The influence of a spring habit gene, Vrn-D1, on heading time in wheat

The adaptability of wheat cultivars to environmental conditions is known to be associated with a vernalization requirement, that is, spring/winter habit. To clarify the genetic effect of the spring habit gene, Vrn‐D1, on heading time in the field, recombinant inbred lines (RILs) with or without the Vrn‐D1 gene were produced from F₂ plants of the cross between ‘Nanbukomugi’ and ‘Nishikazekomugi’, non‐carrier and carrier cultivars of this gene, respectively. Using growth chambers with a controlled temperature and photoperiod, three components of heading time, i.e. vernalization requirement, photoperiodic sensitivity and narrow‐sense earliness (earliness per se), were evaluated in each RIL. RILs with the Vrn‐D1 gene (E lines) showed greatly reduced vernalization requirements and slightly shorter narrow‐sense earliness than RILs without Vrn‐D1 (L lines), although no difference in photoperiodic sensitivity was observed between the two groups. RILs were planted at four different sites in Japan and examined for their heading time in the field. E lines headed significantly earlier than L lines at all locations, indicating that the earliness of E lines is stable in various environmental conditions. These results indicated that spring habit caused by Vrn‐D1 gene, as well as narrow‐sense earliness, was responsible for heading time in the field.     

Genetic Control of Vernalization, Day-length Response, and Earliness per se by Homoeologous Group-3 Chromosomes in Wheat

To identify homoeologous group-3 chromosomes that carry genes for vernalization, day-length responses, and earliness per se, a series of aneuploid lines (mono-somics and tetrasomics) and chromosome-substitution lines in ‘Chinese Spring’ (CS) were surveyed under different vernalization and day-length regimes in controlled environments. The results indicated that genes on all three chromosomes of group 3 can have striking effects on ear-emergence time. The replacement of CS 3B by its homologues in ‘Lutescens 62’ and ‘Cheyenne’ produced an increased insensitivity to vernalization, while 3B homologues from ‘Ceska Presivka’ gave CS a remarkable sensitivity to vernalization. This provided evidence for multiple allelism at a new Vrn locus on chromosome 3B. A negative association between gene dosage and day-length response was found in CS 3D which was thought to carry a gene for promoting insensitivity to day-length. The behaviour of CS monosomic 3A and CS (Timstein 3A), in reducing numbers of days to heading independently of environmental stimuli, suggested the presence of earliness per se genes on this chromosome.     

Chromosomal locations and genetic relationships of tiller and spike characters in wheat

Number of tillers per plant, plant growth habit in seedling and adult stages, and spike and spikelet characters are agronomically important features of the gross morphology of wheat. To localize to wheat chromosomes the genes for these traits, we scored them in a set of wheat recombinant-inbred mapping lines already well genotyped with molecular markers. Quantitative-trait analysis revealed a region near Gli-A2 (Xpsr10) on the short arm of chromosome 6A strongly affecting tiller number and the correlated trait of seedling growth habit. Genes with opposing effects on adult plant type were localized on the short arms of chromosomes2A and 3A, while genes affecting spike development were assigned to several A- and B-genome chromosomes. None of these genes showed synteny with counterpart QTLs reported to affect the same traits in rice. In the chromosome 2D region containing the photoperiod-insensitivity gene Ppd-D1, the major determinant of heading date in these autumn-sown lines, earliness alleles reduced tiller and spikelet numbers and increased erect seedling growth habit, but showed no influence on adult plant type or spike length. Though several of these morphological traits are generally considered to be associated with winter hardiness and their phenotypic intercorrelations were consistent with the genetic mapping evidence, no association was found between newly identified loci and known vernalization-response or frost-resistance loci. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of barley chromosome on heading characters in wheat-barley chromosome addition lines

Heading time in cereals is a composite character determined by vernalization requirement, photoperiodic sensitivity and narrow-sense earliness. To study the effects of added barley chromosomes on the heading characters in wheat, two sets of wheat-barley chromosome addition lines, i.e., ‘Betzes’ barley chromosomes 2H to 7H added to ’Chinese Spring‘ wheat (CS-Be2H to CS-Be7H) and ‘New Golden’ barley chromosomes 5H and 6H added to ‘Shinchunaga’ wheat (Shi-NG5H, Shi-NG6H), were examined for their heading characters. All barley chromosomes except Be6H affected vernalization requirement and/or narrow-sense earliness in CS or Shi. Be5H chromosome also slightly increased the photoperiodic sensitivity of CS. Shi-NG5H addition line showed significantly decreased vernalization requirement in comparison with Shi, whereas CS-Be5H did not show any difference from CS. The F₁ hybrid of the cross, Shi-NG5H × CS-Be5H, exhibited the same level of vernalization insensitivity as the Shi-NG5H addition line, and plants with and without a vernalization requirement segregated in a 1 : 3 ratio in the F₂ generation. These observations, together with previous reports, suggest that the decreased vernalization requirement in the Shi-NG5H addition line was caused by the presence of a major dominant gene for spring habit, Sh₂, located on the NG5H barley chromosome. Furthermore, this study revealed that the Sh₂ gene in barley has a similar but weaker effect than the wheat vernalization insensitive gene, Vrn1, on the vernalization response in wheat. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of QEet.ocs-5A.1, a quantitative trait locus for ear emergence time on wheat chromosome 5AL

