Screening additional wild tomatoes for resistance to the whitefly-borne tomato yellow leaf curl virus

Plants of 25 wild Lycopersicon accessions were screened in the greenhouse for resistance to the whitefly-borne tomato yellow leaf curl virus (TYLCV). High levels of resistance were detected in 7 of 9 accessions of L. peruvianum and in all 5 accessions of L. chilense tested. In contrast, plants of 7 accessions of L. hirsutum and 3 of 4 accessions of L. pimpinellifolium were highly susceptible. Plants of accession CIAS 27 (L. pimpinellifolium) showed moderate resistance to TYLCV.     

Replication of tomato yellow leaf curl virus (TYLCV) DNA in agroinoculated leaf discs from selected tomato genotypes

The leaf disc agroinoculation system was applied to study tomato yellow leaf curl virus (TYLCV) replication in explants from susceptible and resistant tomato genotypes. This system was also evaluated as a potential selection tool in breeding programmes for TYLCV resistance. Leaf discs were incubated with a head-to-tail dimer of the TYLCV genome cloned into the Ti plasmid ofAgrobacterium tumefaciens. In leaf discs from susceptible cultivars (Lycopersicon esculentum) TYLCV single-stranded genomic DNA and its double-stranded DNA forms appeared within 2–5 days after inoculation. Whiteflies (Bemisia tabaci) efficiently transmitted the TYLCV disease to tomato test plants following acquisition feeding on agroinoculated tomato leaf discs. This indicates that infective viral particles have been produced and have reached the phloem cells of the explant where they can be acquired by the insects. Plants regenerated from agroinfected leaf discs of sensitive tomato cultivars exhibited disease symptoms and contained TYLCV DNA concentrations similar to those present in field-infected tomato plants, indicating that TYLCV can move out from the leaf disc into the regenerating plant. Leaf discs from accessions of the wild tomato species immune to whitefly-mediated inoculation,L. chilense LA1969 andL. hirsutum LA1777, did not support TYLCV DNA replication. Leaf discs from plants tolerant to TYLCV issued from breeding programmes behaved like leaf discs from susceptible cultivars.The Hebrew University of Jerusalem, Faculty of Agriculture, Department of Field and Vegetable Crops     

Inheritance of resistance to the two-spotted spider mite from L. pimpinellifolium (Jusl.) Mill. accession ‘TO-937’

The two-spotted spider mite (Tetranychus urticae Koch) is an important pest of tomato (Lycopersicon esculentum Mill.) crops in temperate regions as this spider mite has a very large capacity for population increase and causes severe tomato yield losses. There is no described tomato cultivar fully resistant to this pest, although resistant accessions have been reported within the green-fruited tomato wild species L. pennellii (Corr.) D’Arcy and L. hirsutum Humb. & Bonpl. We observed a L. pimpinellifolium (Jusl.) Mill. accession, ‘TO-937’, which seemed to be completely resistant to mite attacks and we crossed it with the susceptible L. esculentum cultivar. ‘Moneymaker’ to obtain a family of generations consisting of the two parents, the F₁, the F₂, the BC₁ to L. esculentum, and the BC₁ to L. pimpinellifolium. This family was evaluated for mite resistance in a polyethylene greenhouse using an experimental design in 60 small complete blocks distributed along 12 double rows. Each block consisted of five F₂ plants in one row and one plant of each of the two parents, the F₁, the BC₁ to L. esculentum, and the BC₁ to L. pimpinellifolium in the adjacent row. Plants at the 10–15 leaf stage were artificially infested by putting on them two pieces of French bean leaf heavily infested with T. urticae. After two months, evaluations of infestation were made by visual observation of mite nets and leaf damage. Plants that were free of signs of mite reproduction on the top half were considered as resistant, plants with silky nets only on their basal leaves, intermediate, and plants with mite reproduction on both basal and top canopies were scored as susceptible. Dominance for resistance appeared because all the ‘To-937’, BC₁ to L. pimpinellifolium, and F₁ plants were resistant. Not all ‘Moneymaker’ plants behaved as susceptible because 35% of plants were intermediate. In the BC₁ to L. pimpinellifolium and the F₂, most plants were scored as resistant, only 7 % BC₁ and 3 % F₂ plants were intermediate, and a single F₂ plant (0.3 %) was susceptible. With these figures, resistance seemed to be controlled by either four or two genes according to whether segregation in the BC₁ or in the F₂, respectively, were considered. These results could in part be explained because of appearance of negative interplot interference due to the high frequency of resistant genotypes within most of the generations. Therefore, the family was evaluated again but using a different experimental design. In the new experiment, 16 ‘TO-937’, 17 ‘Moneymaker’, 17 F₁, 37 BC₁ to L. pimpinellifolium, 38 BC₁ to L. esculentum, and 125 F₂ plants were included. Each of these test plants was grown besides a susceptible ‘Moneymaker’ auxilliary plant that served to keep mite population high and homogeneous in the greenhouse. Negative interplot interference was avoided with this design and all the ‘TO-937’, F₁, and BC₁ to L. pimpinellifolium plants were resistant, all ‘Moneymaker’ test plants were susceptible, and 52 % BC₁ to L. esculentum and 25 % F₂ plants were susceptible, which fitted very well with the expected for resistance governed by a single dominant gene. The simple inheritance mode found will favour sucessful introgression of mite resistance into commercial tomatoes from the very close relative L. pimpinellifolium.     

