Wild Solanum Species Research Articles

Solanum palinacanthum: broad-spectrum resistance to root-knot nematodes (Meloidogyne spp.).

Root-knot nematodes (RKN, Meloidogyne spp.) are harmful phytophagous pests of Solanum spp. Some RKN species are becoming worldwide problems because of their virulence to RKN-resistant Solanum species. A new Solanum species carrying broad-spectrum resistance to Meloidogyne spp. is required for the effective management of this pest. Here we sought to determine the host suitability of RKN to Solanum palinacanthum, a wild Solanum species, and to evaluate its potential effectiveness in RKN management. We identified an RKN-resistant Solanum species, S. palinacanthum, by screening Solanum accessions. We tested its spectrum of resistance to common Meloidogyne spp. in Japan. In pot tests inoculated with second-stage juveniles, S. palinacanthum showed poor host suitability for Melidogyne incognita, M. arenaria genotypes A2-J and A2-O, M. javanica and M. hapla, indicating broad-spectrum resistance to RKN. The development of M. incognita within S. palinacanthum roots was significantly poorer than that in susceptible S. melongena and S. lycopersicum at 10 and 21 days after inoculation. Microplot tests confirmed that the number of second-stage juveniles in plots where S. palinacanthum grew and root galling of the root system were significantly lower than those of susceptible S. melongena, suggesting that the resistance could be used to manage RKN under field conditions. S. palinacanthum showed poor host suitability to all Meloidogyne spp. tested in this study, and it thus has the potential to be used as a genetic resource with broad-spectrum RKN resistance, and it could be effective against multiple RKN species in a field. © 2020 Society of Chemical Industry.

RESISTANCE OF WILD SOLANUM SPECIES AND HYBRIDS TO EARLY AND LATE BLIGHT

Early and late blight are the most harmful diseases of the potato causing significant economic losses in many regions where this crop is cultivated. The search for donors with complex resistance to these diseases is a priority for potato breeding. Twenty-one accession s of wild Solanum species and interspecific hybrids with various pedigrees were studied. The reaction of plants to the infection caused by Alternaria solani and Phytophthora infestans was assessed separately in the laboratory test using the inoculation of leaf disks and leaf fractions of the potato accessions with a suspension of pathogen conidia and zoospores, respectively. All studied potato accessions showed the symptoms of early and late blight after the inoculation, but significantly varied in sensitivity to the pathogens. Inoculation caused by A. solani led to the development of necrosis of the analyzed potato accessions, covering from 1.2 % to 11.5 % of leaf disk area. After the inoculation with P. infestans the intensity of the symptom development on the leaf fractions of all analyzed potato accessions varied from 3 to 9 points on a 9-point scale. Six potato phenotypes represented by one Solanum species and 5 interspecific hybrids with complex resistance to early and late blight were identified.

Evaluation of Wild Potato Germplasm for Tuber Starch Content and Nitrogen Utilization Efficiency.

Potato wild relatives provide a considerable source of variation for important traits in cultivated potato (Solanum tuberosum L.) breeding. This study evaluates the variation of tuber starch content and nitrogen utilization efficiency (NutE) in wild potato germplasm. For the experiments regarding starch content, 28 accessions of ten different tuber-bearing wild Solanum-species were chosen, and in vitro plantlets were raised from seeds. Twenty plantlets (= genotypes) per accession were then cultivated in the greenhouse until natural senescence and tuber starch content was determined. The average tuber starch content across all genotypes tested was 21.7% of fresh mass. Contents above 28% of fresh mass were found in 50 genotypes, belonging to the species S. chacoense, S. commersonii, S. jamesii, and S. pinnatisectum. Subsequently, 22 wild genotypes revealing high tuber starch contents and four modern varieties of cultivated potato were studied as in vitro plantlets under optimal and low N supply (30 and 7.5 mmol L−1 N). Low N supply lead to a genotype-dependent reduction of shoot dry mass between 13 and 46%. The majority of the wild types also reduced root dry mass by 26 to 62%, while others maintained root growth and even exceeded the NutE of the varieties under low N supply. Thus, wild potato germplasm appears superior to cultivars in terms of tuber starch contents and N utilization efficiency, which should be investigated in further studies.

