Tomato Species Research Articles

Genome-wide characterization of the cellulose synthase gene superfamily in Solanum lycopersicum

The cellulose synthase gene superfamily, which includes the cellulose synthase (CesA) and cellulose synthase-like (Csl) gene families, plays a vital role in the biosynthesis of cellulose and hemicellulose in plants. However, these genes have not been extensively studied in tomato (Solanum lycopersicum), a model for Solanaceae plants and for fleshy fruit development. Here, we identified and systematically analyzed 38 CesA/Csl family members that contained cellulose synthase domain regions, and categorized their encoded proteins into 6 subfamilies (CesA, CslA, CslB, CslD, CslE, and CslG) based on phylogenetic analysis. Most CesA/Csl genes from tomato are closely related to those from Arabidopsis, but the families have distinct features regarding gene structure, chromosome distribution and localization, phylogeny, and deduced protein sequence, indicating that they arose via different evolutionary process. Furthermore, expression analysis of CesA/Csl genes in different tissues at various developmental stages showed that most CesAs were constitutively expressed with differential expression levels in various organs; three CslD genes were expressed specifically in flowers, and four CesA and five Csl putative genes were preferentially expressed in fruits. Our results provide insight into the general characteristics of the CesA/Csl genes in tomato, and lay the foundation for further functional studies of CesA/Csl genes in tomato and other Solanaceae species.

Agrobacterium tumefaciens-Mediated Transformation of Tomato.

Tomato is both an important food crop and serves as a model plant species that is used for various research investigations including understanding gene function. Transformation is commonly utilized to facilitate these investigations in combination with all the extensive genetic and genomic resources available for tomato. The transformation protocol routinely used in our laboratory has been applied to many different tomato genotypes and relies on Agrobacterium tumefaciens infection of young cotyledon sections. We have used vector systems for overexpression, RNA interference for gene silencing, and CRISPR/Cas9 for genome editing. Vectors used to design gene constructs contained selectable marker genes that conferred resistance to kanamycin, hygromycin, and the herbicide component, bialaphos. The protocol we follow for Agrobacterium-mediated transformation of both cultivated and wild species of tomato is detailed in this chapter.

Identification and Analysis of VTC2 Homologs Encoding the Key Enzyme of L-Ascorbic Acid Biosynthesis in Tomato Species (Solanum Section of Lycopersicon).

The complete nucleotide sequences of 11 wild and cultivated tomato GDP-L-galactose-phosphorylase- 1 homologs (VTC2) were identified and characterized. The overall level of nucleotide variability was 9.19%. Totally 25 out of 54 cDNA SNPs were non-synonymous and resulted in amino acid substitutions. In the group of green-fruited tomato species, more SNPs were detected than in the group of red-fruited species, but the percentage of non-synonymous substitutions in red-fruited tomatoes was significantly higher (66.7% vs. 37.5%). In the translated amino acid sequences, the GDF-L-galactose-hexose-1-phosphate-guanyltransferase domain and the highly conserved HIT-motif were identified and a conserved motif specific for VTC2 of Solanoideae species was detected.

Agromorphological characterization of wild and weedy populations of Physalis angulata in Mexico

Some species of Physalis develop fruits that are appreciated as fruit and as culinary ingredients. Only Physalis peruviana and Physalis philadelphica are grown on a larger scale in America. Physalis angulata is grown on a small scale in Jalisco, Mexico. It is a wild species with extensive cultivation potential in tropical areas and a model of wide interest due to its phytochemical, pharmacological, and nutraceutical properties. The objectives of this study were to carry out the agromorphological characterization of wild and weedy populations of P. angulata, to determine if differences exist between both conditions, and to identify populations with outstanding agronomic attributes. Eleven populations were selected that represent the area of Mexico where this species is traditionally cultivated and consumed. A cultivated population was also used for comparison. The characterization was done with 13 descriptors and multivariate methods. A nested PERMANOVA indicated that no significant differences exist between the wild and weedy condition. The classification and ordination analyses confirmed that the condition does not determine the patterns of variation, nor does it explain the formation of the two groups identified. These analyses also demonstrated the variability in the vegetative attributes and fruit in both conditions. In addition, these analyses showed that four populations exhibit similar agronomic characteristics —a greater number of fruits per plant, of larger size (>14 mm) and more weight (>1.5 g), greater precocity (germination 4–7 days), and higher germination percentage (>95%)— to the cultivated populations. The production per hectare estimated for these populations (11–14 and up to 28 t ha−1) is similar to that recorded for other wild tomato species and slightly lower than that of P. philadelphica. Due to their agronomic attributes, these populations can be part of a core collection for a breeding program. The genetic basis of P. angulata is wide and allows the agronomic evaluation and response to nutrition trials of outstanding genotypes, which will favor greater production.