QEet.ocs‐5A.1, a quantitative trait locus controlling ear emergence time, has been detected on wheat chromosome 5AL using single chromosome recombinant lines (SCRs) developed from a cross between ‘Chinese Spring’ (CS) (‘Cappelle‐Desprez’ 5A) and CS (Triticum spelta 5A). This locus has little influence on grain yield and its components, and thus has breeding potential for changing ear emergence time without yield reduction. To characterize the phenotypic expression of QEet.ocs.1 and to test its interaction with the Vrn‐A1 gene for vernalization response, six near‐isogenic SCRs differing for these two gene regions were grown together with the parental controls under different vernalization and photoperiod regimes. The T. spelta allele of QEet.ocs.1 accelerated heading time when vernalization and photoperiod were satisfied, demonstrating that the function of this QTL is earliness per se. There was no interaction between Vrn‐A1 and QEet.ocs.1.     

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.     

Relationship between molecular marker heterozygosity and hybrid performance in intra- and inter-subspecific crosses of rice

The objective of this study was to investigate the relationship between molecular marker diversity and heterosis in both intra-and inter-sub-specific hybrids of rice to evaluate the feasibility of predicting hybrid performance using molecular markers. Eleven elite lines were intermated resulting in a diallel set including 10 indica × indica, 15 japonica × japonica and 30 indica × japonica crosses. The F₁ hybrids and parents were evaluated for agronomic performance in a replicated field trial. The parental lines were tested for DNA polymorphisms with 113 restriction fragment length polymorphism (RFLP) probes covering the 12 rice chromosomes. Inter-subspecific crosses showed better performance and higher heterosis than intrasubspecific hybrids. Correlations of marker heterozygosity with hybrid performance and heterosis differed considerably between the two subspecies; they were higher in crosses within japonica subspecies than within indica subspecies. Very little correlation was detected in intersubspecific crosses. It was concluded that relationships between marker heterozygosity and hybrid performance were complex owing to germplasm diversity and the complexity of the genetic basis of heterosis. The implications of the results in predicting hybrid performance using molecular markers are discussed.     

QTL analysis for grain weight in common wheat

Quantitative trait loci (QTL) analysis for grain weight (GW = 1000 grain weight) in common wheat was conducted using a set of 100 recombinant inbred lines (RILs) derived from a cross ‘Rye Selection 111 (high GW) × Chinese Spring (low GW)’. The RILs and their two parental genotypes were evaluated for GW in six different environments (three locations × two years). Genotyping of RILs was carried out using 449 (30 SSRs, 299 AFLP and 120 SAMPL) polymorphic markers. Using the genotyping data of RILs, framework linkage maps were prepared for three chromosomes (1A, 2B, 7A), which were earlier identified by us to carry important/major genes for GW following monosomic analysis. QTL analysis for GW was conducted following genome-wide single marker regression analysis (SMA) and composite interval mapping (CIM) using molecular maps for the three chromosomes. Following SMA, 12 markers showed associations with GW, individual markers explaining 6.57% to 10.76% PV (phenotypic variation) for GW in individual environments. The high grain weight parent, Rye Selection111, which is an agronomically superior genotype, contributed favourable alleles for GW at six of the 12 marker loci identified through SMA. The CIM identified two stable and definitive QTLs, one each on chromosome arms 2BS and 7AS, which were also identified through SMA, and a third suggestive QTL on 1AS. These QTLs explained 9.06% to 19.85% PV for GW in different environments. The QTL for GW on 7AS is co-located with a QTL for heading date suggesting the occurrence of a QTL having a positive pleiotropic effect on the two traits. Some of the markers identified during the present study may prove useful for marker-assisted selection, while breeding for high GW in common wheat.     