Solanum gourlayi\u2014a Source of Cyst Nematode Resistance in Potato Breeding

The potato cyst nematodes (PCN) Globodera rostochiensis and G. pallida are among the most important pests causing significant yield loss in potato production. Cultivating resistant cultivars of potato is the most effective and environmentally safe method for protecting potato crops against nematodes. However, widespread cultivation of cultivars resistant to G. rostochiensis can affect the reproduction of G. pallida. Therefore, breeding for resistance to nematodes remains among the major aims of potato breeding programmes. Many wild Solanum species could be valuable sources of nematode resistance. This study examined the resistance to G. pallida identified in two accessions of the wild species Solanum gourlayi. Both accessions demonstrated resistance to pathotypes Pa2 and Pa3, but show asymmetric distribution of resistance among the progeny clones. The presented distributions of resistance scores indicate quantitative nature of resistance to G. pallida. Furthermore, this resistance is specific to each pathotype and may be controlled by different genes. We also conclude that there is a need for independent evaluation of resistance for both pathotypes of G. pallida (Pa2 and Pa3).

South American species <i>Solanum alandiae</i> Card. and <i>S. okadae</i> Hawkes et Hjerting as potential sources of genes for potato late blight resistance

For several decades, wild species of Solanum L. section Petota Dumort. have been involved in potato cultivar breeding for robust resistance to pests and diseases. Potato late blight (LB) is caused by oomycete Phytophthora infestans (Mont.) de Bary, and the genes for race-specific resistance to P. infestans (Rpi genes) have been introgressed into cultivated potatoes by remote crosses and trans- or cisgenesis, first from S. demissum Buk. and, more recently, from other wild species, such as S. bulbocastanum Dun., S. stoloniferum Schlechtd. et Bché, and S. venturii Hawkes et Hjerting (according to the nomenclature by Hawkes, 1990). Most wild species already involved in breeding for LB resistance came from North and Central Americas: series Bulbocastana (Rydb.) Hawkes, Demissa Buk. and Longipedicellata Buk., and some Rpi genes of these species have been already characterized in much detail. Rpi genes of South American species, including the series Tuberosa (Rydb.) Hawkes, have not been sufficiently investigated. Among the latter, this study focuses on the Rpi genes of S. alandiae Card. and S. okadae Hawkes et Hjerting. Four accessions of S. alandiae, one accession of S. okadae and 11 clones of interspecific potato hybrids comprising S. alandiae germplasm from the VIR collection were PCR-screened using specific SCAR (Sequence Characterized Amplified Region) markers for eight Rpi genes. SCAR amplicons of five Rpi genes registered in this study were validated by comparing their sequences with those of prototype genes deposited in the NCBI Genbank. Among the structural homologues of Rpi genes found in S. alandiae and S. okadae, of special interest are homologues of CC-NB-LRR resistance genes with broad specificity towards P. infestans races, in particular R2=Rpi-blb3, R8, R9a, Rpi-vnt1 and Rpi-blb2 (94–99, 94–99, 86–89, 92–98 and 91% identity with the prototype genes, respectively). Our data may help to better understand the process of Rpi gene divergence along with the evolution of tuberbearing Solanum species, particularly in the series Tuberosa.

Characterizing Colonization Patterns of Clavibacter michiganensis During Infection of Tolerant Wild Solanum Species.

Clavibacter michiganensis is the Gram-positive causal agent of bacterial canker of tomato, an economically devastating disease with a worldwide distribution. C. michiganensis colonizes the xylem, leading to unilateral wilt, stem canker, and plant death. C. michiganensis can also infect developing tomato fruit through splash dispersal, forming exterior bird's eye lesions. There are no documented sources of qualitative resistance in Solanum spp.; however, quantitative trait loci conferring tolerance in Solanum arcanum and Solanum habrochaites have been identified. Mechanisms of tolerance and C. michiganensis colonization patterns in wild tomato species remain poorly understood. This study describes differences in symptom development and colonization patterns of the wild type (WT) and a hypervirulent bacterial expansin knockout (ΔCmEXLX2) in wild and cultivated tomato genotypes. Overall, WT and ΔCmEXLX2 cause less severe symptoms in wild tomato species and are impeded in spread and colonization of the vascular system. Laser scanning confocal microscopy and scanning electron microscopy were used to observe preferential colonization of protoxylem vessels and reduced intravascular spread in wild tomatoes. Differences in C. michiganensis in vitro growth and aggregation were determined in xylem sap, which may suggest that responses to pathogen colonization are occurring, leading to reduced colonization density in wild tomato species. Finally, wild tomato fruit was determined to be susceptible to C. michiganensis through in vivo inoculations and assessing lesion numbers and size. Fruit symptom severity was in some cases unrelated to severity of symptoms during vascular infection, suggesting different mechanisms for colonization of different tissues.

