Dually biofortified cisgenic tomatoes with increased flavonoids and branched-chain amino acids content.

Higher dietary intakes of flavonoids may have a beneficial role in cardiovascular disease prevention. Additionally, supplementation of branched-chain amino acids (BCAAs) in vegan diets can reduce risks associated to their deficiency, particularly in older adults, which can cause loss of skeletal muscle strength and mass. Most plant-derived foods contain only small amounts of BCAAs, and those plants with high levels of flavonoids are not eaten broadly. Here we describe the generation of metabolically engineered cisgenic tomatoes enriched in both flavonoids and BCAAs. In this approach, coding and regulatory DNA elements, all derived from the tomato genome, were combined to obtain a herbicide-resistant version of an acetolactate synthase (mSlALS) gene expressed broadly and a MYB12-like transcription factor (SlMYB12) expressed in a fruit-specific manner. The mSlALS played a dual role, as a selectable marker as well as being key enzyme in BCAA enrichment. The resulting cisgenic tomatoes were highly enriched in Leucine (21-fold compared to wild-type levels), Valine (ninefold) and Isoleucine (threefold) and concomitantly biofortified in several antioxidant flavonoids including kaempferol (64-fold) and quercetin (45-fold). Comprehensive metabolomic and transcriptomic analysis of the biofortified cisgenic tomatoes revealed marked differences to wild type and could serve to evaluate the safety of these biofortified fruits for human consumption.

Induction of Glandular Trichomes to Control Bemisia tabaci in Tomato Crops: Modulation by the Natural Enemy Nesidiocoris tenuis.

Whitefly-transmitted viruses are one of the biggest threats to tomato (Solanum lycopersicum) growing worldwide. Strategies based on the introgression of resistance traits from wild relatives are promoted to control tomato pests and diseases. Recently, a trichome-based resistance characterizing the wild species Solanum pimpinellifolium was introgressed into a cultivated tomato. An advanced backcross line (BC5S2) exhibiting the presence of acylsugar-associated type IV trichomes, which are lacking in cultivated tomatoes, was effective at controlling whiteflies (Hemiptera: Aleyrodidae) and limiting the spread of whitefly-transmitted viruses. However, at early growth stages, type IV trichome density and acylsugar production are limited; thus, protection against whiteflies and whitefly-transmitted viruses remains irrelevant. In this work, we demonstrate that young BC5S2 tomato plants feeding-punctured by the zoophytophagous predator Nesidiocoris tenuis (Hemiptera: Miridae) displayed an increase (above 50%) in type IV trichome density. Acylsugar production was consistently increased in N. tenuis-punctured BC5S2 plants, which was more likely associated with upregulated expression of the BCKD-E2 gene related to acylsugar biosynthesis. In addition, the infestation of BC5S2 plants with N. tenuis effectively induced the expression of defensive genes involved in the jasmonic acid signaling pathway, resulting in strong repellence to Bemisia tabaci and attractiveness to N. tenuis. Thus, through preplant release of N. tenuis in tomato nurseries carried out in some integrated pest management programs, type IV trichome-expressing plants can be prepared to control whiteflies and whitefly-transmitted viruses at early growth stages. This study emphasizes the advantage of reinforcing constitutive resistance using defense inducers to guarantee robust protection against pests and transmitted viruses.

Crinivirus Tomato Chlorosis Virus Compromises the Control of Tomato Yellow Leaf Curl Virus in Tomato Plants by the Ty-1 Gene.