Molecular and comparative mapping for heading date and plant height in oat

Selection of oat genotypes combining earliness and short plant height could stimulate oat cultivation worldwide. However, the mechanisms involved with the genetic control of heading date and plant height traits are not fully understood to date. This study aimed to identify genomic regions controlling heading date and plant height in two hulled by naked oat populations and to compare these genomic regions with that of other grass species. Recombinant inbred lines of each population and their parents were genotyped by a 6 K BeadChip Illumina Infinium array and assessed for heading date and plant height in two sowing dates. The quantitative trait loci (QTL) affecting these traits were detected by simple interval mapping. The two oat populations showed different genetic mechanisms controlling heading date. A major QTL was identified in one of the populations, mapped into the ‘Mrg33’ consensus linkage group from the current oat map. Two other QTL were detected into the ‘Mrg02’ and ‘Mrg24’ groups, in the second population. On the other hand, both populations presented the same genomic region controlling plant height. Six SNP markers, mapping on the same linkage group within each population, were associated with the trait, regardless the sowing date, explaining more than 20% of the phenotypic variation. Five of these six markers were mapped into three different linkage groups on the oat consensus map. Genomic regions associated with heading date and plant height in oat seem to be conserved in Oryza sativa L. and Brachypodium distachyon. Our results provide valuable information for marker-assisted selection in oats, allowing selection for earliness and plant height on early segregating generations.     

A QTL for early heading in wheat cultivar Suwon 92

Heading date is an important trait that determines wheat adaptation to environments. A recombinant inbred line (RIL) population derived from CI 13227 × Suwon 92 was employed to tag the quantitative trait locus (QTL) for early heading in Suwon 92. This population was phenotyped for heading date in 1994, 1995, and 1997, and analyzed with AFLP and SSR markers. Two AFLP markers (XGCTG.CGCT118 and XGCTG.CGCT60) closely associated with heading date were identified. Across years, XGCTG.CGCT118 and XGCTG.CGCT60 explained 40.4% and 32.2% of the total phenotypic variances, respectively. Interval analysis revealed a major QTL for heading date, designated QHd.pser-2DS, between AFLP marker XGCTG.CGCT118 and SSR marker Xgwm261. Based on the linkage map, QHd.pser-2DS was about 41.2 cM proximal to the distal end of chromosome 2DS, and explained 40.5% of the phenotypic variance across three years. The identified markers associated with the early heading QTL have the potential to be used in wheat breeding programs.     

Development and characterization of common wheat-Thinopyrum intermedium translocation lines with resistance to barley yellow dwarf virus

We developed some wheat-Th. intermedium translocation lines,Yw642, Yw443 and Yw243, etc., showing good BYDV resistance from L1by induced homoeologous pairing using CS ph mutant. Characterization ofthese wheat lines was carried out by GISH and RFLP analysis. The resultsof GISH showed that the lines, YWw42, Yw443 and Yw243, etc., arehomozygous wheat-Th. intermedium translocation lines, in which thechromosome segments of Th. intermedium were transferred to thedistal end of a pair of wheat chromosomes. RFLP analysis indicated that thetranslocation chromosome of the wheat lines is T7DS · 7DL-7XL. Thebreakpoint of the translocation is located on the distal end of 7DL, betweenXpsr965 and Xpsr680 about 90–99 cm from the centromere. The BYDVgene is located on the distal end of 7XL around Xpsr680, Xpsr687 andXwg380. The RFLP markers of psr680, psr687 and wg380 werecosegregated with the BYDV resistance respectively and could be used formolecular assisted selection (MAS) in wheat breeding program for BYDVresistance.     

Genes for frost resistance in wheat

Wheat varieties differ in their responses to low temperatures. Geneticstudies on frost resistance in wheat are difficult because the effects arequantitative in nature and thus require precise genetic material andreproducible experimental conditions. The detailed diallel analyses indicatedthat the inheritance of frost resistance is polygenic and mostly additive.Nevertheless, studies using monosomic, ditelosomic and substitution lineshave identified specific chromosomes that carry genes responsible for frostresistance. In particular, the chromosomes 5A and 5D appear to carrymajor genes. Using molecular markers (RFLP, AFLP) and recombinantsubstitution lines it was shown that the Vrn-A1 (vernalization) and Fr1 (frost resistance) loci were located closely linked on the distal portionof the long arm of 5A, but recombination between them was found (cM = 2). The RFLP markers Xpsr426 and Xwg644 were tightlylinked to the Vrn-A1 locus. Loci Vrn-D1 and Fr2are located on the long arm of 5D. Fr2 and Vrn-D1 arehomoeologous to Fr1 and Vrn-A1. A physical map of theVrn-A1 and Fr1 genes was constructed on chromosome 5Ausing deletion lines. This cytogenetically based physical map could be usefulin further work on genome mapping and gene cloning.     

