Quantitative trait loci for temperature-sensitive resistance to <Emphasis Type="Italic">Puccinia striiformis</Emphasis> f. sp. <Emphasis Type="Italic">tritici</Emphasis> in wheat cultivar Flinor

Stripe (yellow) rust, caused by Puccinia striiformis Westend. f. sp. tritici Eriks. (Pst), is an important disease of wheat (Triticum aestivum L.) globally. Use of host resistance is an important strategy to manage the disease. The cultivar Flinor has temperature-sensitive resistance to stripe rust. To map quantitative trait loci (QTLs) for these temperature-sensitive resistances, Flinor was crossed with susceptible cultivar Ming Xian 169. The seedlings of the parents, and F₁, F₃ progeny were screened against Chinese yellow rust race CYR32 in controlled-temperature growth chambers under different temperature regimes. Genetic analysis confirmed two genes for temperature-sensitive stripe rust resistance. A linkage map of SSR markers was constructed using 130 F₃ families derived from the cross. Two temperature-sensitive resistance QTLs were detected on chromosome 5B, designated QYr-tem-5B.1 and QYr-tem-5B.2, respectively, and are separated by a genetic distance of over 50 cM. The loci contributed 33.12 and 37.33% of the total phenotypic variation for infection type, respectively, and up to 70.45% collectively. Favorable alleles of these two QTLs came from Flinor. These two QTLs are temperature-sensitive resistance loci and different from previously reported QTLs for resistance to stripe rust.     

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.     

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.     

Legume breeding for rust resistance: lessons to learn from the model <Emphasis Type="Italic">Medicago truncatula</Emphasis>

Rusts are major biotic constraints of legumes worldwide. Breeding for rust resistance is regarded as the most cost efficient method for rust control. However, in contrast to common bean for which complete monogenic resistance exists and is efficiently used, most of the rust resistance reactions described so far in cool season food legumes are incomplete and of complex inheritance. Incomplete resistance has been described in faba bean, pea, chickpea and lentil and several of their associated QTLs have been mapped. However, the relatively large distance between the QTLs and their associated molecular markers hampers their efficient use for marker assisted selection. Their large genome size drastically hampers the development of genomic resource and limits the saturation of their genetic maps. The use of model plants such as the model legume Medicago truncatula may circumvent this drawback. The important genetic and genomic resources and tools available for this model legume can considerably speed up the discovery and validation of new genes and QTLs in resistance to legume pathogens. Here, the potential of M. truncatula as a model to study rust resistance in legumes, and to transfer rust resistance genes to cool season grain legumes is reviewed.     

QTL mapping and identification of corresponding genomic regions for black pod disease resistance to three <Emphasis Type="Italic">Phytophthora</Emphasis> species in <Emphasis Type="Italic">Theobroma cacao</Emphasis> L.

The cacao tree (Theobroma cacao L.) is a species of great importance because cacao beans are the raw material used in the production of chocolate. However, the economic success of cacao is largely limited by important diseases such as black pod, which is responsible for losses of up to 30–40% of the global cacao harvest. The discovery of resistance genes could extensively reduce these losses. Therefore, the aims of this study were to construct an integrated multipoint genetic map, align polymorphisms against the available cacao genome, and identify quantitative trait loci (QTLs) associated with resistance to black pod disease in cacao. The genetic map had a total length of 956.41 cM and included 186 simple sequence repeat (SSR) markers distributed among 10 linkage groups. The physical “in silico” map covered more than 200 Mb of the cacao genome. Based on the mixed model predicted means of Phytophthora evaluation, a total of 6 QTLs were detected for Phytophthora palmivora (1 QTL), Phytophthora citrophthora (1 QTL), and Phytophthora capsici (4 QTLs). Approximately 1.77–3.29% of the phenotypic variation could be explained by the mapped QTLs. Several SSR marker-flanking regions containing mapped QTLs were located in proximity to disease regions. The greatest number of resistance genes was detected in linkage group 6, which provides strong evidence for a QTL. This joint analysis involving multipoint and mixed-model approaches may provide a potentially promising technique for detecting genes resistant to black pod and could be very useful for future studies in cacao breeding.     

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.     

