Fine mapping of the tomato<Emphasis Type="Italic"> I-3</Emphasis> gene for fusarium wilt resistance and elimination of a co-segregating resistance gene analogue as a candidate for<Emphasis Type="Italic"> I-3</Emphasis>

The I-3 gene from the wild tomato species Lycopersicon pennellii confers resistance to race 3 of the devastating vascular wilt pathogen Fusarium oxysporum f. sp. lycopersici. As an initial step in a positional cloning strategy for the isolation of I-3, we converted restriction fragment length polymorphism and conserved orthologue set markers, known genes and a resistance gene analogue (RGA) mapping to the I-3 region into PCR-based sequence characterised amplified region (SCAR) and cleaved amplified polymorphic sequence (CAPS) markers. Additional PCR-based markers in the I-3 region were generated using the randomly amplified DNA fingerprinting (RAF) technique. SCAR, CAPS and RAF markers were used for high-resolution mapping around the I-3 locus. The I-3 gene was localised to a 0.3-cM region containing a RAF marker, eO6, and an RGA, RGA332. RGA332 was cloned and found to correspond to a putative pseudogene with at least two loss-of-function mutations. The predicted pseudogene belongs to the Toll interleukin-1 receptor-nucleotide-binding site-leucine-rich-repeat sub-class of plant disease resistance genes. Despite the presence of two RGA332 homologues in L. esculentum, DNA gel blot and PCR analysis suggests that no other homologues are present in lines carrying I-3 that could be alternative candidates for the gene.Communicated by R. Hagemann     

Genetic analysis of resistances to races 1 and 2 of Fusarium oxysporum f. sp. lycopersici from the wild tomato Lycopersicon pennellii

Summary Resistance to race 3 of Fusarium wilt in the wild tomato Lycopersicon pennellii (LA 716) was previously found to be controlled by one major locus, I-3, tightly linked to Got-2 on chromosome 7. This accession was also found to carry resistance to races 1 and 2; a genetic analysis of these resistances is reported in this paper. This analysis proceeded in two steps. First, allelism tests demonstrated that race 1 and 2 resistances carried by L. pennellii were not allelic to the I and I-2 genes originally incorporated into L. esculentum from L. pimpinellifolium. Second, an interspecific backcross with L. pennellii (BC₁) was used to determine the mode of inheritance of these new resistances and their chromosomal location by segregation and linkage analysis. BC₁ responses to each of the races were determined using progeny tests (BC₁S₁). BC₁S₁ plants were inoculated with race 1 or 2 and evaluated after 1 month using a visual disease rating system; mean disease ratings were calculated for each BC₁ individual for each race based on the progeny scores. A bimodal frequency distribution of the BC₁ mean disease ratings was observed for both races, indicating that one major locus controlled resistance in each case. Statistical comparisons of the mean disease ratings of homozygous versus heterozygous individuals at each of 17 segregating enzyme loci were used to map the resistances to races 1 and 2. Tight linkage was detected between the enzyme locus Got-2 and resistances to both races, as was previously reported for the I-3 locus. Therefore, the Got-2 locus can be used as a selectable marker for resistances to all three races. The relationship of these resistances is discussed in the paper. In addition, as previously reported for race 3, significance was also detected for the chromosome segment marked by Aps-2 on chromosome 8 for both races. Currently many cultivars carry I and I-2 resistances to races 1 and 2. Incorporation of the LA 716 resistances to these two races into cultivars may reduce the likelihood of new race development.Florida Agricultural Experiment Station, Journal Series No. R-00205     

RAPD markers associated with salt tolerance in an interspecific cross of tomato (Lycopersicon esculentum×L. pennellii)

