Tomato Species Research Articles

Heritability of the Structures and 13C Fractionation in Tomato Leaf Wax Alkanes: A Genetic Model System to Inform Paleoenvironmental Reconstructions

Leaf wax n-alkanes are broadly used to reconstruct paleoenvironmental information. However, the utility of n-alkanes as a paleoenvironmental proxy may be modulated by the extent to which biological as well as environmental factors influence the structural and isotopic variability of leaf waxes. In paleoclimate applications, there is usually an implicit assumption that most variation of leaf wax traits through a time series can be attributed to environmental change and that biological sources of variability within plant communities are small. For example, changes in hydrology affect the δ2H of waxes via rainwater and the δ13C of leaf waxes by changing plant communities. We measured the degree of genetic control over δ13C variation in leaf waxes within closely related species with an experimental greenhouse growth study. We measured the proportion of variability in structural and isotopic leaf wax traits that is attributable to genetic variation using a set of 76 introgression lines (ILs) between two interfertile Solanum (tomato) species: S. lycopersicum cv M82 (hereafter cv M82) and S. pennellii. Leaves of S. pennellii, a wild desert tomato relative, produced significantly more iso-alkanes than cv M82, a domesticated tomato cultivar adapted to water-replete conditions. We report a methylation index to summarize the ratio of branched (iso- and anteiso-) to total alkanes. Between S. pennellii and cv M82, the iso-alkanes were found to be enriched in 13C by 1.2–1.4‰ over n-alkanes. The broad-sense heritability values (H2) of leaf wax traits describe the degree to which genetic variation contributes to variation of these traits. Variation of individual carbon isotopic compositions of alkanes were of low heritability (H2 = 0.13–0.19), suggesting that most variation in δ13C of leaf waxes in this study can be attributed to environmental variance. This supports the interpretation that variation in the δ13C of wax compounds recorded in sediments reflects paleoenvironmental and vegetation changes. Average chain length (ACL) values of n-alkanes were of intermediate heritability (H2 = 0.30), suggesting that ACL values are more strongly influenced by genetic cues.

Genome-wide sequence variations between wild and cultivated tomato species revisited by whole genome sequence mapping

BackgroundCultivated tomato (Solanum lycopersicum L.) is the second most important vegetable crop after potato and a member of thirteen interfertile species of Solanum genus. Domestication and continuous selection for desirable traits made cultivated tomato species susceptible to many stresses as compared to the wild species. In this study, we analyzed and compared the genomes of wild and cultivated tomato accessions to identify the genomic regions that encountered changes during domestication.ResultsAnalysis was based on SNP and InDel mining of twentynine accessions of twelve wild tomato species and forty accessions of cultivated tomato. Percentage of common SNPs among the accessions within a species corresponded with the reproductive behavior of the species. SNP profiles of the wild tomato species within a phylogenetic subsection varied with their geographical distribution. Interestingly, the ratio of genic SNP to total SNPs increased with phylogenetic distance of the wild tomato species from the domesticated species, suggesting that variations in gene-coding region play a major role in speciation. We retrieved 2439 physical positions in 1594 genes including 32 resistance related genes where all the wild accessions possessed a common wild variant allele different from all the cultivated accessions studied. Tajima’s D analysis predicted a very strong purifying selection associated with domestication in nearly 1% of its genome, half of which is contributed by chromosome 11. This genomic region with a low Tajima’s D value hosts a variety of genes associated with important agronomic trait such as, fruit size, tiller number and wax deposition.ConclusionOur analysis revealed a broad-spectrum genetic base in wild tomato species and erosion of that in cultivated tomato due to recurrent selection for agronomically important traits. Identification of the common wild variant alleles and the genomic regions undergoing purifying selection during cultivation would facilitate future breeding program by introgression from wild species.