Molecular genetic analysis of flour color using a doubled haploid population in bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Flour color is an important trait in the assessment of flour quality for the production of many end products. In this study, quantitative trait loci (QTLs) with additive effects, epistatic effects, and QTL × environment (QE) interactions for flour color in bread wheat (Triticum aestivum L.) were studied, using a set of 168 doubled haploid (DH) lines derived from a Huapei 3 × Yumai 57 cross. A genetic map was constructed using 283 simple sequence repeats (SSR) and 22 expressed sequence tags (EST)-SSR markers. The DH and parents were evaluated for flour color in three environments. QTL analyses were performed using QTLNetwork 2.0 software based on a mixed linear model approach. A total of 18 additive QTLs and 24 pairs of epistatic QTLs were detected for flour color, which were distributed on 19 of the 21 chromosomes. One major QTL, qa1B, closely linked to barc372 0.1 cM, could account for 25.64% of the phenotypic variation of a* without any influence from the environments. So qa1B could be used in the molecular marker-assisted selection (MAS) in wheat breeding programs. The results showed that both additive and epistatic effects were important genetic basis for flour color, and were also sometimes subject to environmental modifications. The information obtained in this study should be useful for manipulating the QTLs for flour color by MAS in wheat breeding programs. Kun-Pu Zhang and Guang-Feng Chen contributed equally to this study.     

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.     

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.     

Identification of microsatellite markers linked to the blast resistance gene <Emphasis Type="Italic">Pi-1(t)</Emphasis> in rice

The present work was conducted to identify microsatellite markers linked to the rice blast resistance gene Pi-1(t) for a marker-assisted selection program. Twenty-four primer pairs corresponding to 19 microsatellite loci were selected from the Gramene database (www. gramene.org) considering their relative proximity to Pi-1(t) gene in the current rice genetic map. Progenitors and DNA bulks of resistant and susceptible families from F₃ segregating populations of a cross between the near-isogenic lines C101LAC (resistant) and C101A51 (susceptible) were used to identify polymorphic microsatellite markers associated to this gene through bulked segregant analysis. Putative molecular markers linked to the blast resistance gene Pi-1(t) were then used on the whole progeny for linkage analysis. Additionally, the diagnostic potential of the microsatellite markers associated to the resistance gene was also evaluated on 17 rice varieties planted in Latin America by amplification of the specific resistant alleles for the gene in each genotype. Comparing with greenhouse phenotypic evaluations for blast resistance, the usefulness of the highly linked microsatellite markers to identify resistant rice genotypes was evaluated. As expected, the phenotypic segregation in the F₃ generation agreed to the expected segregation ratio for a single gene model. Of the 24 microsatellite sequences tested, six resulted polymorphic and linked to the gene. Two markers (RM1233*I and RM224) mapped in the same position (0.0 cM) with the Pi-1(t) gene. Other three markers corresponding to the same genetic locus were located at 18.5 cM above the resistance gene, while another marker was positioned at 23.8 cM below the gene. Microsatellite analysis on elite rice varieties with different genetic background showed that all known sources of blast resistance included in this study carry the specific Pi-1(t) allele. Results are discussed considering the potential utility of the microsatellite markers found, for MAS in rice breeding programs aiming at developing rice varieties with durable blast resistance based on a combination of resistance genes. Centro Internactional de Agricultura Tropical (CIAT) institute where the research was carried out     

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.     

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.     

Mapping quantitative trait loci conferring blast resistance in upland indica rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

A genetic analysis of blast resistance in upland rice variety is very crucial. In this study, we performed a linkage mapping of quantitative trait loci (QTLs) for blast resistance using an advanced backcross population from a cross between Way Rarem (susceptible indica variety) and Oryzica Llanos 5 (durable resistant indica variety). A transgressive segregation was observed in the advanced backcross population of Way Rarem//Oryzica Llanos 5. A total of 16 QTLs have been identified along chromosomes 1, 3, 5, 6, 7, 8, 9, and 11 against eight blast pathogen isolates. Each QTL accounted from 11.31 to 45.11% of the variation in blast resistance. Most QTLs showed race specificity, demonstrating the small effect of such QTLs. Unexpectedly, several superior blast resistance alleles were contributed by Way Rarem, the susceptible-recurrent parent. Among eight candidate defense response genes detected in several loci, a single gene (oxalate oxidase) present on chromosome 3 was found to be associated with blast resistance in upland indica rice. Ultimately, these advanced backcross lines with resistance to blast tagged by markers might be useful for pyramiding blast resistance alleles in upland rice.     