A Solanum neorickii introgression population providing a powerful complement to the extensively characterized Solanum pennellii population.

Summary We present a complementary resource for trait fine‐mapping in tomato to those based on the intra‐specific cross between cultivated tomato and the wild tomato species Solanum pennellii, which have been extensively used for quantitative genetics in tomato over the last 20 years. The current population of backcross inbred lines (BILs) is composed of 107 lines derived after three backcrosses of progeny of the wild species Solanum neorickii (LA2133) and cultivated tomato (cultivar TA209) and is freely available to the scientific community. These S. neorickii BILs were genotyped using the 10K SolCAP single nucleotide polymorphism chip, and 3111 polymorphic markers were used to map recombination break points relative to the physical map of Solanum lycopersicum. The BILs harbor on average 4.3 introgressions per line, with a mean introgression length of 34.7 Mbp, allowing partitioning of the genome into 340 bins and thereby facilitating rapid trait mapping. We demonstrate the power of using this resource in comparison with archival data from the S. pennellii resources by carrying out metabolic quantitative trait locus analysis following gas chromatography–mass spectrometry on fruits harvested from the S. neorickii BILs. The metabolic candidate genes phenylalanine ammonia‐lyase and cystathionine gamma‐lyase were then tested and validated in F2 populations and via agroinfiltration‐based overexpression in order to exemplify the fidelity of this method in identifying the genes that drive tomato metabolic phenotypes.

The influence of the structure of various isoxazole derivatives on photosynthetic apparatus of tomato plants grown in the field and greenhouse. Effect of various stages of plant growth in different seasons

The aim of this study was to determine how various derivatives of isoxazole affect photosynthetic apparatus of different tomato species grown in a greenhouse and under field conditions. Measurements of chlorophyll fluorescence of photosystem II (PSII) were used as an indicator of the stress induced by isoxazoles on photosynthetic energy conversion. Chlorophyll fluorescence yield provides quantitative information not only on steady-state photosynthesis, but also on various mechanisms of protection against stress-induced damage and the extent to which performance of photosynthesis is limited by photochemical and non-photochemical processes. Measurements were made on tomato plants in various stages of growth (from the 3rd to 15th leaf), in different seasons of the year. The data show that the age of plants does not have a significant influence on Fv/Fm values and it seems that younger plants are more sensitive to the used isoxazole derivatives. Selected isoxazoles did not affect the plant photosynthesis. Practical applications The isoxazole derivatives show inhibitory activity against growth of the fungus pathogens. The objective of this work was to test the ability of the chlorophyll fluorescence measurements as an indicator of the changes induced by isoxazole compounds on photosynthetic energy conversion of tomato plants. Regarding importance of tomato as a very popular and widely consumed all over the world vegetable, the effect of different isoxazole derivatives with different fungicidal activity on tomato plant was examined. The use of some of the tested isoxazolines due to their lack of toxicity for the plants is very promising.

Efficient transient protein expression in tomato cultivars and wild species using agroinfiltration-mediated high expression system.

The new transient protein expression system using thepBYR2HSvector is applicable to several tomato cultivars and wild species with high level of protein expression. Innovation and improvement of effective tools for transient protein expression in plant cells is critical for the development of plant biotechnology. We have created the new transient protein expression system using thepBYR2HSvector that led to about 4mg/g fresh weight of protein expression in Nicotiana benthamiana. In this study, we validated the adaptability of this transient protein expression system by agroinfiltration to leaves and fruits of several tomato cultivars and wild species. Although the GFP protein was transiently expressed in the leaves and fruits of all tomato cultivars and wild species, we observed species-specific differences in protein expression. In particular, GFP protein expression was higher in the leaves and fruits of Micro-Tom, Solanum pimpinellifolium (0043) and S. pimpinellifolium (0049-w1) than in those of cultivars and wild species. Furthermore, Agrobacterium with GABA transaminase enhanced transient expression in tomato fruits of Micro-Tom. Taken together with these results, our system is applicable to several tomato cultivars and species as well as a model tomato, even though characteristics are often different among tomato cultivars or species. Thus, the system is an effective, simple, and valuable tool to achieve rapid transgene expression to examine gene function in tomato plant cells.