GRAFT TAKES OF TOMATO ON OTHER SOLANACEOUS PLANTS

ABSTRACT This paper aimed to assess tomato grafting on different solanaceous species through two grafting methods. Scions were cut from cultivar Santa Cruz Kada seedlings. A fully randomized experimental design was carried out with treatments in a 9 x 2 factorial scheme. As rootstocks, four accessions of mini-tomatoes (0224-53, RVTC 57, RVTC 20 and 6889-50 - Solanum lycopersicum L); two species of wild tomato (Solanum habrochaites var hirsutum ‘PI-127826’ and Solanum pennellii ‘LA716’); other two tomato species [Solanum, cocona (Solanum sessiliflorum) and physalis (Physalis peruviana)] and a control with cultivar Santa Cruz Kada (auto-graft) rootstocks were used. In addition, two grafting methods were evaluated full cleft and approach graft. Fifteen days after grafting, plants were assessed for graft-take percentage; root length; plant height; leaf number; foliar area; root, stem and leaf dry matter; and ratio between shoot and root dry matter. Based on the results, we may state rootstock and grafting interaction had effect on both graft -take rate and plant development. Overall, the studied plants should be recommended as rootstock, except for 6889-50 mini-tomato (S. lycopersicum L.) and S. pennellii. Full cleft grafting was most suitable for cocona and physalis, while the approach method showed better results for the mini-tomato accessions 0224-53, RVTC 57 and RVTC 20, as well as for S. habrochaites.

Trichomes: interaction sites of tomato leaves with biotrophic powdery mildew pathogens

The present study aimed to explore the possibility of using the type I trichomes of tomato (Solanum lycopersicum) to monitor the infection processes of powdery mildews by microscopy. Individual trichome cells of two tomato genotypes were inoculated with pathogenic and non-pathogenic powdery mildew species, Pseudoidium neolycopersici, Erysiphe trifoliorum and Podosphaera xanthii. On the trichome cells of the tomato cultivar Moneymaker, hyphae of the pathogenic Pseudoidium neolycopersici (isolates KTP-03 and KTP-04) grew vigorously; whereas hyphal growth of the non-pathogenic Erysiphe trifoliorum and Podosphaera xanthii ceased after appressorium formation, which was associated with papilla formation and hypersensitive cell death, respectively. Similar infection processes of the tested powdery mildews were seen in Moneymaker epidermal cells. Therefore, tomato trichomes are suitable for analysing, at individual cell level, the infection processes of different pathotypes of powdery mildews and for observing the cytological responses of plants by non-pathogenic powdery mildews. On the other hand, it was observed that both isolates KTP-03 and KTP-04 failed to produce conidiophores on the hyphae elongating on Moneymaker trichomes. Similarly, no conidiophores were produced on the hyphae elongating on trichomes of Solanum peruvianum LA2172, which is resistant to KTP-03 and susceptible to KTP-04. Interestingly, delayed cell death occurred in LA2172 epidermal cells, which were attacked by KTP-03 hyphae elongating from trichomes and conidiophores were formed on new hyphae growing from the leaf epidermal cells. Thus, leaf trichomes and epidermal cells of the wild tomato species LA2172 reacted differently to the avirulent isolate KTP-03.

Homeotic MADS-box genes encoding LeMADS-MC orthologues in wild tomato species (genus Solanum).

New full-length genes encoding the LeMADS-MC transcription factor orthologues were identified and functionally characterized in wild tomato species S. cheesmaniae and S. habrochaites. A comparative analysis of the encoded proteins and LeMADS-MC of the cultivated tomato species S. lycopersicum revealed two major amino acid residues substitutions: V155E in the K-domain of ShaMADS-MC (S. habrochaites) and S80L in the I-region of SchMADS-MC (S. cheesmaniae). Structural differences of the C-terminal regions of MC and the canonical euAP1 proteins indicate possible chromosomal rearrangements in the Solanoideae subfamily, which, however, did not change the main known conserved euAP1 functions.

Comparison of Antioxidant Activity in the Methanolic Peels Extracts of Solanum lycopersocum and Solanum lycopersocum Var. Cerasiforme

Oxidative stress is one of the vital factors which causes serious illness to humans. The reactive oxygen species also accelerates the aging process and antioxidants are crucial in daily diet as it will help to protect body from free radicals and their threats. The current study focuses on the comparison of antioxidant activity in the methanolic peels extract between two tomato species namely Solanum lycopersocum and Solanum lycopersocum var. Cerasiforme (cherry tomato). Tomatoes have abundant antioxidant properties and was determined by DPPH free radical scavenging assay. Methanolic extracts (by maceration method of extraction) of both peels showed high radical scavenging properties, however peels of Solanum lycopersocum var. cerasiforme proved to have higher antioxidant properties. The IC50 result revealed that methanolic peels extract of Solanum lycopersocum var. cerasiforme was found to be 619.14 µg/ml compared to Solanum lycopersocum with 697.16 µg/ml. Thus, the present study reveals that the peels of tomatoes exhibit great potential for antioxidant activity and may be useful for their medicinal and nutritional functions.