This study was conducted to identify randomly amplified polymorphic DNA (RAPD) markers associated with quantitative trait loci (QTLs) conferring salt tolerance during germination in tomato. Germination response of an F₂ population (2000 individuals) of a cross between UCT5 (Lycopersicon esculentum, salt-sensitive) and LA716 (L. pennellii, salt-tolerant) was evaluated at a salt-stress level of 175 mM NaCl+17.5 mM CaCl₂ (water potential ca. –9.5 bars). Germination was scored visually as radicle protrusion at 6-h intervals for 30 consecutive days. Individuals at both extremes of the response distribution (i.e., salt-tolerants and salt-sensitives) were selected. The selected individuals were genotyped for 53 RAPD markers and allele frequencies at each marker locus were determined. The linkage association among the markers was determined using a “Mapmaker” program. Trait-based marker analysis (TBA) identified 13 RAPD markers at eight genomic regions that were associated with QTLs affecting salt tolerance during germination in tomato. Of these genomic regions, five included favorable QTL alleles from LA716, and three included favorable alleles from UCT5. The approximate effects of individual QTLs ranged from 0.46 to 0.82 phenotypic standard deviation. The results support our previous suggestion that salt tolerance during germination in tomato is polygenically controlled. The identification of favorable QTLs in both parents suggests the likelihood of recovering transgressive segregants in progeny derived from these genotypes. Results from this study are discussed in relation to using marker-assisted selection in breeding for salt tolerance. Received: 16 June 1997 / Revision received: 11 August 1997 / Accepted: 2 September 1997     

High resolution genetic and physical mapping of the I-3 region of tomato chromosome 7 reveals almost continuous microsynteny with grape chromosome 12 but interspersed microsynteny with duplications on Arabidopsis chromosomes 1, 2 and 3

The tomato I-3 gene introgressed from the Lycopersicon pennellii accession LA716 confers resistance to race 3 of the fusarium wilt pathogen Fusarium oxysporum f. sp. lycopersici. We have improved the high-resolution map of the I-3 region of tomato chromosome 7 with the development and mapping of 31 new PCR-based markers. Recombinants recovered from L. esculentum cv. M82 × IL7-2 F2 and (IL7-2 × IL7-4) × M82 TC1F2 mapping populations, together with recombinants recovered from a previous M82 × IL7-3 F2 mapping population, were used to position these markers. A significantly higher recombination frequency was observed in the (IL7-2 × IL7-4) × M82 TC1F2 mapping population based on a reconstituted L. pennellii chromosome 7 compared to the other two mapping populations based on smaller segments of L. pennellii chromosome 7. A BAC contig consisting of L. esculentum cv. Heinz 1706 BACs covering the I-3 region has also been established. The new high-resolution map places the I-3 gene within a 0.38 cM interval between the molecular markers RGA332 and bP23/gPT with an estimated physical size of 50–60 kb. The I-3 region was found to display almost continuous microsynteny with grape chromosome 12 but interspersed microsynteny with Arabidopsis thaliana chromosomes 1, 2 and 3. An S-receptor-like kinase gene family present in the I-3 region of tomato chromosome 7 was found to be present in the microsyntenous region of grape chromosome 12 but was absent altogether from the A. thaliana genome. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Quantitative trait loci increasing acylsugars in tomato breeding lines and their impacts on silverleaf whiteflies

Solanum pennellii LA716, a wild relative of tomato, produces acylsugars, an insect resistance compound with activity against many tomato insect pests. Breeding of cultivated tomato using S. pennellii LA716 as a donor parent has led to the development of the elite acylsugar-producing tomato breeding line CU071026. CU071026 contains five introgressed S. pennellii genomic regions, and produces acylsugars at moderate levels that are effective against insect pests. A BC1F1 population was created by crossing the F1 CU071026?×?S. pennellii LA716 with CU071026 as the recurrent parent; this BC1F1 population was used to identify additional regions of the S. pennellii genome important for further improvement of acylsugar production. This population was genotyped with 94 markers in the segregating regions and phenotyped for level of acylsugar production. Using QTLNetwork 2.1 for the detection of quantitative trait loci (QTL) and epistatic interactions, this study identified five QTL for total acylsugar level. Additionally, two epistatic interactions between QTL were found to control significant levels of total acylsugar production. Two of the QTL identified were further evaluated in silverleaf whitefly (Bemisia tabaci) field cage trials using acylsugar breeding lines that differ for the presence/absence of these QTL. While high levels of silverleaf whitefly resistance were observed in all acylsugar breeding lines, lines containing the additional QTL on either chromosomes 6 or 10 had increased levels of total acylsugar production and reduced incidence of whitefly. Acylsugar lines containing the chromosome 6 QTL also had increased density of the type IV glandular trichomes which produce and exude acylsugars.     