Tomato yellow leaf curl disease (TYLCD) causes severe damage to tomato crops in warm regions of the world, and is associated with infections of several whitefly (Bemisia tabaci)-transmitted single-stranded (ss)DNA begomoviruses (genus Begomovirus, family Geminiviridae). The most widespread begomovirus isolates associated with TYLCD are those of the type strain of the Tomato yellow leaf curl virus species, known as Israel (TYLCV-IL). The Ty-1 gene is widely used in commercial tomato cultivars to control TYLCV-IL damage, providing resistance to the virus by restricting viral accumulation and tolerance to TYLCD by inhibiting disease symptoms. However, several reports suggest that TYLCV-IL-like isolates are adapting to the Ty-1 gene and are causes of concern for possibly overcoming the provided control. This is the case with TYLCV-IL IS76-like recombinants that have a small genome fragment acquired by genetic exchange from an isolate of Tomato yellow leaf curl Sardinia virus, another begomovirus species associated with TYLCD. Here we show that TYLCV-IL IS76-like isolates partially break down the TYLCD-tolerance provided by the Ty-1 gene and that virulence differences might exist between isolates. Interestingly, we demonstrate that mixed infections with an isolate of the crinivirus (genus Crinivirus, family Closteroviridae) species Tomato chlorosis virus (ToCV), an ssRNA virus also transmitted by B. tabaci and emerging worldwide in tomato crops, boosts the breakdown of the TYLCD-tolerance provided by the Ty-1 gene either with TYLCV-IL IS76-like or canonical TYLCV-IL isolates. Moreover, we demonstrate the incorporation of the Ty-2 gene in Ty-1-commercial tomatoes to restrict (no virus or virus traces, no symptoms) systemic infections of recombinant TYLCV-IL IS76-like and canonical TYLCV-IL isolates, even in the presence of ToCV infections, which provides more robust and durable control of TYLCD.

Begomovirus Tomato Leaf Curl New Delhi Virus Is Seedborne but Not Seed Transmitted in Melon.

Seed transmission can be of considerable relevance to the dissemination of plant viruses in nature and for their prevalence and perpetuation. Long-distance spread of isolates of the begomovirus species Tomato leaf curl New Delhi virus (genus Begomovirus, family Geminiviridae) has recently occurred from Asia to the Middle East and the Mediterranean Basin. Here, we investigated the possible transmission by melon (Cucumis melo L.) seeds of a tomato leaf curl New Delhi virus (ToLCNDV) isolate of the "Spain" strain widely distributed in the Mediterranean area as an alternative mechanism for long-distance spread. PCR amplification detection of ToLCNDV in floral parts and mature seeds of melon plants reveals that this virus is seedborne. "Seedborne" is defined as the ability of a virus to be carried through seeds, which does not necessarily lead to transmission to the next generation. Treatment with a chemical disinfectant significantly reduced the detectable virus associated with melon seeds, suggesting ToLCNDV contamination of the external portion of the seed coat. Also, when the internal fraction of the mature seed (seed cotyledons + embryo) was analyzed by quantitative PCR amplification, ToLCNDV was detectable at low levels, suggesting the potential for viral contamination or infection of the internal portions of seed. However, grow-out studies conducted with melon progeny plants germinated from mature seeds collected from ToLCNDV-infected plants and evaluated at early (1-leaf) or at late (20-leaf) growth stages did not support the transmission of ToLCNDV from seeds to offspring.

Transcriptome analysis of aphids exposed to glandular trichomes in tomato reveals stress and starvation related responses.

Understanding the responses of insect herbivores to plant chemical defences is pivotal for the management of crops and pests. However, the mechanisms of interaction are not entirely understood. In this study, we compared the whole transcriptome gene expression of the aphid Macrosiphum euphorbiae grown on two different varieties of tomato that differ in their inducible chemical defences. We used two isogenic lines of tomato with a shared genetic background that only differ in the presence of type IV glandular trichomes and their associated acylsucrose excretions. This works also reports a de novo transcriptome of the aphid M. euphorbiae. Subsequently, we identified a unique and distinct gene expression profile for the first time corresponding to aphid´s exposure to type IV glandular trichomes and acylsugars. The analysis of the aphid transcriptome shows that tomato glandular trichomes and their associated secretions are highly efficient in triggering stress-related responses in the aphid, and demonstrating that their role in plant defence goes beyond the physical impediment of herbivore activity. Some of the differentially expressed genes were associated with carbohydrate, lipid and xenobiotic metabolisms, immune system, oxidative stress response and hormone biosynthesis pathways. Also, the observed responses are compatible with a starvation syndrome. The transcriptome analysis puts forward a wide range of genes involved in the synthesis and regulation of detoxification enzymes that reveal important underlying mechanisms in the interaction of the aphid with its host plant and provides a valuable genomic resource for future study of biological processes at the molecular level using this aphid.

The role of cuticle in fruit shelf-life.

