Wild Solanum Species Research Articles

Advantages of Wild Diploid Solanum Species Over Cultivated Diploid Relatives in Potato Breeding Programs

For breeding programs of the tetraploid potato (Solanum tuberosum), both wild and cultivated diploid relatives are valuable sources of genetic diversity. While both types of germplasm are used in breeding programs, there are several advantages to using wild relatives. Diploid relatives are typically crossed with haploids (2n = 2x = 24) from tetraploid S. tuberosum to improve daylength adaptation. Most haploids are male sterile, so they are typically used as female parents. Cultivated diploids, such as members of the Phureja Group, produce male sterile hybrids when crossed as females to haploids; wild relatives, such as S. tarijense, often produce male fertile hybrids. Tuber yield following crosses of haploids to cultivated or wild relatives is often high. However, cultivated relatives generally produce hybrids with a high set of small tubers; hybrids from wild relatives are variable, but many are similar to cultivars in tuber size and set. While tubers of hybrids from cultivated relatives are typically rough, with deep eyes and raised internodes, those from wild relatives are often smooth. Tuber dormancy in hybrids with cultivated relatives is generally short, while that in hybrids with wild species is longer, allowing for storage over winter. Finally, resistance to several major diseases and stresses has been found in wild species and their hybrids with S. tuberosum haploids. The desirable traits in hybrids are transmitted to tetraploids via unilateral sexual polyploidization (4x × 2x or 2x × 4x crosses in which the diploid parent produces 2n gametes). Wild Solanum species are recommended for use in potato breeding programs as sources of genetic diversity that can be adapted easily following hybridization with S. tuberosum haploids.

Influence of Incorporated Wild Solanum Genomes on Potato Properties in Terms of Starch Nanostructure and Glycoalkaloid Content

Interspecific somatic hybrids produced by protoplast fusion between two wild Solanum species (S. acaule, acl; S. brevidens, brd) and cultivated potato Solanum tuberosum (tbr) were analyzed in terms of the starch nanometer-range structure and glycoalkaloid (GA) contents. The crystallinity of starch granules, the average size of starch crystallites, and the lamellar distances were obtained from tuber samples using wide-angle and small-angle X-ray scattering methods. These measurements showed that incorporation of wild genomes from either nontuberous (brd) or tuberous (acl) Solanum species caused no significant modifications of the nanostructure of potato starch. In contrast, the GA profiles of the hybrids, which were analyzed by LC-ESI-MS in both tuber and foliage samples, differed considerably from those of cultivated potato. Regardless of the low total tuber GA concentrations (approximately 9 mg/100 g of fresh weight), the somatic hybrids contained GAs not detected in the parental species. A high proportion of spirotype GAs consisting of 5,6-dihydrogenated aglycons, for example, alpha-tomatine and tomatidine bound with solatriose, and chacotriose were found in the hybrids. In conclusion, the foliage of interspecific hybrids contained a higher variation in the structures of GAs than did the tubers.

Eggplant (Solanum melongena L.): tissue culture, genetic transformation and use as an alternative model plant

Eggplant is an agronomically important non-tuberous solanaceous crop grown primarily for its large oval fruit. In popular medicine, eggplant is indicated for the treatment of several diseases, including diabetes, arthritis, asthma and bronchitis. Eggplant is susceptible to a number of diseases and pests capable of causing serious crop losses. This problem has been addressed by hybridizing eggplant with wild resistant Solanum species, which present a wide genetic diversity and are source of useful agronomic traits. The application of in vitro methodologies to eggplant has resulted in considerable success. Eggplant tissues present a high morphogenetic potential that is useful for developmental studies as well as for establishing biotechnological approaches to produce improved varieties, such as embryo rescue, in vitro selection, somatic hybridization and genetic transformation. Taken together, these characteristics also make eggplant a complete model for studies on different areas of plant science, including control of gene expression and assessment of genetic stability of somaclones derived from different morphogenetic processes. In the present study, important factors that affect the efficiency of in vitro regeneration through organogenesis and embryogenesis as well as genetic transformation are analyzed. The potential of this species as a model plant for studying various aspects of plant genetics and physiology is also discussed.