Anti-inflammatory and anti-arthritic properties of naringenin via attenuation of NF-κB and activation of the heme oxygenase ﴾HO﴿-1/related factor 2 pathway.

Naringenin, a bioflavonoid present in various species of citrus fruit, tomatoes and grapes, has been shown to have various pharmacological effects. We evaluated the anti-arthritic potential of naringenin in formaldehyde-induced inflammation and complete Freund's adjuvant (CFA)-induced arthritis. For both evaluations, rats were divided into groups of six. Different doses of naringenin (5, 10 and 20mg/kg) were used in the models. Body weight and the arthritic index were assessed. Biochemical and antioxidant parameters were determined. Naringenin dose-dependently reduced joint inflammation, decreasing the joint diameter and inflammatory cell infiltration. Naringenin-treated rats showed an improvement in the synovium redox status (down-regulation of malondialdehyde and glutathione and up-regulation of Catalase (CAT) and superoxide dismutase levels). Naringenin significantly reduced the level of the inflammatory marker TNF-α. Naringenin increased Nrf-2/HO-1 and reduced NF-κB mRNA levels in CFA-treated animal joints. Additionally, naringenin treatment decreased the expression of extracellular matrix degrading enzymes, such as matrix metalloproteinase (MMP-3 and MMP-9), in CFA-induced arthritic rats. We conclude that naringenin exerts anti-arthritic effects by downregulating NF-κB and activating the Nrf-2/HO-1 pathway.

Synthetic acylsugars and their effects on the control of arthropod pests

ABSTRACT One of the main problems facing agriculture is the loss of production as a result of the attack of agricultural pests. Alternative ways to work around this problem are being sought. There are substances called acylsugars that are naturally produced by the wild tomato species S. pennellii and affect arthropod pests. The objectives of this work were to synthesize two acylsugars and assess the biological effect of these on the arthropod pests Bemissia tabaci and Tetranycus urticae. The syntheses were performed via the reactions of glucose and sucrose (saccharose) with acetic anhydride using sodium acetate as the catalyst. The products of these reactions were sucrose octa-acetate and glucose penta-acetate, the structures of which were confirmed by spectroscopic techniques. In a resistance test against the mite, a linear correlation between the concentration of the synthesized substances, and the dislocation of the mite was obtained. A delay in the hatching of the arthropod eggs was observed, causing a mortality rate of approximately 95% in the 1st instar larvae of mites that was confirmed in adults. In the biological tests with Bemisia tabaci, there was a low rate of hatching and emergence, and the effect on the nymphs was the deformation of the emergent adults.

Label-free deep shotgun proteomics reveals protein dynamics during tomato fruit tissues development.

Current innovations in mass-spectrometry-based technologies allow deep coverage of protein expression. Despite its immense value and in contrast to transcriptomics, only a handful of studies in crop plants engaged with global proteome assays. Here, we present large-scale shotgun proteomics profiling of tomato fruit across two key tissues and five developmental stages. A total of 7738 individual protein groups were identified and reliably measured at least in one of the analyzed tissues or stages. The depth of our assay enabled identification of 61 differentially expressed transcription factors, including renowned ripening-related regulators and elements of ethylene signaling. Significantly, we measured proteins involved in 83% of all predicted enzymatic reactions in the tomato metabolic network. Hence, proteins representing almost the complete set of reactions in major metabolic pathways were identified, including the cytosolic and plastidic isoprenoid and the phenylpropanoid pathways. Furthermore, the data allowed us to discern between protein isoforms according to expression patterns, which is most significant in light of the weak transcript-protein expression correspondence. Finally, visualization of changes in protein abundance associated with a particular process provided us with a unique view of skin and flesh tissues in developing fruit. This study adds a new dimension to the existing genomic, transcriptomic and metabolomic resources. It is therefore likely to promote translational and post-translational research in tomato and additional species, which is presently focused on transcription.