Ensuring the availability of high-quality fresh fruits requires the development of strategies to maintain prolonged shelf-life. The plant cuticle is a modification of the outer epidermal cell wall and, as such, acts as a barrier with the environment. Understanding how the cuticle naturally changes during postharvest is crucial to address the potential effect of different storage conditions on the cuticle biophysical properties. The impact of different cuticle traits in fruit water loss, its relevance in several fruit-skin disorders, and its participation in postharvest decay caused by pathogens are discussed. Future challenges to study in vivo the physicochemical properties of the cuticle are also addressed.

Genome-wide QTL analysis of tomato fruit cuticle deposition and composition.

Genetics of traits related to fruit cuticle deposition and composition was studied in two red-fruited tomato species. Two mapping populations derived from the cross between the cultivated tomato (Solanum lycopersicum L.) and its closest relative wild species Solanum pimpinellifolium L. were employed to conduct a QTL analysis. A combination of fruit cuticle deposition, components and anatomical traits were investigated and the individual effect of each QTL evaluated. A total of 70 QTLs were identified, indicating that all the cuticle traits analyzed have a complex polygenic nature. A combination of additive and epistatic interactions was observed for all the traits, with positive contribution of both parental lines to most of them. Colocalization of QTLs for various traits uncovered novel genomic regions producing extensive changes in the cuticle. Cuticle density emerges as an important trait since it can modulate cuticle thickness and invagination thus providing a strategy for sustaining mechanical strength without compromising palatability. Two genomic regions, located in chromosomes 1 and 12, are responsible for the negative interaction between cuticle waxes and phenolics identified in tomato fruit. Several candidate genes, including transcription factors and structural genes, are postulated and their expression analyzed throughout development.

Characterization of the detrimental effects of type IV glandular trichomes on the aphid Macrosiphum euphorbiae in tomato.

BACKGROUND: Glandular trichomes are essential in plants' defence against pests however, the mechanisms of action are not completely understood. While there is considerable evidence of feeding and movement impairment by trichomes, the effect on other traits is less clear. We combined laboratory and greenhouse experiments with molecular analysis to understand how glandular trichomes affect the behavior, population growth, and the expression of biomarkers involved in detoxification, primary metabolism, and developmental pathways of the aphid Macrosiphum euphorbiae. We used two isogenic tomato lines that differ in the presence of type IV glandular trichomes and production of acylsucroses; i.e.,Solanum lycopersicum cv. 'Moneymaker' and an introgressed line from Solanum pimpinellifolium (with trichomes type IV). RESULTS: Type IV glandular trichomes affected host selection and aphid proliferation with aphids avoiding, and showing impaired multiplication on the genotype with trichomes. The exposure to type IV glandular trichomes resulted in the overexpression of detoxication markers (i.e., Hsp70, Hsp17, Hsp10); the repression of the energetic metabolism (GAPDH), and the activation of the ecdysone pathway; all these, underlying the key adaptations and metabolic trade-offs in aphids exposed to glandular trichomes. CONCLUSION: Our results demonstrate the detrimental effect of glandular trichomes (type IV) on the aphid and put forward their mode of action. Given the prevalence of glandular trichomes in wild and cultivated Solanaceae; and of the investigated molecular biomarkers in insects in general, our results provide relevant mechanisms to understand the effect of trichomes not only on herbivorous insects but also on other trophic levels.

Host Plant Resistance to Bemisia tabaci to Control Damage Caused in Tomato Plants by the Emerging Crinivirus Tomato Chlorosis Virus.

Tomato chlorosis virus (genus Crinivirus, family Closteroviridae) (ToCV) is rapidly emerging, causing increased damage to tomato production worldwide. The virus is transmitted in a semipersistent manner by several whitefly (Hemiptera: Aleyrodidae) species and is expanding its geographical and host ranges associated with the emergence of whiteflies of the Bemisia tabaci complex. Control is based essentially on intensive insecticide applications against the insect vector but is largely ineffective. No virus-resistant or tolerant commercial tomato cultivars are available. Recently, a B. tabaci-resistant tomato line based on the introgression of type IV leaf glandular trichomes and secretion of acylsucroses from the wild tomato Solanum pimpinellifolium was shown to effectively control the spread of tomato yellow leaf curl virus, a begomovirus (genus Begomovirus, family Geminiviridae) persistently transmitted by B. tabaci. As short acquisition and transmission periods are associated to the semipersistent transmission of ToCV, its possible control by means of the B. tabaci-resistant tomato could be compromised. Moreover, if the antixenosis effect of the resistance trait present in those tomato plants results in increased B. tabaci mobility, an increased ToCV spread might even occur. We demonstrated, however, that the use of acylsugar-producing B. tabaci-resistant tomatoes effectively controls ToCV spread compared to a near-isogenic line without type IV trichomes and acylsugar secretion. No increase in the primary ToCV spread is observed, and secondary spread could be reduced significantly decreasing the incidence of this virus. The possible use of host plant resistance to whiteflies to limit spread of ToCV opens up new alternatives for a more effective control of this virus to reduce the damage caused in tomato crops.