Foreign exploration for natural enemies of the Colorado potato beetle in Central and South America

Abstract To expand the area searched for natural enemies of the Colorado potato beetle, Leptinotarsa decemlineata (Say) we collected throughout Honduras, Guatemala, and El Salvador and also made collecting trips to Colombia, Bolivia, and Ecuador. In South America the only Leptinotarsa beetles encountered were L. undecimlineata (Say) collected in Colombia, where few natural enemies were found. In Central America, L. undecimlineata Stal was again the only Leptinotarsa collected, and this species was found commonly on several wild Solanum species. Among natural enemies collected from L. undecimlineata were several species of tachinid parasitoids (Myiopharus spp.), the egg parasitoid Edovum puttleri Grissell, and several hyperparasitic species (Exoristobia sp., Perilampus sp., and Conura n. sp.). Only one pathogen, the microsporidium Endoreticulatus fidelis (Hostounsky and Weiser) was found. Predators included a number of generalists, primarily of the egg, and early larval stages. The ectoparasitic mite, Chrysomelobia spp., was also observed under the elytra of infested beetles. Although many of the natural enemies had been discovered previously, options for importation biological control of L. decemlineata could be improved by a better understanding of the taxonomy of existing groups, determination of the specificity of the beetle’s hyperparasitoids and predators, and further study of the impact of ectoparasitic mites and natural enemies attacking the pupal stage. Finally, the spatial and temporal occurrence of Leptinotarsa on their host plants suggest meta-population effects that could serve as selective forces influencing the densities and diversity of beetle natural enemies.

Investigation of resistance specificity amongst fifteen wild Solanum species to a range of Globodera pallida and G. rostochiensis populations

AbstractThe breadth of resistance to populations of the potato cyst nematodes, Globodera pallida and G. rostochiensis, which differed both in virulence level and country of origin, was investigated in 15 wild Solanum species. A range of responses to the populations was noted, with significant interactions observed between the potato genotypes and Globodera populations assayed. Of the 15 wild Solanum species, seven appeared to be potentially valuable sources of wide spectrum resistance with low multiplication rates with all populations recorded. The inclusion of these species into a potato breeding programme is justified by this study.

Life stage responses observed amongst fifteen wild Solanum species resistant to Globodera pallida

AbstractThe resistance responses present in 15 wild Solanum species to the potato cyst nematode Globodera pallida were investigated, focusing on hatch, invasion, development, sex determination and fecundity. A wide range of resistance responses was observed among the species, which impacted at different points in the life cycle of G. pallida. For most species a reduced rate of development and subsequent shifts towards an increased male to female ratio, indicative of a poor nutritional host, were observed. However, S. acaule ssp. acaule and S. canasense appeared to possess unique resistance responses, and may comprise valuable sources of new genes for incorporation into potato breeding programmes.

Influence of near null magnetic field on in vitro growth of potato and wildSolanum species

The influence of near null magnetic field on in vitro growth of different cultures of potato and related Solanum species was investigated for various exposure times and dates. Potato (Solanum tuberosum L. cv. Désirée) in vitro cultures of shoot tips or nodal segments were used. Three different exposure periods revealed either stimulation or inhibition of root, stem, or leaf in vitro growth after 14 or 28 days of exposure. In one experiment the significant stimulation of leaf growth was also demonstrated at biochemical level, the quantity of chlorophyll a and b and carotenoids increasing more than two-fold. For the wild species Solanum chacoense, S. microdontum, and S. verrucosum, standardized in vitro cultures of nodal stem segments were used. Root and stem growth was either stimulated or slightly inhibited after 9 days exposure to near null magnetic field. Callus cultures obtained from potato dihaploid line 120/19 were maintained in near null magnetic field in 2 different months. For these experiments as well as for Solanum verrucosum, callus cultures recorded either slight inhibition or no effect on fresh weight. For all experiments significant growth variation was brought about only when geomagnetic activity (AP index) showed variations at the beginning of in vitro growth and when the explant had at least one meristematic tissue. Moreover longer maintenance in near null magnetic field, 28 days as compared to 14 days or the controls, can also make a difference in plant growth in response to geomagnetic field variations when static component was reduced to zero value. These results of in vitro plant growth stimulation by variable component of geomagnetic field also sustain the so-called seasonal "window" effect.