Characterization of aLycopersicon esculentum xSolanum lycopersicoides somatic hybrid lacking a glutamate oxaloacetate transaminase isozyme

Morphological, cytological, isozyme and chloroplast DNA analyses were used to determine possible mechanism(s) for the loss of glutamate oxaloacetate transaminase-4 (GOT-4) isozyme activity in a somatic hybrid. Plant 204-1, derived by cell fusion between tomato (Lycopersicon esculentum) andSolanum lycopersicoides, was characterized for bothGot-4 and acid phosphatase-2 (Aps-2), two isozyme loci which are closely linked (recombination 2.5 cM). This hybrid was determined to be chimeric for bothGot-4 andAps-2. TheS. lycopersicoides plant used to provide cells for the fusion was determined to be heterozygous for bothGot-4 andAps-2. Only oneS. lycopersicoides allelic form ofAps-2 andGot-4 was found in plant 204-1. This observation indicated that either the alternative copy of theS. lycopersicoides chromosome region encodingGot-4 andAps-2 is deleted or the entire chromosome is absent. Plant 204-1 was cytologically determined to be aneuploid with approximately 62 chromosomes. Sixty-two somatic hybrids of separate callus origin were analysed for GOT-4 and a high proportion (27%) lacked theS. lycopersicoides form ofGot-4. The loss of this allele and the linkedAps allele most likely occurred in the suspension culture ofS. lycopersicoides used to provide cells for fusion.     

An interspecific linkage map of SSR and intronic polymorphism markers in tomato

Despite the collection and availability of abundant tomato genome sequences, PCR-based markers adapted to large scale analysis have not been developed in tomato species. Therefore, using public genome sequence data in tomato, we developed three types of DNA markers: expressed sequence tag (EST)-derived simple sequence repeat (SSR) markers (TES markers), genome-derived SSR markers (TGS markers) and EST-derived intronic polymorphism markers (TEI markers). A total of 2,047 TES, 3,510 TGS and 674 TEI markers were established and used in the polymorphic analysis of a cultivated tomato (Solanum lycopersicum) ‘LA925’ and its wild relative Solanum pennellii ‘LA716’, parents of the Tomato-EXPEN 2000 mapping population. The polymorphic ratios between parents revealed by the TES, TGS and TEI markers were 37.3, 22.6 and 80.0%, respectively. Those showing polymorphisms were used to genotype the Tomato-EXPEN 2000 mapping population, and a high-density genetic linkage map composed of 1,433 new and 683 existing marker loci was constructed on 12 chromosomes, covering 1,503.1 cM. In the present map, 48% of the mapped TGS loci were located within heterochromatic regions, while 18 and 21% of TES and TEI loci, respectively, were located in heterochromatin. The large number of SSR and SNP markers developed in this study provide easily handling genomic tools for molecular breeding in tomato. Information on the DNA markers developed in this study is available at http://www.kazusa.or.jp/tomato/.     

Bin mapping of tomato diversity array (DArT) markers to genomic regions of <Emphasis Type="Italic">Solanum lycopersicum</Emphasis> × <Emphasis Type="Italic">Solanum pennellii</Emphasis> introgression lines

Marker-trait association studies in tomato have progressed rapidly due to the availability of several populations developed between wild species and domesticated tomato. However, in the absence of whole genome sequences for each wild species, molecular marker methods for whole genome comparisons and fine mapping are required. We describe the development and validation of a diversity arrays technology (DArT) platform for tomato using an introgression line (IL) population consisting of wild Solanum pennellii introgressed into Solanum lycopersicum (cv. M82). A tomato diversity array consisting of 6,912 clones from domesticated tomato and twelve wild tomato/Solanaceous species was constructed. We successfully bin-mapped 990 polymorphic DArT markers together with 108 RFLP markers across the IL population, increasing the number of markers available for each S. pennellii introgression by tenfold on average. A subset of DArT markers from ILs previously associated with increased levels of lycopene and carotene were sequenced, and 44% matched protein coding genes. The bin-map position and order of sequenced DArT markers correlated well with their physical position on scaffolds of the draft tomato genome sequence (SL2.40). The utility of sequenced DArT markers was illustrated by converting several markers in both the S. pennellii and S. lycopersicum phases to cleaved amplified polymorphic sequence (CAPS) markers. Genotype scores from the CAPS markers confirmed the genotype scores from the DArT hybridizations used to construct the bin map. The tomato diversity array provides additional “sequence-characterized” markers for fine mapping of QTLs in S. pennellii ILs and wild tomato species.     