An Acylsucrose-Producing Tomato Line Derived from the Wild Species Solanum pimpinellifolium Decreases Fitness of the Whitefly Trialeurodes vaporariorum.

A combination of biological control and host plant resistance would be desirable for optimally controlling the greenhouse whitefly, Trialeurodes vaporariorum in tomato crops. Whitefly settlement preference, oviposition, and survivorship were evaluated on ABL 10-4 and 'Moneymaker', two nearly-isogenic tomato lines with, and without, whitefly-resistance traits based on type IV leaf glandular trichomes derived from the tomato wild species Solanum pimpinellifolium, respectively. Significantly reduced preference of T. vaporariorum adult whiteflies for ABL 10-4 leaves was observed. Moreover, T. vaporariorum altered its abaxial-adaxial settling performance on leaves of ABL 10-4 plants. A significantly lower tendency to settle on abaxial leaf surface was observed in ABL 10-4 compared to Moneymaker plants. Furthermore, T. vaporariorum deposited fewer eggs and exhibited a significantly reduced egg to adult survivorship in ABL 10-4 than in Moneymaker plants. Therefore, reduced fitness and distorted performance were observed for T. vaporariorum on ABL 10-4 tomato plants supporting that type IV leaf glandular trichomes might protect them from this pest and, indirectly, from the viruses it transmits.

Use of Systemic Acquired Resistance and Whitefly Optical Barriers to Reduce Tomato Yellow Leaf Curl Disease Damage to Tomato Crops.

Epidemics of tomato yellow leaf curl disease (TYLCD) caused by tomato yellow leaf curl-like begomoviruses (genus Begomovirus, family Geminiviridae) severely damage open field and protected tomato crops worldwide. Intensive application of insecticides against the whitefly vector Bemisia tabaci is generally used as control strategy to reduce TYLCD impact. This practice, however, is frequently ineffective and has a negative impact on the environment and human health. TYLCD-resistant varieties are commercially available, but cultivation of susceptible traditional tasting ones is also requested if possible. For susceptible tomatoes, here we show that using whitefly optical barriers by means of UV-blocking plastics in protected crops can contribute to reducing TYLCD damage and increasing commercial fruit yield. Moreover, induction of systemic acquired resistance by application of the elicitor of plant defense acibenzolar-S-methyl was effective to reduce yield losses when viral pressure was moderate. Interestingly, combining both practices in protected tomato crops can result in a significant TYLCD control. Therefore, these control practices are proposed to be used commercially as management alternatives to include in integrated management of TYLCD.

Measles Virus Hemagglutinin epitopes immunogenic in natural infection and vaccination are targeted by broad or genotype-specific neutralizing monoclonal antibodies.

Measles virus (MV) remains a leading cause of vaccine-preventable deaths in children. Protection against MV is associated with neutralizing antibodies that preferentially recognize the viral hemagglutinin (MV-H), and to a lesser extent, the fusion protein (MV-F). Although MV is serologically monotypic, 24 genotypes have been identified. Here we report three neutralization epitopes conserved in the more prevalent circulating MV genotypes, two located in the MV-H receptor binding site (RBS) (antigenic site III) and a third in MV-H/MV-F interphase (antigenic site Ia) which are essential for MV multiplication. In contrast, two MV-H neutralization epitopes, showed a genotype-specific neutralization escape due to a single amino acid change, that we mapped in the "noose" antigenic site, or an enhanced neutralization epitope (antigenic site IIa). The monoclonal antibody (mAb) neutralization potency correlated with its binding affinity and was mainly driven by kinetic dissociation rate (koff). We developed an immunoassay for mAb binding to MV-H in its native hetero-oligomeric structure with MV-F on the surface of a MV productive steady-state persistently infected (p.i.) human cell lines, and a competitive-binding assay with serum from individuals with past infection by different MV genotypes. Binding assays revealed that a broad neutralization epitope, in RBS antigenic site, a genotype specific neutralization epitopes, in noose and IIa sites, were immunogenic in natural infection and vaccination and may elicit long-lasting humoral immunity that might contribute to explain MV immunogenic stability. These results support the design of improved measles vaccines, broad-spectrum prophylactic or therapeutic antibodies and MV-used in oncolytic therapies.