Evaluation ofSolarium fendleri as a source of resistance toMeloidogyne chitwoodi

Twelve accessions ofSolarium fendleri collected in the United States and Mexico were inoculated with 5,000 eggs of host-races 1 and 2 ofMeloidogyne chitwoodi, Columbia root-knot nematode. The test seedlings that were derived from plant introduction true seed lots were maintained for 55 days before harvest and egg count. The results revealed that two accessions, PI 275162 and PI 275165, were non-hosts (final egg count/initial egg inoculation < 0.1) forM. chitwoodi race 1. The results were uniformly confirmed in the second experiment. No resistance was found to race 2. The tetraploidS. fendleri accessions were crossed to a nematode-susceptible cultivated diploid potato clone from aS. phurejastenotomum population. The triploid hybrids expressed resistance to race 1 at the non-host level. After somatic doubling, the resulting hexaploids also expressed non-host-level resistance to race 1. The two resistant accessions had been collected in southeastern Arizona, one each from the Huachuca and Chiricahua Mountains. Each range is an isolated island of high-elevation mesic flora surrounded by typical lowerelevation Sonora-type desert habitat. These accessions are the only known sources of resistance toM. chitwoodi from wildSolanum species in the USA.

Use of reciprocal grafts to elucidate mode of resistance to Colorado potato beetle (Leptinotarsa decemlineata (Say)) and potato aphid (Macrosiphum euphorbiae (Thomas)) in six wildSolanum species

Reciprocal grafts were done between potato (Solanum tuberosum) and six wildSolanum species known to be resistant to the Colorado potato beetle (Leptinotarsa decemlineata (Say)). Potato or wildSolanum foliage from each reciprocal graft was fed to first instar beetles or adult potato aphids (Macrosiphum euphorbiae (Thomas)). The proportion of second instar larvae after 48 h and survival and fecundity (number of nymphs per female) of the aphids were used to i estimate the resistance level of the foliage. Survival and fecundity of potato aphid were reduced on wildSolanum foliage (except withS. circaeifolium ssp.capsicibaccatum andS. okadae) used as scion or rootstock, but were not different from the control (potato-potato graft) on potato foliage. Development of Colorado potato beetle onSolanum foliage was reduced. In some cases, potato foliage grafted to wildSolanum became resistant to the beetle. Results suggest that a chemical factor or factors providing resistance to Colorado potato beetle are translocated from foliage of some wildSolanum species to potato foliage. They also indicate that mode of resistance to the two insects differs quantitatively or qualitatively.

Solanaceae — a model for linking genomics with biodiversity

Recent progress in understanding the phylogeny of the economically important plant family Solanaceae makes this an ideal time to develop models for linking the new data on plant genomics with the huge diversity of naturally occurring species in the family. Phylogenetics provides the framework with which to investigate these linkages but, critically, good species-level descriptive resources for the Solanaceae community are currently missing. Phylogeny in the family as a whole is briefly reviewed, and the new NSF Planetary Biodiversity Inventories project ‘PBI: Solanum—a worldwide treatment’ is described. The aims of this project are to provide species-level information across the global scope of the genus Solanum and to make this available over the Internet. The project is in its infancy, but will make available nomenclatural information, descriptions, keys and illustrative material for all of the approximately 1500 species of Solanum. With this project, the opportunity of linking valid, up-to-date taxonomic information about wild species of Solanum with the genomic information being generated about the economically important species of the genus (potato, tomato and eggplant) can be realized. The phylogenetic framework in which the PBI project is set is also of enormous potential benefit to other workers on Solanum. The community of biologists working with Solanaceae has a unique opportunity to effectively link genomics and taxonomy for better understanding of this important family, taking plant biology to a new level for the next century.