Genome-wide association study of differences in 14 agronomic traits under low- and high-density planting models based on the 660k SNP array for common wheat

One hundred and ninety-seven wheat accessions from Yellow and Huai Winter Wheat Region (YHW) were evaluated for differences of 14 agronomic traits under low- and high-density plantings. Compared with the high-density plantings, plant height, neck length, uppermost internode length, flag leaf angle and number of sterile spikelets under the low-density plantings reduced, while heading date, flowering date, flag leaf length and width, spike length, number of fertile spikelets, grain number per spike, thousand-kernel weight and grain weight per spike increased. A total of 1,118 markers were detected based on GWAS, and seven QTLs were confirmed. One QTL on chromosomes 5BL and two other QTLs on 5Dl were all tightly associated with flowering date difference. Bioinformatics analysis revealed that two haploblocks in 5Dl were involved, and the Vrn-D1 locus was located in this interval. A region on chromosome 5B at around 531.5 Mb was significantly associated with plant height difference. Two QTLs including AX-94840438 (7BL) and AX-94563647 (7DS) were responsible for neck length or uppermost internode length difference.     

Molecular mapping of S-c, an F1 pollen sterility gene in cultivated rice

Hybrids between indica and japonica rice varieties usually show partial sterility, and are a major limiting factor in the utilization of heterosis at subspecific level. When studying male-gamete (pollen) abortion, a possibly important cause for sterility, six loci (S-a, S-b, S-c, S-d, S-e and S-f) for F₁ pollen sterility were identified. Here we report genetic and linkage analysis of S-c locus using molecular markers in a cross between Taichung 65, a japonica variety carrying allele S-c ^j, and its isogenic line TISL5, carrying alleleS-c ^j. Our results show that pollen sterility occurring in the hybrids is controlled by one locus. We used 208 RFLP markers, as well as 500 RAPD primers, to survey the polymorphism between Taichung 65 and TISL5. Six RFLP markers located on a small region of chromosome 3, detected different RFLP patterns. Co-segregation analysis of fertility and RFLP patterns with 123 F₂ plants confirmed that the markers RG227, RG391, R1420 were completely linked with the S-c locus. The genetic distances between the markers C730, RG166 and RG369 and the S-c locus were 0.5 cM, 3.4 cM, and 3.4 cM respectively. Distorted F₂ ratios were also observed for these 4 RFLP markers in the cross. This result suggests that the `one locus sporo-gametophytic' model could explain F₁ hybrid pollen sterility in cultivated rice. RG227, the completely linked marker, has been converted to STS marker for marker-assisted selection. This revised version was published online in August 2006 with corrections to the Cover Date.     

杂交水稻恢复系桂99的抽穗期基因及其效应分析

以基因型明确的抽穗期主基因近等基因系EG0~EG7、ER~LR、T65系列为测验系（TLs）,在江西南昌（28^o 36’ N）夏季自然高温长日（14 h/d）和人工遮光短日（10 h/d）,以及海南三亚（18^o 14’ N）旱季自然低温短日（11.6 h/d）处理条件下,对籼型杂交水稻恢复系桂99的抽穗期基因及其感温性和基因位点间的互作效应进行了分析。结果表明,桂99在E₁、E₂和E₃位点分别带有感光迟熟等位基因E₁、E₂和E₃,在Se-1位点带有非感光等位基因Se-1^e,在Ef-1位点带有早熟基因Ef-1,由此推断其抽穗期基因型为E₁E₁E₂E₂E₃E₃Se-1^eSe-1^eEf-1Ef-1。迟熟基因E₁、E₃与早熟基因Ef-1同时存在,E₁、E₃与Se-1^e基因位点间的互作使桂99农艺性状表现弱感光性。感光基因Se-1^u（或Se-1ⁿ）的存在能增强E位点感光迟熟基因的感光性,感光基因对“TLs×桂99”F₂植株抽穗的影响,是延长平均抽穗期,增加迟抽穗植株分布频率。分析了感温性对TLs抽穗期的影响,讨论了以桂99为恢复系配置的杂交水稻组合丰产性和广适性的遗传基础。     

Construction and evaluation of introgression lines and fine mapping of ehd8 from Jinghong common wild rice (Oryza rufipogon)