QTL mapping of fruit mineral contents provides new chances for molecular breeding of tomato nutritional traits.

KEY MESSAGE: Agronomical characterization of a RIL population for fruit mineral contents allowed for the identification of QTL controlling these fruit quality traits, flanked by co-dominant markers useful for marker-assisted breeding. Tomato quality is a multi-variant attribute directly depending on fruit chemical composition, which in turn determines the benefits of tomato consumption for human health. Commercially available tomato varieties possess limited variability in fruit quality traits. Wild species, such as Solanum pimpinellifolium, could provide different nutritional advantages and can be used for tomato breeding to improve overall fruit quality. Determining the genetic basis of the inheritance of all the traits that contribute to tomato fruit quality will increase the efficiency of the breeding program necessary to take advantage of the wild species variability. A high-density linkage map has been constructed from a recombinant inbred line (RIL) population derived from a cross between tomato Solanum lycopersicum and the wild-relative species S. pimpinellifolium. The RIL population was evaluated for fruit mineral contents during three consecutive growing seasons. The data obtained allowed for the identification of main QTL and novel epistatic interaction among QTL controlling fruit mineral contents on the basis of a multiple-environment analysis. Most of the QTL were flanked by candidate genes providing valuable information for both tomato breeding for new varieties with novel nutritional properties and the starting point to identify the genes underlying these QTL, which will help to reveal the genetic basis of tomato fruit nutritional properties.

Identification, introgression, and validation of fruit volatile QTLs from a red-fruited wild tomato species.

Volatile organic compounds (VOCs) are major determinants of fruit flavor, a primary objective in tomato breeding. A recombinant inbred line (RIL) population consisting of 169 lines derived from a cross between Solanum lycopersicum and a red-fruited wild tomato species Solanum pimpinellifolium accession (SP) was characterized for VOCs in three different seasons. Correlation and hierarchical cluster analyses were performed on the 52 VOCs identified, providing a tool for the putative assignation of individual compounds to metabolic pathways. Quantitative trait locus (QTL) analysis, based on a genetic linkage map comprising 297 single nucleotide polymorphisms (SNPs), revealed 102 QTLs (75% not described previously) corresponding to 39 different VOCs. The SP alleles exerted a positive effect on most of the underlying apocarotenoid volatile QTLs-regarded as desirable for liking tomato-indicating that alleles inherited from SP are a valuable resource for flavor breeding. An introgression line (IL) population developed from the same parental genotypes provided 12 ILs carrying a single SP introgression and covering 85 VOC QTLs, which were characterized at three locations. The results showed that almost half of the QTLs previously identified in the RILs maintained their effect in an IL form, reinforcing the value of these QTLs for flavor/aroma breeding in cultivated tomato.

A Jasmonate-Inducible Defense Trait Transferred from Wild into Cultivated Tomato Establishes Increased Whitefly Resistance and Reduced Viral Disease Incidence.

Whiteflies damage tomatoes mostly via the viruses they transmit. Cultivated tomatoes lack many of the resistances of their wild relatives. In order to increase protection to its major pest, the whitefly Bemisia tabaci and its transmitted Tomato Yellow Leaf Curl Virus (TYLCV), we introgressed a trichome-based resistance trait from the wild tomato Solanum pimpinellifolium into cultivated tomato, Solanum lycopersicum. The tomato backcross line BC5S2 contains acylsucrose-producing type-IV trichomes, unlike cultivated tomatoes, and exhibits increased, yet limited protection to whiteflies at early development stages. Treatment of young plants with methyl jasmonate (MeJA) resulted in a 60% increase in type-IV trichome density, acylsucrose production, and enhanced resistance to whiteflies, leading to 50% decrease in the virus disease incidence compared to cultivated tomato. Using transcriptomics, metabolite analysis, and insect bioassays we established the basis of this inducible resistance. We found that MeJA activated the expression of the genes involved in the biosynthesis of the defensive acylsugars in young BC5S2 plants leading to enhanced chemical defenses in their acquired type-IV trichomes. Our results show that not only constitutive but also these inducible defenses can be transferred from wild into cultivated crops to aid sustainable protection, suggesting that conventional breeding strategies provide a feasible alternative to increase pest resistance in tomato.