Resistance toFusarium sambucinum in wild and cultivatedSolanum species

Several species ofFusarium cause both dry rot in storage and seedpiece decay in the field, which results in severe losses in all major potato-growing regions. In temperate climates twoFusarium species are the principle causes of tuber dry rot-F.sambucinum andF. coeruleum. Resistance toF. sambucinum was identified in cultivated and wildSolanum species. Relatively high levels of resistance exist in the following 2EBN species:S. boliviense (PI#’s 265860, 310975, 310974, 545853, 545889, 545964),S. gourlayi ssp.gourlayi (PI#’s 473344, 545865),S. microdontum (PI#’s 310979, 473171),S. sancta-rosae (PI# 498392),S. kurtzianum (PI# 472930),S. fendleri ssp.fendleri (PI# 262895),S. gandarillasii (PI#’s 265866, 283076),S. oplocense (PI# 498281) andS. vidaurrei (PI# 498332). The resistance is highly heritable but appears, at least in some of the species, to be associated with recessive alleles.

Resistance to Phytophthora infestans in somatic hybrids of Solanum nigrum L. and diploid potato.

In breeding for resistance to late blight, ( Phytophthora infestans Mont. de Bary), an economically important disease affecting potatoes, the search for new sources of durable resistance includes the non-host wild Solanum species. The aim of this work was to evaluate the resistance to P. infestans in the somatic hybrids between S. nigrum L. and diploid potato clone ZEL-1136. Sixteen somatic hybrids, their fusion parents, and three standard potato cultivars were screened for resistance to P. infestans in two types of tests-on whole plants and detached leaves-with two highly aggressive and virulent isolates of P. infestans, US8 and MP322. In the whole plant assay, the foliage of the somatic hybrids showed no symptoms of infection, while the foliage of the potato fusion parent and the standard cultivars was infected with P. infestans. In the detached leaflet assay, the breaking-down of resistance of the S. nigrum L. parent and the variable response of individual hybrid clones were noted. Nine S. nigrum L. (+) ZEL-1136 hybrids showed a resistance that was significantly higher than that of S. nigrum, while six clones expressed a resistance to P. infestans similar to that of S. nigrum. The results confirm the effective transfer of late blight resistance of S. nigrum into its somatic hybrids with potato.

Multiple Disease Resistance in Interspecific Hybrids of Potato.

Wild species of Solanum are excellent sources of disease resistance genes that may be incorporated into S. tuberosum through breeding. This study was initiated to determine whether multiple forms of disease resistance could be identified in interspecific Solanum hybrids. Thirty-two clones were evaluated for resistance to soft rot, common scab, black scurf, Verticillium wilt, and early blight. Most of the clones originated from populations that were not initially selected for disease resistance traits. Comparisons with the cultivars Atlantic, Russet Norkotah, and Russet Burbank indicated that all clones were more resistant than at least one cultivar for at least one disease resistance trait. Clone C545, which exhibited improved resistance to soft rot, scab, pitted scab, early dying disease, and early blight, appears to be an especially valuable source of disease resistance. The use of interspecific hybridization at the diploid level, combined with sexual polyploidization to return to the tetraploid level, provides a method to introduce multiple forms of disease resistance into advanced clones.

Resistance to late blight and soft rot in six potato progenies and glycoalkaloid contents in the tubers