Genome-wide analysis of the basic Helix-Loop-Helix (bHLH) transcription factor family in maize

BackgroundIn plants, the basic helix-loop-helix (bHLH) transcription factors play key roles in diverse biological processes. Genome-wide comprehensive and systematic analyses of bHLH proteins have been well conducted in Arabidopsis, rice, tomato and other plant species. However, only few of bHLH family genes have been functional characterized in maize.ResultsIn this study, our genome-wide analysis identified 208 putative bHLH family proteins (ZmbHLH proteins) in maize (Zea mays). We classified these proteins into 18 subfamilies by comparing the ZmbHLHs with Arabidopsis thaliana bHLH proteins. Phylogenetic analysis, conserved protein motifs, and exon-intron patterns further supported the evolutionary relationships among these bHLH proteins. Genome distribution analysis found that the 208 ZmbHLH loci were located non-randomly on the ten maize chromosomes. Further, analysis of conserved cis-elements in the promoter regions, protein interaction networks, and expression patterns in roots, leaves, and seeds across developmental stages, suggested that bHLH family proteins in maize are probably involved in multiple physiological processes in plant growth and development.ConclusionWe performed a genome-wide, systematic analysis of bHLH proteins in maize. This comprehensive analysis provides a useful resource that enables further investigation of the physiological roles and molecular functions of the ZmbHLH transcription factors.

The Genome Sequence of the Wild Tomato Solanum pimpinellifolium Provides Insights Into Salinity Tolerance.

Solanum pimpinellifolium, a wild relative of cultivated tomato, offers a wealth of breeding potential for desirable traits such as tolerance to abiotic and biotic stresses. Here, we report the genome assembly and annotation of S. pimpinellifolium ‘LA0480.’ Moreover, we present phenotypic data from one field experiment that demonstrate a greater salinity tolerance for fruit- and yield-related traits in S. pimpinellifolium compared with cultivated tomato. The ‘LA0480’ genome assembly size (811 Mb) and the number of annotated genes (25,970) are within the range observed for other sequenced tomato species. We developed and utilized the Dragon Eukaryotic Analyses Platform (DEAP) to functionally annotate the ‘LA0480’ protein-coding genes. Additionally, we used DEAP to compare protein function between S. pimpinellifolium and cultivated tomato. Our data suggest enrichment in genes involved in biotic and abiotic stress responses. To understand the genomic basis for these differences in S. pimpinellifolium and S. lycopersicum, we analyzed 15 genes that have previously been shown to mediate salinity tolerance in plants. We show that S. pimpinellifolium has a higher copy number of the inositol-3-phosphate synthase and phosphatase genes, which are both key enzymes in the production of inositol and its derivatives. Moreover, our analysis indicates that changes occurring in the inositol phosphate pathway may contribute to the observed higher salinity tolerance in ‘LA0480.’ Altogether, our work provides essential resources to understand and unlock the genetic and breeding potential of S. pimpinellifolium, and to discover the genomic basis underlying its environmental robustness.

Universal Plant Phosphoproteomics Workflow and Its Application to Tomato Signaling in Response to Cold Stress*

