTLs and four pairs of epistatic QTLs were identified using conditional mapping approach. Among them, three additive QTLs (QPh.cgb-1B.3, QPh.cgb-4D.1, QPh.cgb-5B.2) and three pairs of epistatic QTLs (QPh.cgb-1B.1–QPh.cgb-1B.3, QPh.cgb-2A.1–QPh.cgb-2D.1, QPh.cgb-2D.1–QPh.cgb-5B.2) were common QTLs detected by both methods. Three QTLs (QPh.cgb-4D.1, QPh.cgb-5B.3, QPh.cgb-5B.4) were expressed under both drought and well-water conditions. The present data are useful for wheat genetic manipulations through molecular marker-assisted selection (MAS), and provides new insights into understanding the genetic mechanism and regulation network underlying the development of plant height in crops. Our result in this study indicated that combining unconditional and conditional mapping methods could make it possible to reveal not only the stable/conserved QTLs for the developmental traits such as plant height but also the dynamic expression feature of the QTLs.     

Genetic effects of introgression genomic components from Sea Island cotton (<Emphasis Type="Italic">Gossypium barbadense</Emphasis> L.) on fiber related traits in upland cotton (<Emphasis Type="Italic">G</Emphasis>. <Emphasis Type="Italic">hirsutum</Emphasis> L.)

The germplasm with exotic genomic components especially from Sea Island cotton (Gossypium barbadense L. Gb) is the dominant genetic resources to enhance fiber quality of upland cotton (G. hirsutum L., Gh). Due to low efficiency of phenotypic evaluation and selection on fiber quality, genetic dissection of favorable alleles using molecular markers is essential. Genetic dissection on putative Gb introgressions related to fiber traits were conducted by SSR markers with mapping populations derived from a cross between Luyuan343 (LY343), a superior fiber quality introgression line (IL) with genomic components from Gb, and an elite Upland cotton cv. Lumianyan#22 (LMY22). Among 82 polymorphic loci screened out from 4050 SSRs, 42 were identified as putative introgression alleles. A total of 29 fiber-related QTLs (23 for fiber quality and six for lint percentage) were detected and most of which clustered on the putative Gb introgression chromosomal segments of Chr.2, Chr.16, Chr.23 and Chr.25. As expected, a majority of favorable alleles of fiber quality QTLs (12/17, not considering the QTLs for fiber fineness) came from the IL parent and most of which (11/12) were conferred by the introgression genomic components while three of the six (3/6) favorable alleles for lint percentage came from the Gh parent. Validation of these QTLs using an F₈ breeding population from the same cross made previously indicated that 13 out of 29 QTLs showed considerable stability. The results suggest that fiber quality improvement using the introgression components could be facilitated by marker-assisted selection in cotton breeding program.     

Molecular characterization of <Emphasis Type="Italic">Fusarium</Emphasis> head blight resistance from wheat variety Wangshuibai

Fusarium head blight (FHB) is a destructive disease of wheat worldwide. FHB resistance genes from Sumai 3 and its derivatives such as Ning 7840 have been well characterized through molecular mapping. In this study, resistance genes in Wangshuibai, a Chinese landrace with high and stable FHB resistance, were analyzed through molecular mapping. A population of 104 F₂-derived F₇ recombinant inbred lines (RILs) was developed from the cross between resistant landrace Wangshuibai and susceptible variety Alondras. A total of 32 informative amplified fragment length polymorphism (AFLP) primer pairs (EcoRI/MseI) amplified 410 AFLP markers segregating among the RILs. Among them, 250 markers were mapped in 23 linkage groups covering a genetic distance of 2,430 cM. In addition, 90 simple sequence repeat (SSR) markers were integrated into the AFLP map. Fifteen markers associated with three quantitative trait loci (QTL) for FHB resistance (P < 0.01) were located on two chromosomes. One QTL was mapped on 1B and two others were mapped on 3B. One QTL on 3BS showed a major effect and explained up to 23.8% of the phenotypic variation for type II FHB resistance.     

Genetic analysis reveals a dominant <Emphasis Type="Italic">S</Emphasis> locus and an <Emphasis Type="Italic">S</Emphasis> suppressor locus in natural self-compatible <Emphasis Type="Italic">Brassica napus</Emphasis>

A self-incompatible (SI) line, S-1300, and its maintainer 97-wen135, a self-compatible (SC) line, were used to study the inheritance of maintenance for self-incompatibility in B. napus. The ratio of SI plants to SC plants from S-1300 × 97-wen135 F₂ and (S-1300 × 97-wen135) × 97-wen135 was 346:260 and 249:232, fitting the expected ratio of 9:7 and 1:1, respectively. Based on these observations, here we propose a genetic model in which two independent loci, S locus and S suppressor locus (sp), are predicted to control the inheritance of maintenance for self-incompatibility in B. napus. The genotypes of S-1300 and 97-wen135 are S ₁₃₀₀ S ₁₃₀₀ sp ₁₃₀₀ sp ₁₃₀₀ and S ₁₃₅ S ₁₃₅ sp ₁₃₅ sp ₁₃₅ , respectively. S ₁₃₅ is dominant to S ₁₃₀₀ , but coexistence of sp ₁₃₀₀ and sp ₁₃₅ fails to suppress S locus. Both S ₁₃₀₀ and S ₁₃₅ can be suppressed by sp ₁₃₅ , while sp ₁₃₀₀ can suppress S ₁₃₅ but not S ₁₃₀₀ . The model contains two characteristics: that a dominant S locus exists in self-compatible B. napus, and that co-suppression will occur when sp loci are heterozygous. The model has been validated by the segregation of S phenotypes in the (S-1300 × 97-wen135) × S-1300, the progenies of SC S-1300 × 97-wen135 F₂ plants and DH population developed from S-1300 × 97-wen135 F₁. This is the first study to report co-suppression of S suppressor loci in B. napus. The genetic model will be very useful for developing molecular markers linked to maintenance for self-incompatibility and for dissecting the mechanism of SI/SC in B. napus.