Glycoalkaloids are anti-nutritional compounds commonly found in wildSolanum species used as resistance sources to major potato pathogens. It is therefore important for breeding purposes to know whether selecting for resistance using such species necessarily selects also for high glycoalkaloid contents in the tubers. To test this hypothesis, we used six partial progenies from crosses betweenSolanum tuberosum and accessions ofS. andigena, S. berthaultii, S. phureja, andS. vernei to investigate the possible correlation between resistance toPhytophthora infestans and/or toErwinia carotovora subsp.atroseptica and the concentration of glycoalkaloids in tubers. Concentrations of α-solanine and α-chaconine in the tubers segregated in each progeny, as did resistance to each pathogen. Some, but not all, clones from each progeny showed hypersensitive reactions to the isolate ofP. infestans used. Furthermore, clones within each progeny also differed for components of partial resistance toP. infestans, suggesting that all four wild species could be used as sources of both race-specific and partial resistance to late blight. With the exception of low, but statistically significant, correlations between concentration of α-solanine and two late blight resistance components (incubation period and spore production per unit lesion area) in progenies derived fromS. vernei, and despite a trend towards higher glycoalkaloid concentrations in the tubers of the clones most resistant to soft rot within progenies derived fromS. berthaultii andS. vernei, no consistent relationship between resistance to either disease and concentrations of α-solanine and/or α-chaconine was observed. These results indicate that neither race-specific nor partial resistance to late blight and soft rot in the accessions used as progenitors of resistance depend on high solanine or chaconine concentrations. These resistance sources could thus prove useful in breeding programs for improved behaviour againstP. infestans and/orE. carotovora.

Crossability relationships among the wild diploid potato species Solanum kurtzianum, S. chacoense and S. ruiz-lealii from Argentina

The wild tuber-bearing Solanumspecies represent a genetic pool of enormous diversity, embracing high variability for many agronomic traits. S. kurtzianum (ktz), S. chacoense(chc) and S. ruiz-lealii (rzl) are wild diploid self-incompatible relatives of the common potato, Solanum tuberosumssp. tuberosum, with resistance to adverse biotic and abiotic factors. Pollen-pistil/style compatibility relations and seed set in intra- and interspecific crosses among ktz, chc and rzl were investigated. Pre- and post-zygotic hybridization barriers were detected in the three species, with variable incidence because the percentage of genotypic combinations that produced seeds was15–30% and 7–28% in intra and interspecific crosses, respectively. In pollen-pistil/style incompatible combinations, either pollen grains did not germinate or pollen tube growth was arrested at different sites of the style, but mainly in its upper third. Unilateral incompatibility was detected in both intra-and interspecific crosses, as well as bilateral incompatibility in certain combinations. The incompatibility relations observed could be explained by a genetic model with dominant genes in pistils that interact with corresponding dominant genes in pollen, that are independent of the S-locus. The complex arrangement of compatibility relationships found could not be directly related to taxonomic hypothesis or geographic distribution. These results suggest that divergence between the three species has occurred recently, and that internal barriers of reproductive isolation have not been an important factor in their evolution.

Comparison of gene expression in Solanum bulbocastanum infected with virulent and avirulent isolates of Meloidogyne chitwoodi

Resistance to root knot nematode M. chitwoodi has been identified in the wild tuber-bearing Solanum species, S. bulbocastanum. Three pathotypes were identified suggesting at least two different genetic factors for virulence and resistance in the pathogen and the host species, respectively. Roots of S. bulbocastanum were infested with two isolates of M. chitwoodi differing in virulence. The infection process was monitored by histological examination of roots allowing time points to be identified. cDNA libraries were constructed from infected root tissue using Suppression Subtractive Hybridisation (SSH) to enrich for transcripts from either compatible or incompatible interactions, at three days and seven days post infection. Both plant and nematode genes, which may be important during the host/parasite interaction, were identified.

Grafting Compatibility of Cultivated Eggplant Varieties with Wild Solanum Species

Grafting Compatibility of Cultivated Eggplant Varieties with Wild Solanum Species

An analysis of the hybrid nature ofsolanum xedinense Berth, using molecular, cytological and crossability studies

Solanum xedinense Berth., a pentaploid (2n=5x=60) interspecific hybrid between the cultivated potato and the wild speciesSolanum demissum Lindl., represents evidence of genetic exchange between wild and cultivated species. It has been found in Central Mexico at altitudes between 2000 and 3500 meters, growing in and along the edges of cultivated fields, roadside thickets, forest margins and along irrigation ditches. This study examined the hybrid nature of S.xedinense using molecular, cytological and crossability data. RAPD and AFLP markers were used to supportS. xedinense as a hybrid between the cultivated potato andS. demissum. Meiotic analysis and crossability studies were used to examine the potential ofS. xedinense to form offspring. Several accessions ofS. tuberosum L. subsp.tuberosum and subsp.andigena Hawkes,S. demissum and an accession ofS. xedinense were used in the study. Artificial hybrids betweenS. tuberosum subsp.tuberosum andS. demissum were included for comparison. Molecular analysis positioned the natural and artificial hybrids as an intermediate group between the parental populations, supporting their relationship with the parental populations. Meiosis was abnormal in both natural and artificial hybrids, and reduced crossability was noted forS. xedinense. Although gene flow appears to happen between wild and cultivated potato, the potential for the natural hybrids to become established may depend mostly on their ability to clonally propagate themselves.