The presence of Phytophthora infestans in the rhizosphere of a wild Solanum species may contribute to off-season survival and pathogenicity

We evaluated oomycete presence and abundance in the rhizosphere of wild perennial Solanum species to investigate the presence of plant pathogenic or mycoparasitic species. Furthermore, we investigated whether these plant species could function as hosts, or associated plants, for off-season survival of economically important pathogens. We collected soil samples in Sweden from Solanum dulcamara and as a control from Vitis vinifera over all four seasons of a year, and in New Zealand from Solanum nigrum and Solanum laciniatum in the summer. Species identification, confirmed by ITS and Cox2 sequencing, and root infection assays on the crop plant Solanum tuberosum and on S. dulcamara, suggested the presence of mainly Pythiales species. In Sweden, we also found evidence for the presence of Phytophthora infestans, the causal agent of potato late blight, in the rhizosphere of S. dulcamara. These Ph. infestans isolates had no negative effects on root growth of S. dulcamara in Sweden, but were more pathogenic on potato leaves than a common lab strain. Oomycete diversity measures indicated a high similarity between seasons and countries. In conclusion, our study suggests a previously unknown overwintering strategy for the pathogen Ph. infestans, indicating a possible influence of the wild species S. dulcamara on the epidemiology of potato late blight in Sweden.

Polymorphisms and Evolution of Solanum bulbocastanum Genes for Broad-Spectrum Resistance to Phytophthora infestans

For two decades, Solanum bulbocastanum Dun. has been challenging potato geneticists with its durable resistance to Phytophthora infestans Mont. de Bary, the causal agent of late blight, the most devastating potato disease. In this study, highly specific SCAR (sequence characterized amplified region) markers for three S. bulbocastanum genes of broad-spectrum resistance to P. infestans,RB/Rpi-blb1,Rpi-blb2 and Rpi-blb3, were employed to screen a vast collection of wild tuber-bearing species from several series of Solanum L. section Petota Dumort. and also potato hybrids and varieties. In S. bulbocastanum and S. stoloniferum Schlechtd. et Bche, the sequences of the markers Rpi-blb1-820 and Rpi-sto1-890, which recognize the LRR and CC regions respectively differed inconsiderably in the orthologous genes RB/Rpi-blb1 and Rpi-sto1. These two markers were tightly linked in diverse wild Solanum genotypes. These markers as well as RB-226, another marker recognizing the LRR region of the Rpi-blb1 gene, were obviously related to high resistance to P. infestans. One more marker recognizing the CC region of the gene, RB-629, was found in much wider range of Solanum genotypes; it was not related to resistance to P. infestans and is therefore considered non-specific. In addition to Rpi-blb1 = Rpi-sto1, the Rpi-blb2 and Rpi-blb3 genes were registered in both S. bulbocastanum and S. stoloniferum accessions. In most cases, three bulbocastanum genes were not linked together. The markers specific for Rpi-blb1 = Rpi-sto1 genes were found in the Solanum series Bulbocastana (Rydb.) Hawkes (genome designation BB) and Longipedicellata Buk. (genome designation AABB) and were absent from five Pinnatisecta Rydb. species also comprising genome B. The marker for Rpi-blb2 was found in the series Bulbocastana and Longipedicellata and also in three accessions of Pinnatisecta, while the Rpi-blb3 gene, the orthologue of widely spread R2 gene for resistance to P. infestans, was present in all three Solanum series. In contrast with Rpi-blb1 = Rpi-sto1, two other functional RB homologues, Rpi-bt1 in S. bulbocastanum and RBver in S. verrucosum Schlechtd. (genome AA), apparently diverged earlier in the evolution of tuber-bearing Solanum species. Our evidence on functional Rpi-blb1 = Rpi-sto1 genes in three Petota series substantiates the assumption that the B genome of tetraploid Longipedicellata evolved from diploid Bulbocastana rather than from diploid Pinnatisecta progenitors. Similar to wild Solanum species, the markers Rpi-blb1-820 and Rpi-sto1-890 were tightly linked in advanced potato hybrids and established varieties bred from S. stoloniferum as the conventional source of bulbocastanum genes for late blight resistance, but did not always match the markers for the Rpi-blb2 and Rpi-blb3 genes and the marker for the Rysto gene as an independent indicator of stoloniferum germplasm.