Phosphorylation-mediated signaling transduction plays a crucial role in the regulation of plant defense mechanisms against environmental stresses. To address the high complexity and dynamic range of plant proteomes and phosphoproteomes, we present a universal sample preparation procedure that facilitates plant phosphoproteomic profiling. This advanced workflow significantly improves phosphopeptide identifications, enabling deep insight into plant phosphoproteomes. We then applied the workflow to study the phosphorylation events involved in tomato cold tolerance mechanisms. Phosphoproteomic changes of two tomato species (N135 Green Gage and Atacames) with distinct cold tolerance phenotypes were profiled under cold stress. In total, we identified more than 30,000 unique phosphopeptides from tomato leaves, representing about 5500 phosphoproteins, thereby creating the largest tomato phosphoproteomic resource to date. The data, along with the validation through in vitro kinase reactions, allowed us to identify kinases involved in cold tolerant signaling and discover distinctive kinase-substrate events in two tomato species in response to a cold environment. The activation of SnRK2s and their direct substrates may assist N135 Green Gage tomatoes in surviving long-term cold stress. Taken together, the streamlined approach and the resulting deep phosphoproteomic analyses revealed a global view of tomato cold-induced signaling mechanisms.

Role for Transferrin in Triggering Apoptosis in Helicoverpa armigera Cells Treated with 2-Tridecanone

2-Tridecanone, a plant allelochemical present in a large range of tomato species ( Lycopersicon hirsutum f. glabratum), can induce the expression of Helicoverpa armigera transferrin ( HaTrf), which is necessary for insect growth and development. To gain further insight into the mechanism of HaTrf in response to 2-tridecanone, we measured the iron and H2O2 levels in the hemolymph during exposure to 2-tridecanone and then explored the effect of transferrin downregulation in a H. armigera fat body cell line exposed to 2-tridecanone. We found that the reduction of HaTrf levels via RNA interference caused rapid apoptotic cell death during exposure to 2-tridecanone. There have been no reports about transferrin genes related to apoptosis induced by plant allelochemicals. Our results indicate that HaTrf mediates the inhibition of apoptotic cell death during exposure to 2-tridecanone and provides insight into the importance of transferrin in the interaction between plants and insects.

Tomato stigma exsertion induced by high temperature is associated with the jasmonate signalling pathway.

High temperature (HT) is becoming an increasingly serious factor in limiting crop production with global climate change. During hot seasons, owing to prevailing HT, cultivated tomatoes are prone to exhibiting stigma exsertion, which hampers pollination and causes fruit set failure. However, the underlying regulatory mechanisms of the HT-induced stigma exsertion remain largely unknown. Here, we demonstrate that stigma exsertion induced by HT in cultivated tomato is caused by more seriously shortened stamens than pistils, which is different from the stigma exsertion observed in wild tomato species. Under the HT condition, the different responses of pectin, sugar, expansin, and cyclin cause cell wall remodelling and differentially localized cell division and selective cell enlargement, which further determine the lengths of stamens and pistils. In addition, auxin and jasmonate (JA) are implicated in regulating cell division and cell expansion in stamens and pistils, and exogenous JA instead of auxin treatment can effectively rescue tomato stigma exsertion through regulating the JA/COI1 signalling pathway. Our findings provide a better understanding of stigma exsertions under the HT condition in tomato and uncover a new function of JA in improving plant abiotic stress tolerance.

Germplasm Evaluation of Tomato for Resistance to the Emerging Wilt Pathogen Fusarium Equiseti

Fusarium wilt caused by different Fusarium species is a devastating disease causes heavy loss to tomato plantation worldwide. In this study 13 tomato varieties were screened against F. equiseti to explore the resistance potential of the varieties against the disease. Out of 13 varieties only 2 varieties Roma and Hybrid showed resistance to the disease, while the other 69% were highly susceptible. Based on cluster analysis for genetic diversity it was reported that susceptible varieties are only 8% genetically different and share same genetic pool. We reported that the wild species of tomato Solanum pimpinellifolium (Sp- 2093) showed complete immunity and were remain unaffected having 25% genetic difference with other varieties tested. Thus wild tomato species may provide the source of resistance required to develop resistant variety against the emerging wilt pathogen F. equiseti. The data regarding virluence structure and resisatnt variety that is presented in this study will suport more focused efforts in the management of tomato wilt caused by Fusarium species and that resistant features of wild tomato variety Sp-2093, could be accumulated with other desirable characteristics of different germplasm in one cultivar, which will reduce the chances for new virulent species to evolve.

QTL Mapping of the Shape of Type VI Glandular Trichomes in Tomato.