First Report of Tomato spotted wilt virus in Eustoma grandiflorum in Korea

HomePlant DiseaseVol. 101, No. 3First Report of Tomato spotted wilt virus in Eustoma grandiflorum in Korea Previous DISEASE NOTES OPENOpen Access licenseFirst Report of Tomato spotted wilt virus in Eustoma grandiflorum in KoreaJ. Y. Yoon, G. S. Choi, and S. K. ChoiJ. Y. YoonSearch for more papers by this author, G. S. ChoiSearch for more papers by this author, and S. K. ChoiSearch for more papers by this authorAffiliationsAuthors and Affiliations J. Y. Yoon G. S. Choi S. K. Choi , Virology Unit, Department of Horticultural and Herbal Environment, National Institute of Horticultural and Herbal Science, RDA, Wanju, Jeollabuk-Do, 55365, Republic of Korea. Published Online:13 Dec 2016https://doi.org/10.1094/PDIS-10-16-1514-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Tomato spotted wilt virus (TSWV) (genus Tospovirus, family Bunyaviridae) was first reported in Korea in 2004 (Choi et al. 2004) and the virus is currently widespread in the country, infecting pepper, tomato, potato, and wild plant species (Choi et al. 2014). TSWV is transmitted by at least 11 species of thrips (e.g., Frankliniella occidentalis), one species of Ceratothripoides, and one species of Scirtothrips. Transmission can also be archived through infected plant sap. Lisianthus (Eustoma grandiflorum) is an herbaceous annual and an emerging flower for weddings, producing eight million cutting flowers in 2014 in Korea. In January 2016, virus-like symptoms including mosaic and wilting followed by necrosis on leaves and branch were observed in lisianthus plants in a greenhouse in Tae-An-gun, Korea. Approximately 10% of lisianthus plants (about 3,000 plants) in the greenhouse showed virus-like foliar symptoms, based on visual estimates. To identify a causal virus, four symptomatic leaf samples of lisianthus plants were analyzed by transmission electron microscopy (TEM) of leaf dip-preparations. Tospovirus-like particles (about 80 to 100 nm in diameter) were observed from all the samples of lisianthus plants. To confirm TEM result, the symptomatic leaf samples were further analyzed using double-antibody sandwich (DAS)-ELISA kits (Agdia, Elkhart, U.S.A.) for the presence of three lisianthus-infecting viruses, such as Bean yellow mosaic virus, Cucumber mosaic virus, and TSWV, as our preliminary survey on flowers. A positive control and a negative control (leaves of healthy a lisianthus plant) were used. DAS-ELISA clearly showed that TSWV was only detected serologically from the naturally infected lisianthus plants. The single infection of TSWV in the symptomatic lisianthus plants was further confirmed by a TSWV-Immunostrip kit (Agdia). To confirm the presence of TSWV alone, RT-PCR products were synthesized for L, M, and S RNA segments using Tospovirus-specific primers and TSWV-specific primers (Batuman et al. 2014; Choi et al. 2014). The expected fragments of 445, 868, and 777 bp were amplified and sequenced (LC191920, LC191921, LC168751). The sequences of each fragment were identical to a consensus sequence, showing 97, 98, and 99% identity with TSWV-L, M, and S RNA (KC494520, HM581941, and KC494482), respectively. These results clearly showed that the results of DAS-ELISA and the TSWV-Immunostrip kit were not due to interspecies cross-reactivity of the virus-specific antibodies. The results of sequence comparisons showed no reassortment between TSWV and another tospovirus. Taken together, a distinct TSWV isolate is the causal agent in the diseased lisianthus plants. To our knowledge, this is the first report of TSWV in lisianthus in Korea. The epidemic nature of TSWV, along with lisianthus production in Korea, warrants monitoring for TSWV in greenhouse production in Korea.

Genetic Diversity and Population Structure of Two Tomato Species from the Galapagos Islands.