Taxonomic revision and ethno-medicinal practices of wild species of Solanum L. in eastern Uttar Pradesh, India

Solanum L., is a cosmopolitan genus, comprising 1,500 species, about 75 % of family Solanaceae, but in absence of a recent critical assessment these figures may well be too high. Present paper deals with 8 wild species of Solanum viz. S. diphyllum, S. incanum, S. nigrum, S. sisymbriifolium, S. surattense, S. torvum, S. verbascifolium & S. villosum, which are commonly occurring in study area. Beside detailed enumeration, local name, phenology, locality and ethnomedicinal uses are given along with detailed taxonomic descriptions, photo plates and a key to the identification of species are provided for easy identification.

Evaluation of Solanum species and eggplant cultivated varieties for bacterial wilt resistance

Bacterial wilt caused by Ralstonia solanacearum is one of the major diseases in Solanum species including cultivated Eggplant (Solanum melongena L.). Bacterial wilt (BW) disease management in eggplant is difficult due to high survival rate of pathogen in soil and chemical application is not eco-friendly. The best way to avoid bacterial wilt in eggplant is using disease-resistant varieties. However, only a limited number of bacterial wilt resistant varieties are available and, there is a necessity to identify and/or develop new resistant varieties. In the current study, wild Solanum species, and eggplant cultivated varieties were evaluated against Ralstonia solanacearum, and disease incidence was recorded. The cultivated varieties IIHR-108, Pusa Purple Long and Rampur Local were identified as susceptible, whereas, IIHR-7 and CARI-1 were identified as resistant to bacterial wilt. These resistant wild and cultivated varieties can be used as a root-stock in bacterialwilt disease resistant breeding programmes.

Evaluation of Solanum species and eggplant cultivated varieties for bacterial wilt resistance

Bacterial wilt caused by Ralstonia solanacearum is one of the major diseases in Solanum species including cultivated Eggplant (Solanum melongena L.). Bacterial wilt (BW) disease management in eggplant is difficult due to high survival rate of pathogen in soil and chemical application is not eco-friendly. The best way to avoid bacterial wilt in eggplant is using disease-resistant varieties. However, only a limited number of bacterial wilt resistant varieties are available and, there is a necessity to identify and/or develop new resistant varieties. In the current study, wild Solanum species, and eggplant cultivated varieties were evaluated against Ralstonia solanacearum, and disease incidence was recorded. The cultivated varieties IIHR-108, Pusa Purple Long and Rampur Local were identified as susceptible, whereas, IIHR-7 and CARI-1 were identified as resistant to bacterial wilt. These resistant wild and cultivated varieties can be used as a root-stock in bacterialwilt disease resistant breeding programmes.

PCR-based markers developed by comparison of complete chloroplast genome sequences discriminateSolanum chacoensefrom otherSolanumspecies

One of wild diploid Solanum species, Solanum chacoense, is one of the excellent resources for potato breeding because it is resistant to several important pathogens, but the species is not sexually compatible with potato (S. tuberosum) causing the limitation of sexual hybridization between S. tuberosum and S. chacoense. Therefore, diverse traits regarding resistance from the species can be introgressed into potato via somatic hybridization. After cell fusion, the identification of fusion products is crucial with molecular markers. In this study, S. chacoense specific markers were developed by comparing the chloroplast genome (cpDNA) sequence of S. chacoense obtained by NGS (next-generation sequencing) technology with those of five other Solanum species. A full length of the cpDNA sequence is 155,532 bp and its structure is similar to other Solanum species. Phylogenetic analysis resulted that S. chacoense is most closely located with S. commersonii. Sequence alignment with cpDNA sequences of six other Solanum species identified two InDels and 37 SNPs specific sequences in S. chacoense. Based on these InDels and SNPs regions, four markers for distingushing S. chacoense from other Solanum species were developed. These results obtained in this research could help breeders select breeding lines and facilitate breeding using S. chacoense in potato breeding.