Trichome‐based host plant resistance of Lycopersicon species and the biocontrol agent Mallada signata: are they compatible?

Trichome‐based host plant resistance of Lycopersicon (Solanaceae) species offers the potential to reduce pesticide use in tomato production, but its compatibility with biocontrol agents is largely unknown. The effect of trichome‐based host plant resistance on the lacewing biocontrol agent, Mallada signata, was assessed for five accessions of L. cheesmanii, four accessions of Lycopersicon hirsutum, two accessions of Lycopersicon pennellii, and one Lycopersicon esculentum cultivar. An intact leaf was isolated from the whole plant using Tangletrap to coat the petiole and 20 green peach aphids [Myzus persicae (Sulzer) (Homoptera: Aphididae)] were placed on the leaf surface. After 24 h, 10 lacewings were placed on the leaf. The numbers of dead, trapped by exudates, untrapped and predated lacewings and aphids, and the numbers that had left the leaf were recorded a further 24 h later. Differences in insect designations between accessions were analysed using ANOVA. A General Linear Model (GLM), consisting of the densities of each trichome type and leaf area, was fitted to the data to determine the role of trichomes on the observed effects on lacewings and aphids. Lacewing mortality was greater on one accession of L. pennellii and one accession of L. hirsutum than on L. esculentum. The GLM indicated that type IV trichomes decreased the numbers of aphids predated, and increased cannibalism and, along with type III trichomes, increased entrapment‐related predator mortality. Although there were no differences in the numbers of predated aphids, with the majority predated for all accessions, the compatibility of trichome‐based host plant resistance of Lycopersicon species and the biocontrol of aphids by lacewings is questionable.     

Salt tolerance in Lycopersicon species. V. Does genetic variability at quantitative trait loci affect their analysis?

 Salt tolerance was studied comparatively in three families derived from crosses between Lycopersicon esculentum Mill. and two related wild species [two accessions of Lycopersicon pimpinellifolium (Jusl.) Mill. and one accession of Lycopersicon chesmannii f.minor (Hook.f.) Mull.] by means of QTL analysis of fruit yield and earliness under conditions of salinity. From six polymorphic genomic regions involved in salt tolerance, three contained segregant salt-tolerant QTLs for the three families; two were found only in both families derived from L.pimpinellifolium; and one, involved in fruit number, was detected only in one of the L.pimpinellifolium families. Some differences regarding the effects of the wild alleles at orthologous QTLs were found. These effects were always negative in the L. chesmannii family. Comparing both L. pimpinellifolium families, the “wild” alleles at two out of nine common QTLs for fruit number and weight had effects with opposite directions, and the mode of gene action was clearly different at five of them. QTL analysis of earliness revealed the largest genotypic differences among families. Most drastic differences were found for the epistatic interactions in which all genomic regions containing QTLs were involved. These interactions between unlinked genes increased the range of variation of means, mainly upwards, as compared with genotypes at individual QTLs. Only one (affecting fruit weight) out of 27 interactions was detected in both L.pimpinellifolium families. Heterotic effects found for salt tolerance in one of the families can be explained by the presence of overdominant (or pseudo-overdominant) and dominant gene effects at QTLs controlling final fruit yield under conditions of salinity. Allelic variation at salt-tolerant QTLs exists, changing the additive and, mainly, the non-additive components of the genotypic value. Consequently, it may negatively affect the general applicability (or efficiency) of marker-assisted selection to improve salt tolerance in other segregant populations where QTLs were not studied. The use of more informative co-dominant markers, like microsatelites, might overcome these problems. Received: 5 August 1996/Accepted: 25 October 1996     