Glandular trichomes contribute to the high resistance of wild tomato species against insect pests not only thanks to the metabolites they produce but also because of morphological and developmental features which support the high production of these defense compounds. In Solanum habrochaites, type VI trichomes have a distinct spherical shape and a large intercellular storage cavity where metabolites can accumulate and are released upon breaking off of the glandular cells. In contrast, the type VI trichomes of S. lycopersicum have a four-leaf clover shape corresponding to the four glandular cells and a small internal cavity with limited capacity for storage of compounds. To better characterize the genetic factors underlying these trichome morphological differences we created a back-cross population of 116 individuals between S. habrochaites LA1777 and S. lycopersicum var. cerasiforme WVa106. A trichome score that reflects the shape of the type VI trichomes allowing the quantification of this trait was designed. The scores were distributed normally across the population, which was mapped with a total of 192 markers. This resulted in the identification of six quantitative trait locus (QTLs) on chromosomes I, VII, VII, and XI. The QTL on chromosome I with the highest LOD score was confirmed and narrowed down to a 500 gene interval in an advanced population derived from one of the back-cross lines. Our results provide the foundation for the genetic dissection of type VI trichome morphology and the introgression of these trichome traits into cultivated tomato lines for increased insect resistance.Key Message: This work shows that the shape of type VI glandular trichomes in tomato is a genetically defined trait controlled by multiple QTLs with one on chromosome I being the major contributor.

Photosynthetic characteristics in species and interspecific hybrids of tomato

ABSTRACT Gas exchanges in species and interspecific hybrids of tomato in different environments may contribute to the development and selection of genotypes with a higher tolerance to adverse cultivation conditions. This study aimed to assess the photosynthetic characteristics of wild tomato species and the cultivar Redenção, as well as the respective F1 hybrids of interspecific crosses cultivated under two environments. The experimental design was a randomized block design with three replications and the assessment of six wild accessions, one cultivar, and the respective interspecific hybrids under two environments. At 14, 28, 42, 56, and 70 days after transplanting (DAT), gas exchange characteristics were assessed by means of a portable photosynthesis measurement system. The stomatal density of abaxial and adaxial surfaces of first-order leaflets was estimated under a protected cultivation at 56 DAT. We observed a higher influence of wild tomato species and interspecific hybrids on the assessed characteristics when compared to the cultivation environments. The accession ‘LA-716’ and the hybrid ‘Redenção’ × ‘LA-716’ presented the highest water use efficiency and the accessions ‘PI-127826’ and ‘PI-134417’ and the interspecific hybrids ‘Redenção’ × ‘PI-127826’ and ‘Redenção’ × ‘PI-134417’ presented the highest values of CO2 assimilation, transpiration, instantaneous in vivo carboxylation efficiency of Rubisco, and number of stomata on the abaxial leaflet surface. Thus, the descendants of Solanum habrochaites are an interesting alternative to breeding programs that aim to make advances in obtaining strains that exhibit improvement in their photosynthetic characteristics.

Resistance to Tomato Yellow Leaf Curl Virus in Tomato Germplasm.

Tomato yellow leaf curl virus (TYLCV) is a virus species causing epidemics in tomato (Solanum lycopersicum) worldwide. Many efforts have been focused on identification of resistance sources by screening wild tomato species. In many cases, the accession numbers were either not provided in publications or not provided in a consistent manner, which led to redundant screenings. In the current study, we summarized efforts on the screenings of wild tomato species for TYLCV resistance from various publications. In addition, we screened 708 accessions from 13 wild tomato species using different inoculation assays (i.e., whitefly natural infection and Agrobacterium-mediated inoculation) from which 138 accessions exhibited no tomato yellow leaf curl disease (TYLCD) symptoms. These symptomless accessions include 14 accessions from S. arcanum, 43 from S. chilense, 1 from S. chmielewskii, 28 from S. corneliomulleri, 5 from S. habrochaites, 4 from S. huaylasense, 2 from S. neorickii, 1 from S. pennellii, 39 from S. peruvianum, and 1 from S. pimpinellifolium. Most of the screened S. chilense accessions remained symptomless. Many symptomless accessions were also identified in S. arcanum, S. corneliomulleri, and S. peruvianum. A large number of S. pimpinellifolium accessions were screened. However, almost all of the tested accessions showed TYLCD symptoms. Further, we studied allelic variation of the Ty-1/Ty-3 gene in few S. chilense accessions by applying virus-induced gene silencing and allele mining, leading to identification of a number of allele-specific polymorphisms. Taken together, we present a comprehensive overview on TYLCV resistance and susceptibility in wild tomato germplasm, and demonstrate how to study allelic variants of the cloned Ty-genes in TYLCV-resistant accessions.