An intraspecific genetic map of water yam (<Emphasis Type="Italic">Dioscorea alata</Emphasis> L.) based on AFLP markers and QTL analysis for anthracnose resistance

Water yam (Dioscorea alata L.) is the most widely cultivated food yams. Despite its importance, its production is limited by anthracnose disease caused by Colletotrichum gloeosporioides (Penz.). The use of resistant yam varieties is the most reliable approach of management of this disease. The speed and precision of breeding can be improved by the development of genetic linkage maps which would provide the basis for locating and hence manipulating quantitative traits such as anthracnose resistance in breeding programmes. An F1 diploid population was developed by crossing ‘Boutou’ a female clone (with field resistance to anthracnose) with ‘Pyramide’ (susceptible). A linkage map was generated with 523 polymorphic markers from 26 AFLP primer combinations. The resulting map covered a total length of 1538 cM and included 20 linkage groups. It is the most saturated of all genetic linkage maps of yam to date. QTL analysis of anthracnose resistance was performed based on response to two isolates of C. gloeosporioides. Resistance to anthracnose appeared to be inherited quantitatively. Using a LOD significance threshold of 2.6 we identified a total of nine QTLs for anthracnose resistance. The phenotypic variance explained by each QTL ranged from 7.0 to 32.9% whereas the total amount of phenotypic variation for anthracnose resistance explained by all significant QTLs varied from 26.4 to 73.7% depending on the isolate and the variable considered. These QTLs displayed isolate-specific resistance as well as broad spectrum resistance. The availability of molecular markers linked to the QTLs of anthracnose resistance will facilitate marker-assisted selection in breeding programmes.     

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.     

Fine mapping of <Emphasis Type="Italic">Rf3</Emphasis> and <Emphasis Type="Italic">Rf4</Emphasis> fertility restorer loci of WA-CMS of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) and validation of the developed marker system for identification of restorer lines

The Wild Abortive (WA) system is the major cytoplasmic male sterility (CMS) source for hybrid rice production in indica rice and its fertility restoration is reported to be controlled by two major loci viz. Rf3 on chromosome 1 and Rf4 on chromosome 10. With the availability of the rice genome sequence, an attempt was made to fine map, develop candidate gene based markers for Rf3 and Rf4 and validate the developed marker system in a set of known restorer lines. Using polymorphic markers developed from microsatellite markers and candidate gene based markers from Rf3 and Rf4 loci, local linkage maps were constructed in two mapping populations of ~1,500 F₂ progeny from KRH2 (IR58025A/KMR3R) and DRRH2 (IR68897A/DR714-1-2R) hybrids. QTLs and their interactions for fertility restoration in Rf3 and Rf4 loci were identified. The identified QTL in both mapping populations together explained 66–72 % of the phenotypic variance of the trait suggesting their utility in developing a marker system for identification of fertility restorers for WA-CMS. Sequence comparison of the two candidate genes from the Rf3 and Rf4 regions in male sterile (A) and restorer (R) lines showed 2–3 bp indels and a few substitutions in the Rf3 region and indels of 327 and 106 bp in the Rf4 region respectively. The marker system identified in the present study was validated in 212 restorers and 34 maintainers along with earlier reported markers for fertility restoration of WA-CMS. Together DRCG-RF4-14 and DRCG-RF4-8 for the Rf4 locus and DRRM-RF3-5/DRRM-RF3-10 for the Rf3 locus showed a maximum efficiency of 92 % for identification of restorers.     

Genetic combining ability for concentration of mineral elements in cabbage head (<Emphasis Type="Italic">Brassica oleracea</Emphasis> var<Emphasis Type="Italic">. capitata</Emphasis> L.)