Endemic flora of the Galapagos Islands has adapted to thrive in harsh environmental conditions. The wild tomato species from the Galapagos Islands, Solanum cheesmaniae and S. galapagense, are tolerant to various stresses, and can be crossed with cultivated tomato. However, information about genetic diversity and relationships within and between populations is necessary to use these resources efficiently in plant breeding. In this study, we analyzed 3,974 polymorphic SNP markers, obtained through the genotyping-by-sequencing technique, DArTseq, to elucidate the genetic diversity and population structure of 67 accessions of Galapagos tomatoes (compared to two S. lycopersicum varieties and one S. pimpinellifolium accession). Two clustering methods, Principal Component Analysis and STRUCTURE, showed clear distinction between the two species and a subdivision in the S. cheesmaniae group corresponding to geographical origin and age of the islands. High genetic variation among the accessions within each species was suggested by the AMOVA. High diversity in the S. cheesmaniae group and its correlation with the islands of origin were also suggested. This indicates a possible influence of the movement of the islands, from west to east, on the gene flow. Additionally, the absence of S. galapagense populations in the eastern islands points to the species divergence occurring after the eastern islands became isolated. Based on these results, it can be concluded that the population structure of the Galapagos tomatoes collection partially explains the evolutionary history of both species, knowledge that facilitates exploitation of their genetic potential for the identification of novel alleles contributing to stress tolerance.

High-throughput physiological phenotyping and screening system for the characterization of plant-environment interactions.

We present a simple and effective high-throughput experimental platform for simultaneous and continuous monitoring of water relations in the soil-plant-atmosphere continuum of numerous plants under dynamic environmental conditions. This system provides a simultaneously measured, detailed physiological response profile for each plant in the array, over time periods ranging from a few minutes to the entire growing season, under normal, stress and recovery conditions and at any phenological stage. Three probes for each pot in the array and a specially designed algorithm enable detailed water-relations characterization of whole-plant transpiration, biomass gain, stomatal conductance and root flux. They also enable quantitative calculation of the whole plant water-use efficiency and relative water content at high resolution under dynamic soil and atmospheric conditions. The system has no moving parts and can fit into many growing environments. A screening of 65 introgression lines of a wild tomato species (Solanum pennellii) crossed with cultivated tomato (S.lycopersicum), using our system and conventional gas-exchange tools, confirmed the accuracy of the system as well as its diagnostic capabilities. The use of this high-throughput diagnostic screening method is discussed in light of the gaps in our understanding of the genetic regulation of whole-plant performance, particularly under abiotic stress.

The wild tomato species Solanum chilense shows variation in pathogen resistance between geographically distinct populations.

Wild tomatoes are a valuable source of disease resistance germplasm for tomato (Solanum lycopersicum) breeders. Many species are known to possess a certain degree of resistance against certain pathogens; however, evolution of resistance traits is yet poorly understood. For some species, like Solanum chilense, both differences in habitat and within species genetic diversity are very large. Here we aim to investigate the occurrence of spatially heterogeneous coevolutionary pressures between populations of S. chilense. We investigate the phenotypic differences in disease resistance within S. chilense against three common tomato pathogens (Alternaria solani, Phytophthora infestans and a Fusarium sp.) and confirm high degrees of variability in resistance properties between selected populations. Using generalised linear mixed models, we show that disease resistance does not follow the known demographic patterns of the species. Models with up to five available climatic and geographic variables are required to best describe resistance differences, confirming the complexity of factors involved in local resistance variation. We confirm that within S. chilense, resistance properties against various pathogens show a mosaic pattern and do not follow environmental patterns, indicating the strength of local pathogen pressures. Our study can form the basis for further investigations of the genetic traits involved.

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.