Exploring New Alleles Involved in Tomato Fruit Quality in an Introgression Line Library of Solanum pimpinellifolium.

We have studied a genomic library of introgression lines from the Solanum pimpinellifolium accession TO-937 into the genetic background of the "Moneymaker" cultivar in order to evaluate the accession's breeding potential. Overall, no deleterious phenotypes were observed, and the plants and fruits were phenotypically very similar to those of "Moneymaker," which confirms the feasibility of translating the current results into elite breeding programs. We identified chromosomal regions associated with traits that were both vegetative (plant vigor, trichome density) and fruit-related (morphology, organoleptic quality, color). A trichome-density locus was mapped on chromosome 10 that had not previously been associated with insect resistance, which indicates that the increment of trichomes by itself does not confer resistance. A large number of quantitative trait loci (QTLs) have been identified for fruit weight. Interestingly, fruit weight QTLs on chromosomes 1 and 10 showed a magnitude effect similar to that of QTLs previously defined as important in domestication and diversification. Low variability was observed for fruit-shape-related traits. We were, however, able to identify a QTL for shoulder height, although the effects were quite low, thus demonstrating the suitability of the current population for QTL detection. Regarding organoleptic traits, consistent QTLs were detected for soluble solid content (SSC). Interestingly, QTLs on chromosomes 2 and 9 increased SSC but did not affect fruit weight, making them quite promising for introduction in modern cultivars. Three ILs with introgressions on chromosomes 1, 2, and 10 increased the internal fruit color, making them candidates for increasing the color of modern cultivars. Comparing the QTL detection between this IL population and a recombinant inbred line population from the same cross, we found that QTL stability across generations depended on the trait, as it was very high for fruit weight but low for organoleptic traits. This difference in QTL stability may be due to a predominant additive gene action for QTLs involved in fruit weight, whereas epistatic and genetic background interactions are most likely important for the other traits.

Improving agronomic water use efficiency in tomato by rootstock-mediated hormonal regulation of leaf biomass.

Water availability is the most important factor limiting food production, thus developing new scientific strategies to allow crops to more efficiently use water could be crucial in a world with a growing population. Tomato is a highly water consuming crop and improving its water use efficiency (WUE) implies positive economic and environmental effects. This work aimed to study and exploit root-derived hormonal traits to improve WUE in tomato by grafting on selected rootstocks. Firstly, root-related hormonal parameters associated to WUE were identified in a population of recombinant inbred lines (RILs) derived from the wild tomato species Solanum pimpinellifolium. A principal component analysis (PCA) revealed that some hormonal traits were associated with productivity (plant biomass and photosynthesis) and WUE in the RIL population. Leaf ABA concentration was associated to the first component (PC1) of the PCA, which explained a 60% of the variance in WUE, while the ethylene precursor ACC and the ratio ACC/ABA were also associated to PC1 but in the opposite direction. Secondly, we selected RILs according to their extreme biomass (high, B, low, b) and water use (high, W, low, w), and studied the differential effect of shoot and root on WUE by reciprocal grafting. In absence of any imposed stress, there were no rootstock effects on vegetative shoot growth and water relations. Finally, we exploited the previously identified root-related hormonal traits by grafting a commercial tomato variety onto the selected RILs to improve WUE. Interestingly, rootstocks that induced low biomass and water use, 'bw', improved fruit yield and WUE (defined as fruit yield/water use) by up to 40% compared to self-grafted plants. Although other hormonal factors appear implicated in this response, xylem ACC concentration seems an important root-derived trait that inhibits leaf growth but does not limit fruit yield. Thus tomato WUE can be improved exploiting rootstock-derived hormonal signals which control leaf growth.

Wide-genome QTL mapping of fruit quality traits in a tomato RIL population derived from the wild-relative species Solanum pimpinellifolium L.