Inoculation methods and conidial densities of Fusarium oxysporum f. sp. radicis lycoperici in tomato

'Fusarium oxysporum' f.sp. 'radicis-lycopersici' (Forl) is one of the most destructive necrotrophic pathogens affecting tomato crops, causing considerable field and greenhouse yield losses. The use of resistant cultivars is a safe, non-contaminating and reliable control method to eradicate or mitigate this disease. However, it is still necessary to determine the best inoculum density, sufficient to induce levels of resistance or susceptibility. In this study, inoculum concentrations of 3, 5 and 8 x 106 microconidia per mL of 'Forl' were evaluated by root immersion and seed spraying in twenty tomato genotypes (Solanum spp.) in a completely randomized design. The germplasm was mainly introduced tomato species from the Genetic Resources Program of the University of California at Davis, USA. The inoculation was done by immersion of roots and by sprinkling of seeds at the time of sowing. For the inoculation by immersion of roots, tomato seedlings of 15 days emergence were used. The wounds were created in root tips then they submerged into the each conidial suspension. Finally, they transplanted into the plastic pots in a greenhouse. Regarding the inoculation by sprinkling of the seed, 20 seeds of each genotype were placed in plastic pots then sprayed with the corresponding conidial suspension. In both cases, the disease index was calculated. This allowed classifying the genotypes as resistant and susceptible. With the root immersion method all the genotypes evaluated showed susceptible. Significant differences were observed (p<=0.01) between genetic materials at different inoculum doses with the inoculation of seeds. This allowed classification of genotypes Solanum parviflorum LA 1326, 'Solanum chesmanii' f. minor LA1401, 'Solanum chmielewskii' LA1306, 'Solanum pimpinellifolium' LA722, 'Solanum pimpinellifolium' LA2184 as resistant to 'Forl' with disease index of 3, 4, 5, 8 and 12% respectively, at a inoculum concentration of 3x106 microconidia per mL. These genotypes could be included in a genetic breeding program for resistance to crown and root rot caused by 'Forl'.

Molecular characterization and pathogenicity of Alternaria species on wheat and date palms in Oman

This study was conducted to investigate the Alternaria species associated with leaf spot of date palm and wheat in Oman. Out of 98 date palm leaf samples and 146 wheat leaf samples, Alternaria was isolated from 27 and 23% of the samples developing leaf spot symptoms, respectively. Identification of Alternaria isolates using sequences of the internal transcribed spacer region of the ribosomal RNA (ITS rRNA), glyceraldehyde-3-phosphate dehydrogenase (GPDH), translation elongation factor (TEF) and RNA polymerase II subunit (RPB2) genes, showed that the isolates belong to seven Alternaria species or species complexes. A. burnsii - A. tomato and A. arborescens species complexes (58 and 4%, respectively) and A. alternata (38%) were the species recovered from the symptomatic date palm leaves. A. alternata (67%), A. burnsii - A. tomato species complex (15%), A. jacinthicola (3%), A. ventricosa (3%), A. slovaca (6%) and Alternaria caespitosa (6%) were isolated from wheat. Pathogenicity test showed that tested isolates of A. alternata (DPM19, WDK12), A. burnsii - A. tomato species complex (DPM31), A. jacinthicola (WBR4) and A. slovaca (WDK9, WDK7) were pathogenic on date palm, while A. alternata (DPM19, WDK12), A. burnsii - A. tomato species complex (DPM31, WDK11) and A. slovaca (WDK9, WDK7) were pathogenic on wheat. This is the first report of date palm and wheat as new hosts for A. burnsii - A. tomato species complex and the first reports of A. burnsii - A. tomato species complex, A. caespitosa A. slovaca, and A. ventricosa in Oman. The study shows that several species of Alternaria are associated with leaf spot in date palm and wheat in Oman, with some isolates having the ability to cause infection in both hosts.