Brassica vegetables are important source of dietary nutrition. However, information on the genetic combining ability of mineral elements such as iron, zinc, copper, manganese, potassium and calcium or their types of genetic effects (i.e. additive or non-additive) is scarce but important as it influences the selection of parents and breeding approaches to be adopted for improvement of nutritional quality of cabbage. Therefore, an attempt was made to estimate combining ability in a line × tester (5 × 11) mating design for minerals. Significant mean square for line × tester interaction was observed for all minerals under study indicating the prevalence of non-additive variance; while less than unity value of σ_gca² /σ_sca² ratio for iron, zinc, manganese, potassium and calcium accumulation indicate predominance of non-additive gene action. The parents 83-2, Pride of Asia, Pusa Mukta, Red Cabbage and MR-1 were found good general combiners for four mineral elements. The general combining ability effects of the parents for various minerals revealed that none of the parents excelled for all the minerals suggesting the need for multiple crossing approaches. The cross 83-1 × AC-1019 (Poor × Poor general combiner) exhibits desirable significant specific combining ability effects for all six minerals might be due to presence of high magnitude of non-additive especially complementary epistatic effects which can be utilize for commercial exploitation of heterosis. This study shows clearly that specific combining ability is more important than general combining ability for predicting hybrid combinations for high mineral content in cabbage head.     

Molecular markers linked to <Emphasis Type="Italic">Bn</Emphasis>;<Emphasis Type="Italic">rf</Emphasis>: a recessive epistatic inhibitor gene of recessive genic male sterility in <Emphasis Type="Italic">Brassica napus </Emphasis>L.

7–7365AB is a recessive genic male sterile (RGMS) two-type line, which can be applied in a three-line system with the interim-maintainer, 7–7365C. Fertility of this system is controlled by two duplicate dominant epistatic genes (Bn;Ms3 and Bn;Ms4) and one recessive epistatic inhibitor gene (Bn;rf). Therefore an individual with the genotype of Bn;ms3ms3ms4ms4Rf_ exhibits male sterility, whereas, plant with Bn;ms3ms3ms4ms4rfrf shows fertility because homozygosity at the Bn;rf locus (Bn;rfrf) can inhibit the expression of two recessive male sterile genes in homozygous Bn;ms3ms3ms4ms4 plant. A cross of 7–7365A (Bn;ms3ms3ms4ms4RfRf) and 7–7365C (Bn;ms3ms3ms4ms4rfrf) can generate a complete male sterile population served as a mother line with restorer in alternative strips for the multiplication of hybrid seeds. In the present study, molecular mapping of the Bn;Rf gene was performed in a BC₁ population from the cross between 7–7365A and 7–7365C. Bulked segregant analysis (BSA) and amplified fragment length polymorphism (AFLP) technique was used to identify molecular markers linked to the gene of interest. From a survey of 768 primer combinations, seven AFLP markers were identified. The closest marker, XM5, was co-segregated with the Bn;Rf locus and successfully converted into a sequence characterized amplified region (SCAR) marker, designated as XSC5. Two flanking markers, XM3 and XM2, were 0.6 cM and 2.6 cM away from the target gene, respectively. XM1 was subsequently mapped on linkage group N7 using a doubled-haploid (DH) mapping population derived from the cross Tapidor × Ningyou7, available at IMSORB, UK. To further confirm the location of the Bn;Rf gene, additional simple sequence repeat (SSR) markers in linkage group N7 from the reference maps were screened in the BC₁ population. Two SSR markers, CB10594 and BRMS018, showed polymorphisms in our mapping population. The molecular markers found in the present study will facilitate the selection of interim-maintainer.     

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.     

A major QTL associated with preharvest sprouting in rapeseed (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

Preharvest sprouting (PHS) is one of the most important factors affecting the cereal production worldwide, in regions characterized by rainfall and high humidity during harvest season. It is sometimes a problem in rapeseed (Brassica napus L.), especially in production of commercial F₁ hybrids. To detect quantitative trait loci (QTL) controlling PHS, a F₂ population consisting of 269 F_2:3 lines was created from the cross between a PHS-tolerant line (117AB) and a PHS-susceptible line (7,605). A linkage map was constructed using 35 Simple Sequence Repeat markers and 242 Amplified Fragment Length Polymorphism markers. PHS was measured as a percentage of sprouted seeds on the mother plant, 7 days after physiological maturity. Five putative QTLs for PHS were detected and located on LG2 (N11) and LG7 (N3), respectively. Phenotypic variance explained by each QTL ranged from 4.11 to 50.78% and the five putative QTLs explained about 75.63% of the total phenotypic variance. A major QTL was identified on LG2 (N11) flanked by P3C4180 and C6C13160, which explained 50.78% of the total phenotypic variance. Meanwhile, we detected four significant epistatic interactions with a total contribution of 17.16% of the total phenotypic variance.