KEY MESSAGE: QTL and candidate genes associated to fruit quality traits have been identified in a tomato genetic map derived from Solanum pimpinellifolium L., providing molecular tools for marker-assisted breeding. The study of genetic, physiological, and molecular pathways involved in fruit development and ripening has considered tomato as the model fleshy-fruited species par excellence. Fruit quality traits regarding organoleptic and nutritional properties are major goals for tomato breeding programs since they largely decide the acceptance of tomato in both fresh and processing markets. Here we report the genetic mapping of single-locus and epistatic quantitative trait loci (QTL) associated to the fruit size and content of sugars, acids, vitamins, and carotenoids from the characterization of a RIL population derived from the wild-relative Solanum pimpinellifolium TO-937. A genetic map composed of 353 molecular markers including 13 genes regulating fruit and developmental traits was generated, which spanned 1007 cM with an average distance between markers of 2.8 cM. Genetic analyses indicated that fruit quality traits analyzed in this work exhibited transgressive segregation and that additive and epistatic effects are the major genetic basis of fruit quality traits. Moreover, most mapped QTL showed environment interaction effects. FrW7.1 fruit size QTL co-localized with QTL involved in soluble solid, vitamin C, and glucose contents, dry weight/fresh weight, and most importantly with the Sucrose Phosphate Synthase gene, suggesting that polymorphisms in this gene could influence genetic variation in several fruit quality traits. In addition, 1-deoxy-D-xylulose 5-phosphate synthase and Tocopherol cyclase genes were identified as candidate genes underlying QTL variation in beta-carotene and vitamin C. Together, our results provide useful genetic and molecular information regarding fruit quality and new chances for tomato breeding by implementing marker-assisted selection.

Recessive Resistance Derived from Tomato cv. Tyking-Limits Drastically the Spread of Tomato Yellow Leaf Curl Virus.

The tomato yellow leaf curl disease (TYLCD) causes severe damage to tomato (Solanum lycopersicum L.) crops throughout tropical and subtropical regions of the world. TYLCD is associated with a complex of single-stranded circular DNA plant viruses of the genus Begomovirus (family Geminiviridae) transmitted by the whitefy Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae). The tomato inbred line TX 468-RG is a source of monogenic recessive resistance to begomoviruses derived from the hybrid cv. Tyking F1. A detailed analysis of this germplasm source against tomato yellow leaf curl virus-Israel (TYLCV-IL), a widespread TYLCD-associated virus, showed a significant restriction to systemic virus accumulation even under continuous virus supply. The resistance was effective in limiting the onset of TYLCV-IL in tomato, as significantly lower primary spread of the virus occurred in resistant plants. Also, even if a limited number of resistant plants could result infected, they were less efficient virus sources for secondary spread owing to the impaired TYLCV-IL accumulation. Therefore, the incorporation of this resistance into breeding programs might help TYLCD management by drastically limiting TYLCV-IL spread.

Measles virus genetic evolution throughout an imported epidemic outbreak in a highly vaccinated population.

Measles virus circulates endemically in African and Asian large urban populations, causing outbreaks worldwide in populations with up-to-95% immune protection. We studied the natural genetic variability of genotype B3.1 in a population with 95% vaccine coverage throughout an imported six month measles outbreak. From first pass viral isolates of 47 patients we performed direct sequencing of genomic cDNA. Whilst no variation from index case sequence occurred in the Nucleocapsid gene hyper-variable carboxy end, in the Hemagglutinin gene, main target for neutralizing antibodies, we observed gradual nucleotide divergence from index case along the outbreak (0% to 0.380%, average 0.138%) with the emergence of transient and persistent non-synonymous and synonymous mutations. Little or no variation was observed between the index and last outbreak cases in Phosphoprotein, Nucleocapsid, Matrix and Fusion genes. Most of the H non-synonymous mutations were mapped on the protein surface near antigenic and receptors binding sites. We estimated a MV-Hemagglutinin nucleotide substitution rate of 7.28 × 10-6 substitutions/site/day by a Bayesian phylogenetic analysis. The dN/dS analysis did not suggest significant immune or other selective pressures on the H gene during the outbreak. These results emphasize the usefulness of MV-H sequence analysis in measles epidemiological surveillance and elimination programs, and in detection of potentially emergence of measles virus neutralization-resistant mutants.