Quantitative trait loci regulating sugar moiety of acylsugars in tomato

Acylsugars are broad-spectrum insect resistance sugar esters produced at very high levels by some accessions of the wild tomato, Solanum pennellii. Transferring acylsugar production from S. pennellii LA716 to cultivated tomato through traditional breeding developed the benchmark acylsugar breeding line CU071026. The base moiety of acylsugars (sucrose vs. glucose) can vary among S. pennellii accessions. Additionally the accession S. pennellii LA716 produces almost exclusively acylglucoses, but the breeding line CU071026 derived from S. pennellii LA716 produces exclusively acylsucroses. This study uses a BC1F1 and a BC1F2 population derived from the cross CU071026 × (CU071026 × S. pennellii LA716) to identify and confirm the action of three quantitative trait loci (QTL) on chromosomes 3, 4, and 11. The QTL on chromosomes 3 and 11 are both required for acylglucose production, while addition of the chromosome 4 QTL affects the level of acylglucose produced in the presence of the QTL on chromosomes 3 and 11. A three-way interaction between these acylglucose QTL was confirmed with a post hoc ANOVA. Identification of these three QTL provides a blueprint for breeding to shift acylsucrose production to acylglucose production in tomato breeding lines. The implications of these QTL and two additional QTL affecting total acylsugar level in the BC1F2 are discussed.     

Advanced backcross QTL analysis of a Lycopersicon esculentum ×Lycopersicon parviflorum cross

Lycopersicon parviflorum is a sexually compatible, wild tomato species which has been largely unutilized in tomato breeding. The Advanced Backcross QTL (AB-QTL) strategy was used to explore this genome for QTLs affecting traits of agronomic importance in an interspecific cross between a tomato elite processing inbred, Lycopersicon esculentum E6203, and the wild species L. parviflorum (LA2133). A total of 170 BC2 plants were genotyped by means of 133 genetic markers (131 RFLPs; one PCR-based marker, I-2, and one morphological marker, u, uniform ripening). Approximately 170 BC3 families were grown in replicated field trials, in California, Spain and Israel, and were scored for 30 horticultural traits. Significant putative QTLs were identified for all traits, for a total of 199 QTLs, ranging from 1 to 19 QTLs detected for each trait. For 19 (70%) traits (excluding traits for which effects of either direction are not necessarily favourable or unfavourable) at least one QTL was identified for which the L. parviflorum allele was associated with an agronomically favourable effect, despite the overall inferior phenotype of the wild species. Received: 14 September 1999 / Accepted: 7 October 1999     

Mapping salt-tolerance genes in tomato (Lycopersicon esculentum) using trait-based marker analysis

The germination responsiveness of an F₂ population derived from the cross Lycopersicon esculentum (UCT5) x L. pennellii (LA716) was evaluated for salt tolerance at two stress levels, 150 mM NaCl + 15 mM CaCl₂ and 200 mM NaCl + 20 mM CaCl₂. Individuals were selected at both tails of the response distribution. The salt-tolerant and salt-sensitive individuals were genotyped at 16 isozyme loci located on 9 of the 12 tomato chromosomes. In addition, an unselected (control) F₂ population was genotyped at the same marker loci, and gene frequencies were estimated in both selected and unselected populations. Trait-based marker analysis was effective in identifying genomic locations (quantitative trait loci, QTLs) affecting salt tolerance in the tomato. Three genomic locations marked by Est-3 on chromosome 1, Prx-7 on chromosome 3, and 6Pgdh-2 and Pgi-1 on chromosome 12 showed significant positive effects, while 2 locations associated with Got-2 on chromosome 7 and Aps-2 on chromosome 8 showed significant negative effects. The identification of genomic locations with both positive and negative effects on this trait suggests the likelihood of recovering transgressive segregants in progeny derived from these parental lines. Similar genomic locations were identified when selection was made either for salt tolerance or salt sensitivity and at both salt-stress treatments. Comparable results were obtained in uni- and bidirectional selection experiments. However, when marker allele gene frequencies in a control population are unknown, bidirectional selection may be more efficient than unidirectional selection in identifying marker-QTL associations. Results from this study are discussed in relationship to the use of molecular markers in developing salt-tolerant tomatoes.     