Unravelling the strategies used by the wild tomato species Solanum pennellii to confront salt stress: From leaf anatomical adaptations to molecular responses

Despite the genus Solanum include wild species with a high level of tolerance to salinity, the adaptation processes used by these halotolerant species are still poorly understood. Here, the differential responses to salinity of cultivated tomato S. lycopersicum (Sl) and the salt tolerant species S. pennellii (Sp) were studied in order to advance in the understanding of the strategies used by the latter one to confront salt stress, and allow identifying key tolerance traits which could be further introduced in tomato. Several physiological traits, as well as the anatomical structure of leaf and the expression of genes involved in water and Na+ homeostasis, were analysed throughout the time period required by Sp to adapt to salinity (100mM NaCl for 7days). In this period, Sp was able to reduce water loss by regulating transpiration through reduced stomatal density and aperture. Other anatomical adaptations in Sp leaves, including larger and more turgid cells occupied by a giant vacuole, were associated to higher water and Na+ accumulation. Interestingly, a higher basal expression of PIP2;1 aquaporin was also found in leaf of Sp compared to Sl, which could be one of the causes of its better hydric status under salinity. With respect to the genes involved in Na+ homeostasis, our results suggest that SpHKT1;2 in combination with SpSOS1 play an important role in Na+-translocation from root to shoot, and therefore, in the determination of the includer behaviour in the wild species, which is in concordance with the higher transcript levels of Na+ vacuolar transporters SpNHX3 and SpNHX4 in Sp leaves. Overall, these results highlight the necessity of a coordinated regulation of anatomical, physiological and molecular mechanisms in the salt tolerance of the wild species Sp.

In Silico identification of SNP diversity in cultivated and wild tomato species: insight from molecular simulations.

Single Nucleotide Polymorphisms (SNPs), an important source of genetic variations, are often used in crop improvement programme. The present study represented comprehensive In silico analysis of nucleotide polymorphisms in wild (Solanum habrochaites) and cultivated (Solanum lycopersicum) species of tomato to explore the consequence of substitutions both at sequence and structure level. A total of 8978 SNPs having Ts/Tv (Transition/Transversion) ratio 1.75 were identified from the Expressed Sequence Tag (EST) and Next Generation Sequence (NGS) data of both the species available in public databases. Out of these, 1838 SNPs were non-synonymous and distributed in 988 protein coding genes. Among these, 23 genes containing 96 SNPs were involved in traits markedly different between the two species. Furthermore, there were 28 deleterious SNPs distributed in 27 genes and a few of these genes were involved in plant pathogen interaction and plant hormone pathways. Molecular docking and simulations of several selected proteins showed the effect of SNPs in terms of compactness, conformation and interaction ability. Observed SNPs exhibited various types of motif binding effects due to nucleotide changes. SNPs that provide the evidence of differential motif binding and interaction behaviour could be effectively used for the crop improvement program.

Root-to-Shoot Hormonal Communication in Contrasting Rootstocks Suggests an Important Role for the Ethylene Precursor Aminocyclopropane-1-carboxylic Acid in Mediating Plant Growth under Low-Potassium Nutrition in Tomato.

Selection and breeding of rootstocks that can tolerate low K supply may increase crop productivity in low fertility soils and reduce fertilizer application. However, the underlying physiological traits are still largely unknown. In this study, 16 contrasting recombinant inbred lines (RILs) derived from a cross between domestic and wild tomato species (Solanum lycopersicum × Solanum pimpinellifolium) have been used to analyse traits related to the rootstock-mediated induction of low (L, low shoot fresh weight) or high (H, high shoot fresh weight) vigor to a commercial F1 hybrid grown under control (6 mM, c) and low-K (1 mM, k). Based on hormonal and ionomic composition in the root xylem sap and the leaf nutritional status after long-term (7 weeks) exposure low-K supply, a model can be proposed to explain the rootstocks effects on shoot performance with the ethylene precursor aminocyclopropane-1-carboxylic acid (ACC) playing a pivotal negative role. The concentration of this hormone was higher in the low-vigor Lc and Lk rootstocks under both conditions, increased in the sensitive HcLk plants under low-K while it was reduced in the high-vigor Hk ones. Low ACC levels would promote the transport of K vs. Na in the vigorous Hk grafted plants. Along with K, Ca, and S, micronutrient uptake and transport were also activated in the tolerant Hk combinations under low-K. Additionally, an interconversion of trans-zeatin into trans-zeatin riboside would contribute to decrease ACC in the tolerant LcHk plants. The high vigor induced by the Hk plants can also be explained by an interaction of ACC with other hormones (cytokinins and salicylic, abscisic and jasmonic acids). Therefore, Hk rootstocks convert an elite tomato F1 cultivar into a (micro) nutrient-efficient phenotype, improving growth under reduced K fertilization.