Potato mosaic viruses which infect plants of tuber-bearing Solanum spp. growing in the VIR field gene bank

Potato crop is particularly affected by virus diseases, and potato virus Y (PVY) currently considered the most important pathogen distributed worldwide as a diversity of strains. Wild and cultivated tuber-bearing species of the genus Solanum L., stored in the VIR collection, are used as the initial material in creation domestic potato varieties (Solanum tuberosum L.) resistant to virus diseases. The preservation and rational utilization of the potato collection is based on regular phytosanitary monitoring, including quarantine objects, foremost PSTVd (potato spindle tuber viroid). The aim of the work is to examine plants of tuber-bearing Solanum species in the field gene bank of VIR for the presence of PSTVd and PVX (potato virus X), PVS (potato virus S), PVM (potato virus M) and PVY, which are the most common viruses on potatoes in the North-West District of Russia. We examined clonal plants of 137 genotypes representing 31 species of the section Petota of the genus Solanum L. A diagnostic was carried out using ELISA, RT-PCR and indicator plants. No PSTVd was found in the studied plants, but a plural infestation by mosaic viruses was detected, more than half of the tested clones are infected with two or more viruses. In the studied samples, only 17 genotypes (12 %) are not infected by PVX, PVS, PVM and PVY according to the ELISA test. There are statistically significant differences in the virus infestation of Solanum species with different origins, according to Pearson’s chi-squared test. Among the studied genotypes of wild relatives of potatoes, the proportion of those affected by PVY was significantly higher in the South American than in the North American species (χ2 = 4.56, p = 0.03); the proportion of genotypes affected by PVХ was significantly higher in the North American species (χ2 = 8.81, p = 0.003), the critical value was χ2 = 3.841. PVY strains were identified by multiplex RT-PCR in 37 genotypes of Solanum spp. We found that 27 genotypes are infected by a common PVYO strain, two genotypes are infected by PVYNW (A) and PVYNW (B) strains, respectively, seven genotypes are infected by a mixture of PVYO +PVYNW (A) strains, and one is infected by a mixture of PVYO +PVYNTN-NW (SYRI)+SYRIII strains. The recombinant strains of PVY are detected in the North-West District of Russia for the first time. Coherency of the results of PVY strains detection by various (immunological, molecular and biological) methods is discussed.

A rapid method to screen wild Solanum for resistance to early blight

Early blight of potato and tomato is caused by Alternaria fungi and negatively impacts crop yields. Environmental factors and plant maturity influence disease development, which is usually kept under control by fungicide applications. Wild tuber-bearing Solanum section Petota species are a promising source of resistance to early blight that could be used to control the disease, for example by crossbreeding or modern breeding approaches. An efficient screening method is a first prerequisite for the identification of resistant genotypes in wild Solanum germplasm. Here, we describe a protocol that can be used to rapidly screen for resistance to early blight in wild Solanum collections. This protocol provides a good starting point for the identification of resistant genotypes and is a step towards breeding for resistance to early blight using wild Solanum species.

Heat Tolerance in Diploid Wild Potato Species In Vitro

Potatoes are a cool season crop. Yet, with growth in the world population and rising temperatures, more heat tolerant cultivars are going to be needed. The objectives of this work were to identify heat tolerance in diploid wild Solanum species, as measured by the ability to form microtubers in tissue culture, and to compare four different methods of evaluating heat tolerance. In each of five experiments conducted over time, four nodal cuttings from up to 20 genotypes from each of ten diploid wild potato species were grown in MS medium supplemented with 8% sucrose and cultured at 19 °C (cool) and 25 °C (warm) in the dark. Four methods were used to evaluate heat tolerance: percent microtuberization under warm conditions, difference in percent microtuberization between cool and warm conditions, microtuber yield under warm conditions, and the difference in microtuber yield between cool and warm conditions. Species were ranked for each of these four methods (with rank = 1 being most heat tolerant) and ranks were summed across the four methods to identify the most heat tolerant. There were significant differences among species and the species x temperature interaction was significant for percent microtuberization and microtuber yield. Percent microtuberization in five of the species was similar under cool and warm temperatures; greater under cool temperatures for three species; and, greater under warm temperatures for two species. Microtuber yield in four of the species was similar under cool and warm temperatures; greater under cool temperatures for six species; and, greater under warm temperatures for one species. Rankings of heat tolerance among the species varied by the method used, but S. kurtzianum and S. sogarandinum were the most heat tolerant.