Examination of genome stability in cultured Lycopersicon

The genetic stability of plants regenerated from either mesophyll protoplasts or leaf slices of the F1 hybrid between Lycopersicon esculentum and L. pennellii was assayed by comparing the ploidy level, leaf morphology and isozyme patterns of the regenerants with their somatic parents. Regenerants from protoplasts were predominantly tetraploid, regenerants from leaf slices were predominantly diploid; both classes of regenerants had isozyme patterns identical to those of the parent plant. Callus was analyzed that grew up from cultures containing fused protoplasts from either irradiated or untreated protoplasts of L. esculentum and L. pennellii. The L. pennellii cell line used was 18 months old and could no longer regenerate. Out of 75 calli scored at 3 isozyme loci, 51 were heterozygous at only one or two of the loci. Irradiation of the two parental lines was not necessary to produce fusion products exhibiting asymmetric expression of parental genes.Abbreviations Got-2 glutamate oxaloacetate transaminase-2 - Pgi-1 phosphoglucoisomerase-1 - Pgm-2 phosphoglucomutase-2     

Tomato cybrids with mitochondrial DNA from Lycopersicon pennelli

Summary Cybrids have been regenerated following protoplast fusion of iodoacetamide-treated leaf mesophyll cells of Lycopersion esculentum cv UC82 and gamma-irradiated cell suspensions of L. pennellii, LA716. The cybrids were recovered in the regenerant population at a frequency of 19%, no selection pressure was applied for the persistence of the donor cytoplasm. The nuclear genotype of ten cybrids was characterized extensively using isozyme markers, cDNA-based restriction fragment length polymorphisms (RFLPs), and the morphology of the plants. No nuclear genetic information from L. pennellii was detected in the cybrids. The organellar genotype of the cybrids was determined using cloned probes and species-specific RFLPs. All the cybrids had inherited the tomato chloroplast genome and had varying amounts of L. pennellii mitochondrial DNA. The cybrids all had a diploid chromosome number of 24, produced pollen, and set seed.     

QTL analysis of pest resistance in the wild tomato Lycopersicon pennellii: QTLs controlling acylsugar level and composition

Some accessions of Lycopersicon pennellii, a wild relative of the tomato Lycopersicon esculentum, are resistant to a number of important pests of cultivated tomato due to the accumulation of acylsugars, which constitute 90% of the exudate of type-IV trichomes in L. pennellii LA716. An interspecific F₂ population, created by the cross L. esculentum x L. pennellii LA 716, was surveyed for acylsugar accumulation and subjected to RFLP/QTL analysis to determine the genomic regions associated with the accumulation of acylglucoses, acylsucroses, and total acylsugars, as well as with acylglucoses as a percentage of total acylsugars (mole percent acylglucoses). Data were analyzed using MAPMAKER/QTL with and without a log₁₀ transformation. A threshold value of 2.4 (default value for MAPMAKER/QTL) was used, as well as 95% empirically derived threshold values. Five genomic regions, two on chromosome 2 and one each on chromosomes 3, 4 and 11, were detected as being associated with one or more aspects of acylsugar production. The L. esculentum allele is partially dominant to the L. pennellii allele in the regions on chromosomes 2 and 11, but the L. pennellii allele is dominant in the region on chromosome 3. Throughout this study, we report the comparative effects of analytical methodology on the identification of acylsugar QTLs. Similarities between our results and published results for the genus Solanum are also discussed.R. W. Doerge · S.-C. Liu · J. P. Kuai contributed equally to the paper, and we ordered randomly     

Identification of quantitative trait loci associated with acylsugar accumulation using intraspecific populations of the wild tomato, Lycopersicon pennellii

 Lycopersicon pennellii LA716, a wild relative of tomato, is resistant to a number of insect pests due to the accumulation of acylsugars exuded from type IV trichomes. These acylsugars are a class of compounds including both acylglucoses and acylsucroses. Intraspecific populations between L. pennellii LA716 and L. pennellii LA1912, the latter an accession that assorts for low-level acylsugar accumulation, were created to study the inheritance of type IV trichome density, acylsugar accumulation levels, percentage of acylsugars that are acylglucoses, and leaf area. The F₂ population was subsequently used to determine genomic regions associated with these traits. The relative proportion of acylglucoses and acylsucroses was found to be largely controlled by a single locus near TG549 on chromosome 3. One locus on chromosome 10 showed significant associations with acylsugar levels. In addition, 1 locus on chromosome 4 showed significant associations with leaf area. Ten additional loci showed modest associations with one or more of the traits examined, 5 of which have been previously reported. Received: 13 March 1997 / Accepted: 19 September 1997     

Isozyme gene markers in Vicia faba L.