Heading date is one of the most important traits in rice and regulated by multiple genes. Common wild rice is the ancestor of Asian cultivated rice and harbours abundant genetic diversity. To use wild rice resource in rice breeding, a set of 154 introgression lines (ILs) covering 93% of the genome of Jinghong common wild rice was constructed in the background 'Teqing', using 208 simple sequence repeat markers evenly distributed on 12 chromosomes. Among the ILs, the line JIL64 displayed late heading independent of photoperiod. Genetic analysis using the two F₂ populations crossed ''Teqing'/JIL64 and JIL64/'Teqing' revealed that late flowering was controlled by a recessive gene on chromosome 8 (designated early heading date 8, ehd8), and ehd8 was fine mapped to the 50‐kb region flanked by markers RM22221 and 64Indel4. Sequencing and qRT‐PCR demonstrated that LOC_Os08g01410 and LOC_Os08g01420 were deleted in JIL64 and may be associated with the late heading of Jinghong common wild rice. These findings lay a practical foundation for characterizing ehd8, and the ILs help to mine genes from Jinghong common wild rice.     

Molecular characterization of the recombinant inbred line population derived from a japonica-indica rice cross

Recombinant inbred line (RIL) populations of rice are useful genetic sources for map-based cloning of agronomically important genes. Zhe733 is a high-yielding indica cultivar from China conferring resistance to rice blast (RB), rice water weevil (RWW) and straighthead; whereas Kaybonnet low-phytic acid 1-1 (KBNTlpa) is a mutant of a tropical japonica cultivar from the US containing low-phytic acid with average yield, and is susceptible to some RB races, RWW, and straighthead. A 355 RIL F₁₀₋₁₁ population derived from the cross of KBNTlpa × Zhe733 was recently released. Simple sequence repeat (SSR) markers were used to evaluate 269 RILs of this population. A total of 107 polymorphic markers were mapped on all rice chromosomes representing a total of 1,016.3 cM of genetic distance. Two hundred and thirty-five KBNTlpa × Zhe733 RILs (KZRILs) were clustered into seven groups based on allele frequencies of SSR markers. Twenty-three markers (21.1%) on chromosomes 3, 6, 7, 9, and 11 were found to favor Zhe733 (χ ² = 16.8−189.7 and P < 0.01) and five markers (4.6%) on chromosome 1 and 6 were found to favor KBNTlpa (χ ² = 18.5−46.6 and P < 0.01). Marker segregations were observed to be normal for both parents except 26 (10.2%) KZRILs were found to skew toward Zhe733 (χ ² > 15.7 and P < 0.01). Furthermore, the average frequencies of heterozygosity and non-parental alleles per KZRIL were 1.3% (0.0−38.9%) and 0.4% (0.0−15.0%), respectively. Thirteen heterozygous KZRILs were found at more than five markers loci and nine KZRILs were found with more than five non-parental alleles representing 5.1 and 3.5% of 255 KZRILs. Overall, this KZRIL population is a good population with relatively low frequencies of heterozygosity and non-parental alleles, and with relatively low percentages of skewed markers and skewed KZRILs. The profiles of these SSR markers should facilitate molecular tagging critical genes controlling yield, RB, RWW, and straighthead resistance.     

玉米简单重复序列不对等交换的热点区域定位

生物基因组中简单重复序列的多态性是同源染色体不对等交换的结果之一,因此明确不对等交换的热点区域具有重要的理论意义。利用来源于优良玉米杂交种豫玉22的一套重组近交系(RIL)群体,对其遗传组成进行了SSR标记分析,发现40个不对等交换的SSR标记,不对等交换在群体间发生的概率介于0.34%~14.63%之间,每世代发生的频率为10^-2~10^-1,其中(AG)n重复的标记占发生不对等交换总标记的58.3%。有31个不对等交换标记分布于染色体上的11个热点区域,位于第9染色体以外的其它染色体上,其中第3和第5染色体上各分布2个不对等交换的热点区域。     

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.     

The use of bulked segregant analysis to accumulate RAPD markers near a locus for beet cyst nematode resistance in Beta vulgaris

Bulked segregant analysis (BSA) was used to accumulate RAPD markers near the beet cyst nematode resistance locus Hsl^pro-1 of sugar beet (Beta vulgaris L.). Graphical genotypes constructed from RFLP data were utilized to select F₂ individuals in (1) the construction of pools of plants used in the initial screening for polymorphisms, and (2) the selection of individual plants used to confirm the potential linkage. The pooled DNA samples were screened for polymorphisms using 668 RAPD primers. Forty-four candidate markers potentially linked to the region were analysed further using 14 segregating individuals. Close linkage was confirmed for 17 of the markers. Four of the RAPD markers were assigned map coordinates within the RFLP map. Three of these markers extended the RFLP map by 3cM. Altogether, the 8cM target interval contains 10 RFLP and 17 RAPD markers, corresponding to an average marker density of 0.3cM in the Hsl_pro-1 region.