Development of PCR-based markers for discriminating Solanum berthaultii using its complete chloroplast genome sequence

Solanum berthaultii is one of the wild diploid Solanum species, which is an excellent resource in potato breeding owing to its resistance to several important pathogens. On the other hand, sexual hybridization between S. berthaultii and S. tuberosum (potato) is limited because of their sexual incompatibility. Therefore, cell fusion can be used to introgress various novel traits from this wild species into the cultivated potatoes. After cell fusion, it is crucial to identify fusion products with the aid of molecular markers. In this study, the chloroplast genome sequence of S. berthaultii obtained by next-generation sequencing technology was described and compared with those of five other Solanum species to develop S. berthaultii specific markers. A total sequence length of the chloroplast genome is 155,533 bp. The structural organization of the chloroplast genome is similar to those of the five other Solanum species. Phylogenic analysis with 25 other Solanaceae species revealed that S. berthaultii is most closely located with S. tuberosum. Additional comparison of the chloroplast genome sequence with those of the five Solanum species revealed 25 SNPs specific to S. berthaultii. Based on these SNPs, six PCR-based markers for differentiating S. berthaultii from other Solanum species were developed. These markers will facilitate the selection of fusion products and accelerate potato breeding using S. berthaultii.

RESULTS OF NEW TRENDS OF POTATO BREEDING PROGRAMS DEVELOPED IN RUSSSIA

The article presents the results of introgression of valuable genes from wild and cultivated species of Solanum and varieties of the world collection (CIP) to selection varieties in the production of backcross hybrids, selection of recombinants in backcross generations and in offspring from crossbred crosses among themselves, as well as special parent lines for implementation of programs in various areas of potato breeding. Studies were conducted to determine the effectiveness of different types of crossing during backcrossing in the frequency of occurrence of recombinant forms with high rates of polygenic traits in the hybrid progeny. Hybrids-backcrosses for immunity to virus Y, field resistance to late blight and resistance to the pathogen Ro1 of the golden potato nematode were evaluated by the method of artificial infection in pot-plant in a greenhouse. Analysis of hybrid progeny for starch content and suitability for processing by the color of chips was carried out under laboratory conditions. According to the results of the analysis of the pedigrees of 10 varieties of potato originating from the two forms of S. chacoense, a high efficiency of recurrent accumulation crosses providing introgression of the dominant immunity genes to the virus Y is revealed, as well as resistance to alternaria, heat and drought. Medium-late varieties with high field resistance of leaves and tubers were created on the basis of unstable to the late blight hybrid (F1 S. chacoense 55 d x Agra) and 3 recurrent crosses. In this case, varieties with medium field resistance to late blight participated in backcrossing. When assessing the collection of wild species for resistance to the pathogen Ro1 of the golden potato nematode, only one new source of S. chacoense 58 d was detected. Analysis of the cleavage in resistance to nematode among populations from the crossing of three-species hybrids (vrn x chc) x tbr and backcross hybrids (vrn x chc) x tbr2 confirmed control of the trait by one dominant gene, which facilitates selection for this feature. Based on the analysis of the frequency of occurrence of hybrids with different starch content in the fissile offspring, it is established that this feature is controlled by a small amount of pure additively acting genes. In the hybrid populations studied, the symmetrical frequency distribution, the presence of transgressions, and the high correlation between the average starch content of parental forms and the average offspring were observed. In a comparative assessment of 36 hybrid populations on the suitability for processing for potato products, methods for selecting parental forms for crossing and timing of the evaluation of the trait in different periods of tuber storage have been identified. Twenty-two hybrids are identified that are suitable for processing during the entire storage period without reconditioning. An increase in the efficiency of the selection process was noted in the repeated use of identical hybrid populations for selection in various environmental and geographical conditions, which significantly reduces the financial costs of creating a variety.