Summary This study was conducted to assess the genetic basis of the variability observed for the glutamate oxaloacetate transaminase (GOT), Superoxide dismutase (SOD), esterase (EST), and malate dehydrogenase (MDH) isozyme systems in different open-pollinated Vicia faba varieties. Individual plants showing contrasting zymogram patterns were simultaneously selfed and cross-combined. Crossing was unsuccessful in producing progeny, and only selfed progenies were suitable for genetical analysis of isozyme variability. Three zones of GOT activity were made visible. The isozyme of GOT-2 and GOT-3 zones were dimeric and under the control of three alleles at the Got-2 locus and two alleles at the Got-3 locus, respectively. The isozymes of the GOT-1 zone did not show any variability. Three zones of SOD isozyme activity were made visible. The isozymes occurring in the SOD-1 (chloroplastic isozyme form) and SOD-2 (cytosol isozyme form) zones were dimeric and under the control of two alleles at the Sod-1 and Sod-2 loci. The isozyme visualized in the SOD-3 zone (mitochondrial isozyme form) were tetrameric and under the control of two alleles at the Sod-3 locus. Apparently the isozymes made visible in the most anodal esterase zones EST-1, EST-2, and EST-3 were monomeric, and the occurrence of two alleles at each of two different loci explained the variability observed in the EST-2 and EST-3 zones. For MDH, only two five-banded zymogram pattern types were found, and every selfed progeny showed only one of the two zymogram type, indicating that each individual possessed fixed alleles at the loci controlling MDH isozyme. Got-2, Got-3, Sod-1, Sod-2, and Sod-3 appear to be five new isozyme gene markers that can be useful in Vicia faba breeding for linkage study, varietal fingerprinting, outcrossing rate estimate, and indirect selection for quantitative characters.     

High-resolution linkage analysis and physical characterization of the EIX-responding locus in tomato

An ethylene-inducing xylanase (EIX) from Tricohoderma viride is a potent elicitor of ethylene biosynthesis, localized cell death and other defense responses in specific cultivars of tobacco (Nicotiana tabacum) and tomato (Lycopersicon esculentum). Wild species of tomato, such as Lycopersicon cheesmanii and Lycopersicon pennellii, do not respond to EIX treatment. The F₁ progeny of a L. esculentum×L. cheesmanii and a L. esculentum×L. pennellii cross responded to EIX treatment with an increase in ethylene biosynthesis and the induction of localized cell death. The F₂ progeny of the above mentioned crosses segregated 3:1 (responding:non-responding). We mapped the EIX-responding locus (Eix) to the short arm of chromosome 7 using a population of introgression lines (ILs), containing small RFLP-defined chromosome segments of L. pennellii introgressed into L. esculentum. RFLP analysis of 990 F₂ plants that segregated for the introgressed segment mapped the Eix locus 0.1 cM and 0.9 cM from the flanking markers TG61 and TG131, respectively. Using the marker TG61 we isolated a yeast artificial chromosome (YAC) clone that carries 300-kb DNA segments derived from the Eix region. By mapping the ends of this YAC clone we show that it spans the Eix locus. Thus, positional cloning of the Eix locus appears feasible. Received: 20 March 1999 / Accepted: 30 April 1999     

Quantitative trait loci regulating the fatty acid profile of acylsugars in tomato