Development of a New Molecular Marker for the Resistance to Tomato Yellow Leaf Curl Virus.

Tomato yellow leaf curl virus (TYLCV) responsible for tomato yellow leaf curl disease (TYLCD) causes a substantial decrease in tomato (Solanum lycopersicum L.) yield worldwide. The use of resistant variety as a sustainable management strategy has been advocated. Tremendous progress has been made in genetically characterizing the resistance genes (R gene) in tomato. Breeding tomato for TYLCV resistance has been based mostly on Ty-3 as a race-specific resistance gene by introgression originating from wild tomato species relatives. Improvement or development of a cultivar is achievable through the use of marker-assisted selection (MAS). Therefore, precise and easy use of gene-targeted markers would be of significant importance for selection in breeding programs. The present study was undertaken to develop a new marker based on Ty-3 gene sequence that can be used for MAS in TYLCV resistant tomato breeding program. The new developed marker was named ACY. The reliability and accuracy of ACY were evaluated against those of Ty-3 linked marker P6-25 through screening of commercial resistant and susceptible tomato hybrids, and genetic segregation using F2 population derived from a commercial resistant hybrid AG208. With the use of bioinformatics and DNA sequencing analysis tools, deletion of 10 nucleotides was observed in Ty-3 gene sequence for susceptible tomato variety. ACY is a co-dominant indel-based marker that produced clear and strong polymorphic band patterns for resistant plant distinguishing it from its susceptible counterpart. The obtained result correlates with 3:1 segregation ratio of single resistant dominant gene inheritance, which depicted ACY as gene-tag functional marker. This marker is currently in use for screening 968 hybrids varieties and one thousand breeding lines of tomato varieties stocked in Jiangsu Green Port Modern Agriculture Development Company (Green Port). So far, ACY has been used to identify 56 hybrids and 51 breeding lines. These newly detected breeding lines were regarded as potential source of resistance for tomato breeding. This work exploited the sequence of Ty-3 and subsequently contributed to the development of molecular marker ACY to aid phenotypic selection. We thus recommend this marker to breeders, which is suitable for marker-assisted selection in tomato.

Evaluation of temperature stress tolerance in cultivated and wild tomatoes using photosynthesis and chlorophyll fluorescence

Tomato cultivation at lower or higher temperatures than the optimum negatively affects plant growth and development. Large differences in abiotic stress tolerance have been found between Solanum lycopersicum and wild tomato species. Our aim was to compare temperature stress tolerance in cultivated and wild tomato genotypes to identify cold- and heat-tolerant tomatoes for further utilization in tomato breeding. The maintained net photosynthetic rate (PN) and chlorophyll fluorescence was related to the tolerance of tomatoes at temperature stress. The PN and chlorophyll fluorescence of one cultivated tomato (Ly from S. lycopersicum) and six wild tomatoes genotypes (Ha from Solanum habrochaites, Pe from Solanum pennellii, Pi1 and Pi2 from Solanum pimpinellifolium, Pr1 and Pr2 from Solanum peruvianum) grown at low (12 °C) and high (33 °C) temperatures were compared. The PN of four tomato genotypes during temperature stress were lower than the control, but not in Pe, Pr1, and Pr2. The maximum quantum efficiency of photosystem II (Fv/Fm) of the cultivated tomatoes was lower at both 12 and 33 °C than the control using Handy PEA, whereas Fv/Fm using MINI-PAM was lower only at 12 °C. The chlorophyll fluorescence OJIP transient (OJIP curve) revealed differences between temperature stress responses and tomato genotype. With the exception of Pr2, the Fv/Fm in wild tomatoes was unaffected by temperature stress; however, they still maintained clear genotype differences for other physiological traits such as PN, quantum yield of PSII (Fq′/Fm′), electron transport rate, non-photochemical quenching, and the fraction of open PSII centers (qL). These results indicated that the wild tomato varieties Pe and Pr1 had the highest temperature stress tolerance, while the cultivated species was the more sensitive to temperature stress in comparison. In general, the wild tomato genotypes were more tolerant to both cold and heat stress than the cultivated tomato, suggesting that these wild species could be used to uncover underlying mechanisms of temperature stress tolerance and will be promising sources of genetic variability for temperature stress tolerance in breeding programs.