The atroviolacea Gene Encodes an R3-MYB Protein Repressing Anthocyanin Synthesis in Tomato Plants.

The anthocyanin biosynthetic pathway is well characterized in plants. However, in tomato (Solanum lycopersicum L.) an exhaustive knowledge of its regulation is still lacking. Tomato mutants showing higher levels of anthocyanins in fruits or vegetative tissues, such as Anthocyanin fruit (Aft) or atroviolacea (atv), have been extensively exploited in the attempt to clarify the process. Nevertheless, only candidate genes have been proposed as responsible for such phenotypes. The recessive atv mutation likely represents an allelic variant of a gene introgressed in tomato from wild Solanum species. We performed genome sequencing of atv/atv plants followed by candidate gene analysis, and identified a mutated gene encoding an R3-MYB protein. When overexpressed, this protein abolished anthocyanin production in tomato seedlings and plants, by silencing key regulators and biosynthetic genes of the pathway. The functional analysis of the protein clearly showed that it can negatively interfere with the activation of the anthocyanin biosynthetic pathway mediated by the endogenous MYB-bHLH-WDR (MBW) complexes. In particular, this R3-MYB protein can directly bind the bHLH factors which are part of the MBW complexes, therefore acting as a competitive inhibitor. The R3-MYB protein here described is therefore involved in a feedback mechanism that dampens the production of anthocyanins once activated by endogenous or exogenous stimuli. The atv mutation causes the production of a truncated version of the R3-MYB factor that cannot retain the full potential to inhibit the MBW complexes, thus leading to a constitutively higher production of anthocyanins.

Identification of Mi-1 homologs in various Solanum species

In Ecuador, several solanaceous crops, including naranjilla (Solanum quitoense), are attacked by the nematode Meloidogyne sp. Resistant cultivars are not available and there is a need to identify potential sources of resistance that can be incorporated into breeding programs. The Mi-1 gene from S. peruvianum is known to confer resistance to Meloidogyne in tomato (S. lycopersicum).
 In this study, 42 plant accessions of wild and cultivated Solanum species were screened to identify the presence of this gene, its diversification, expression, and evidence of gene recombination. The Mi-1 gene (exon 3) was identified in 34 accessions. Sixteen alleles were identified, that encode 15 different amino acid sequences, all of which encode NBS-LRR proteins and share 72-96 % homology with the tomato Mi-1 protein. The Mi-1 locus was highly polymorphic; most polymorphisms tend to accumulate in the NBS rather than in the LRR region. Genetic recombination was detected among the tomato and potato relate d sequences, but it was absent in the naranjilla group. Homologs identified expressed in both non-infected roots and leaves of some accessions, suggesting the constitutive expression of the gene.

Reaction of wild eggplant Solanum torvum to different species of root-knot nematodes from Turkey

The cultivated eggplant species are susceptible to root-knot nematodes (Meloidogyne spp.). However, many wild Solanum species, such as S. torvum, S. sisymbriifolium, S. aethiopicum and S. warscewiczii, are resistant to some root-knot nematodes. Only S. torvum is employed as a rootstock for eggplant cultivation worldwide. This study investigated the response of S. torvum cv. Hawk against the root-knot nematodes Meloidogyne incognita, Mi-1 virulent M. incognita, M. javanica, M. arenaria and M. luci and M. hapla from Turkey, under controlled conditions. A local eggplant cultivar and a commercial eggplant hybrid were included in the bioassay. Eggplant seedlings were each inoculated with 1000 second-stage juveniles of Meloidogyne spp. and uprooted 8 weeks after nematode inoculation. Then, egg masses and galls on the roots were counted. S. torvum was resistant to M. incognita, Mi-1 virulent M. incognita, M. javanica, M. arenaria and M. luci, but susceptible to M. hapla. In Turkey, S. torvum has commonly been used as a rootstock against Meloidogyne spp. The study provided background information of S. torvum rootstock resistance to the mentioned populations of root-knot nematodes, except M. hapla.