Acylsugars are secondary metabolites with proven insect resistance properties that are produced by many Solanaceous species including Solanum pennellii, a wild relative of tomato. The acylsugar chemotypes of S. pennellii varies greatly within its natural range and might be the product of plant/insect coevolution. The S. pennellii accession LA716 was used to transfer increased levels of acylsugar production into the cultivated tomato, resulting in the acylsugar tomato breeding line CU071026. S. pennellii accession LA716 produces high levels of acylsugars with chemotypes that differ greatly from those produced by CU071026 or the trace acylsugars of cultivated tomato. Understanding the genetic regulation of acylsugar chemistry will aid efforts to breed acylsugar production into cultivated tomato, allowing for alteration of both acylsugar base moieties and fatty acid profiles. This study uses a BC1F1 population produced from the cross of S. pennellii LA716 and CU071026 with CU071026 as the recurrent parent to identify QTL that change the fatty acid profile of acylsugars. Multiple QTL and epistatic interactions between QTL were detected including three QTL on chromosomes 2, 5, and 7, which significantly alter the percentage of extended iso-odd branched fatty acids and straight chain fatty acids on the acylsugars. We also report the introgression of one of these QTL, FA 2, into CU071026, resulting in a new tomato line with significantly increased i11:0 as a percentage of the fatty acids in its acylsugars. Candidate genes for these QTL and the impacts of altering acylsugar fatty acid are discussed.     

Development of a set of PCR-based anchor markers encompassing the tomato genome and evaluation of their usefulness for genetics and breeding experiments

Tomato and potato expressed sequence tag (EST) sequences contained in the solanaceae genomics network (SGN) database were screened for simple sequence repeat (SSR) motifs. A total of 609 SSRs were identified and assayed on Solanum lycopersicum LA925 (formerly Lycopersicon esculentum) and S. pennellii LA716 (formerly L. pennellii). The SSRs that did not amplify, gave multiple band products, or did not exhibit a polymorphism that could be readily detected on standard agarose gels in either of these species were eliminated. A set of 76 SSRs meeting these criteria was then placed on the S. lycopersicum (LA925) x S. pennellii (LA716) high-density map. A set of 76 selected cleaved amplified polymorphism (CAP) markers was also developed and mapped onto the same population. These 152 PCR-based anchor markers are uniformly distributed and encompass 95% of the genome with an average spacing of 10.0 cM. These PCR-based markers were further used to characterize S. pennellii introgression lines (Eshed and Zamir, Genetics 141:1147-1162, 1995) and should prove helpful in utilizing these stocks for high-resolution mapping experiments. The majority of these anchor markers also exhibit polymorphism between S. lycopersicum and two wild species commonly used as parents for mapping experiments, S. pimpinellifolium (formerly L. pimpinellifolium) and S. habrochaites (formerly L. hirsutum), indicating that they will be useful for mapping in other interspecific populations. Sixty of the mapped SSRs plus another 49 microsatellites were tested for polymorphism in seven tomato cultivars, four S. lycopersicum var. cerasiforme accessions and eight accessions of five different wild tomato species. Polymorphism information content values were highest among the wild accessions, with as many as 13 alleles detected per locus over all accessions. Most of the SSRs (90%) had accession-specific alleles, with the most unique alleles and heterozygotes usually found in accessions of self-incompatible species. The markers should be a useful resource for qualitative and quantitative trait mapping, marker-assisted selection, germplasm identification, and genetic diversity studies in tomato. The genetic map and marker information can be found on SGN (http://www.sgn.cornell.edu).     

The Ry-fsto gene from Solanum stoloniferum for extreme resistant to Potato virus Y maps to potato chromosome XII and is diagnosed by PCR marker GP122718 in PVY resistant potato cultivars

A novel locus for extreme resistance to Potato virus Y (PVY), Ry-f_sto, was identified on potato chromosome XII. The gene Ry-f_sto has been introgressed from the wild potato species Solanum stoloniferum. Inheritance of Ry-f_sto in the tetraploid potato population Rysto was consistent with the model of a single, dominant gene. Bulked segregant analysis identified an ISSR (inter-simple sequence repeat) marker UBC 857₉₈₀ linked to Ry-f_sto. This marker mapped to linkage group XII of a reference potato RFLP (restriction fragment length polymorphism) map. Chromosome XII specific RFLP markers were converted into PCR-based STS and CAPS markers and tested for linkage with Ry-f_sto in the population Rysto. CAPS marker GP122₇₁₈ was tightly linked to the resistance gene and was successfully used to identify Polish and German cultivars expressing extreme resistance to PVY. This indicates that the source of Ry-f_sto has been widely utilized in various potato breeding programs and can be monitored by a diagnostic marker in marker-assisted selection.