Molecular evolution of 5S rDNA of Solanum species (sect. Petota): application for molecular phylogeny and breeding

Nucleotide sequences of 5S rRNA genes (5S rDNA) of 26 wild species of the genus Solanum (sect. Petota) originating from Middle or South America, four Solanum tuberosum breeding lines and one European species, Solanum dulcamara (sect. Dulcamara) were compared with each other and with the 5S rDNA of Lycopersicon esculentum. The length of the repeat ranges from 285 bp to 349 bp. The complete 5S repeat unit consists of the 120-bp long conserved coding region and of a intergenic spacer with a high variability in the central portion as result of deletions/duplications of short motifs demonstrating sequence similarity to box C in the 5S rRNA coding region. Numerous structural rearrangements found in the spacer region can be applied to design species-specific molecular markers for Solanum species involved in breeding programs. Characteristic insertions/deletions (indels) were used to reconstruct phylogenetic relationships among the species studied. S. dulcamara forms a separate clade; L. esculentum is more related to Solanum species of sect. Petota. Conservation of ancestral 5S spacer organization was demonstrated for the representatives of several series of sect. Petota, both Stellata and Rotata. Further rearrangements of the spacer organization occurred in at least four independent lineages: (1) L. esculentum, (2) ser. Polyadenia, (3) other Stellata species from Middle America (ser. Pinnatisecta and Bulbocastana), (4) superser. Rotata. In this last group, series Megistacroloba and Conocibaccata show a common origin, and separation from ser. Tuberosa. Solanum chacoense and Solanum maglia demonstrate a close relatedness to species of ser. Tuberosa and should be included into this group, whereas Solanum bukasovii should be excluded due to conservation of ancestral spacer organization. Three major subgroups may be distinguished for species from ser. Tuberosa, although a high sequence similarity was found here. Several wild species (diploids Solanum phureja and Solanum spegazzinii) probably participated in the natural origin of tetraploid S. tuberosum;others were later used for crossing in breeding programs (e.g. Solanum demissum). Clear separation of Middle-American Stellata species from South-American Stellata and from Middle-American Rotata polyploids is shown.

Allozyme polymorphisms in tetraploid potato gene pools and the effect on human selection

The need for broadening a crop’s genetic base may be determined by comparing allele frequencies within the gene pools of farmer selections in their centers of diversity with that of modern breeding populations. The genetic structure of Andean and Chilean potato farmer selections was investigated with the aid of nine isozymes, which have been studied in detail and used to characterize North American cultivars and advanced breeding lines. These isozymes are associated with the most-important agronomic or quality characters in the North American gene pool. By comparing these data with previous analyses of the North American gene pool, allozyme frequency changes for nine loci were monitored. Allozyme frequency changes were not always due to genetic drift, but resulted also from directional selection of isozyme marker linked quantitative trait loci (QTLs) affecting agronomic or quality characters. Changes in allozyme frequency can also occur as a consequence of pleiotropy, i.e. the isozyme itself may be involved in the expression of a phenotype. These allozyme frequency changes may reflect the manipulation of the potato genome by breeders. There were allozymes in some North American cultivars that were not observed in the farmer selections from the Andes and Chile. This confirms that breeders have already introgressed exotic genes from wild and other primitive cultivated tuber-bearing Solanum species. On this basis, the need for broadening the genetic base for specific chromosomes (or chromosome regions) should be based on analysis with these and other genetic markers available in potato.