Reaction of Solanum (section Lycopersicon) germplasm to Phytophthora capsici

The use of resistant cultivars is one of the most efficient strategies for reducing the amount of pesticides in agricultural crops. Several species of the Solanaceae and Cucurbitaceae families are susceptible to diseases caused by Phytophthora capsici isolates. Even though sources of resistance have been identified in other host plants, reports of resistance to P. capsici in cultivated and wild tomato species [genus Solanum (section Lycopersicon)] germplasm are yet scarce. The main objective of the present work was to characterize the reaction of 244 Solanum (Lycopersicon) accessions to P. capsici under controlled greenhouse experiments. In the first set of experiments, tomato seedlings were inoculated at the collar area with a 3 mL of a spore suspension (2 × 104 zoospores mL−1). Disease incidence (dead plants/total plants) was assessed 14 days after inoculation. The accessions were separated in five well-defined reaction groups: highly resistant (HR), resistant (R), moderately susceptible (MR), susceptible (S), and highly susceptible (HS). The reaction of a group of the ten accessions with the highest levels of resistance was then evaluated against a collection of five P. capsici isolates. Differential reaction was observed among accessions and isolates. The resistant response was host species-dependent with susceptibility being more often found in S. peruvianum accessions, whereas sources of resistance were identified more frequently among accessions of the cultivated tomato (S. lycopersicum).

Weak coordination between leaf structure and function among closely related tomato species

Theory predicts that natural selection should favor coordination between leaf physiology, biochemistry and anatomical structure along a functional trait spectrum from fast, resource-acquisitive syndromes to slow, resource-conservative syndromes. However, the coordination hypothesis has rarely been tested at a phylogenetic scale most relevant for understanding rapid adaptation in the recent past or for the prediction of evolutionary trajectories in response to climate change. We used a common garden to examine genetically based coordination between leaf traits across 19 wild and cultivated tomato taxa. We found weak integration between leaf structure (e.g. leaf mass per area) and physiological function (photosynthetic rate, biochemical capacity and CO2 diffusion), even though all were arrayed in the predicted direction along a 'fast-slow' spectrum. This suggests considerable scope for unique trait combinations to evolve in response to new environments or in crop breeding. In particular, we found that partially independent variation in stomatal and mesophyll conductance may allow a plant to improve water-use efficiency without necessarily sacrificing maximum photosynthetic rates. Our study does not imply that functional trait spectra, such as the leaf economics spectrum, are unimportant, but that many important axes of variation within a taxonomic group may be unique and not generalizable to other taxa.

Interspecific reproductive barriers between sympatric populations of wild tomato species (Solanum section Lycopersicon).

Interspecific reproductive barriers (IRBs) often prevent hybridization between closely related species in sympatry. In the tomato clade (Solanum section Lycopersicon), interspecific interactions between natural sympatric populations have not been evaluated previously. In this study, we assessed IRBs between members of the tomato clade from nine sympatric sites in Peru. Coflowering was assessed at sympatric sites in Peru. Using previously collected seeds from sympatric sites in Peru, we evaluated premating prezygotic (floral morphology), postmating prezygotic (pollen-tube growth), and postzygotic barriers (fruit and seed development) between sympatric species in common gardens. Pollen-tube growth and seed development were examined in reciprocal crosses between sympatric species. We confirmed coflowering of sympatric species at five sites in Peru. We found three types of postmating prezygotic IRBs during pollen-pistil interactions: (1) unilateral pollen-tube rejection between pistils of self-incompatible species and pollen of self-compatible species; (2) potential conspecific pollen precedence in a cross between two self-incompatible species; and (3) failure of pollen tubes to target ovules. In addition, we found strong postzygotic IRBs that prevented normal seed development in 11 interspecific crosses, resulting in seed-like structures containing globular embryos and aborted endosperm and, in some cases, overgrown endothelium. Viable seed and F1 hybrid plants were recovered from three of 19 interspecific crosses. We have identified diverse prezygotic and postzygotic IRBs that would prevent hybridization between sympatric wild tomato species, but interspecific hybridization is possible in a few cases.