Genetic diversity and geographic pattern in early South American cotton domestication

Amplified fragment length polymorphism fingerprinting was applied to survey the genetic diversity of primitive South American Gossypium barbadense cotton for establishing a possible link to its pre-Columbian expansion. New germplasm was collected along coastal Peru and over an Andean transect in areas where most of the archaeological evidence relating to cotton domestication has been recorded. Gene bank material of three diploid (G. raimondii, G. arboreum, and G. herbaceum) and four allotetraploid cotton species (G. hirsutum, G. mustelinum, G. tomentosum and additional G. barbadense) was added for inter- and intra-specific comparison. Eight primer combinations yielded 340 polymorphic bands among the 131 accessions. The obtained neighbor joining and unweighted pair-group method with arithmetic means are in full agreement with the known cytogenetics of the tetraploid cottons and their diploid genome donors. The four tetraploid species are clearly distinct based on taxonomic classification. The genetic diversity within G. barbadense reveals geographic patterns. The locally maintained cottons from coastal Peru display a distinct genetic diversity that mirrors their primitive agro-morphological traits. Accessions from the northernmost coast of Peru and from southwestern (SW) Ecuador cluster basal to the east-of-Andes accessions. The remaining accessions from Bolivia, Brazil, Columbia, Venezuela, and the Caribbean and Pacific islands cluster with the east-of-Andes accessions. Northwestern Peru/SW Ecuador (the area flanking the Guayaquil gulf) appears to be the center of the primitive domesticated G. barbadense cotton from where it spread over the Andes and expanded into its pre-Columbian range.This publication is dedicated to Prof. Dr. Drs.h.c. Gerhard Röbbelen on the occasion of his 75th birthday     

Genetic variation inSolanum pennellii: Comparisons with two other sympatric tomato species

Genetic variation—primarily in 19 genetic loci of seven enzyme systems—was analyzed in accessions from various parts of the geographic range ofSolanum pennellii, which according to all tested biosystematic criteria behaves like a species ofLycopersicon. In comparison with the largely sympatricL. hirsutum andL. pimpinellifolium, this species exhibits the same trends of reduced allogamy and decreased genetic variation toward the north and south margins of its distribution, though to a much lesser degree; it does not exhibit their trends toward smaller flower size in the same peripheral regions. All three species agree to a considerable extent in the ranking of their tested loci in respect to degree of variablility; however, overall polymorphy is highest inS. pennellii. Except for the appearance of self-compatibility at its southernmost margin,S. pennellii is exclusively and rigidly self-incompatible. Alleles are distributed much more uniformly over the range than in the previously mentioned species, marginal and internal endemic mutants being much less abundant. A marked geographic disagreement is evident in regions of high and low variation. These differences in patterns of genetic variability are reconciled in terms of observed differences in mating systems, probable age of distributions, and adaptive strategies.     

fw 2.2:a major QTL controlling fruit weight is common to both red- and green-fruited tomato species

We have shown that a major QTL for fruit weight (fw2.2) maps to the same position on chromosome 2 in the green-fruited wild tomato species, Lycopersicon pennellii and in the red-fruited wild tomato species, L. pimpinellifolium. An introgression line F₂ derived from L. esculentum (tomato) x L. pennellii and a backcross 1 (BC₁) population derived from L. esculentum x L. pimpinellifolium both place fw2.2 near TG91 and TG167 on chromosome 2 of the tomato highdensity linkage map. fw2.2 accounts for 30% and 47% of the total phenotypic variance in the L. pimpinellifolium and L. pennellii populations, respectively, indicating that this is a major QTL controlling fruit weight in both species. Partial dominance (d/a of 0.44) was observed for the L. pennellii allele of fw 2.2 as compared with the L. esculentum allele. A QTL with very similar phenotypic affects and gene action has also been identified and mapped to the same chromosomal region in other wild tomato accessions: L. cheesmanii and L. pimpinellifolium. Together, these data suggest that fw2.2 represents an orthologous QTL (i.e., derived by speciation as opposed to duplication) common to most, if not all, wild tomato species. High-resolution mapping may ultimately lead to the cloning of this key locus controlling fruit development in tomato.     

Distribution of acid invertase in the tomato plant

Acid invertase activity in Lycopersicon esculentum was highest in the locular wall of ripe fruit and lowest in roots. Activity was greater in leaf laminae than in petiole tissue and increased with leaf age, whereas there was more invertase in the upper part of the stem compared with the older portion. Activity in whole fruit increased with increasing ripeness and was greatest in overripe fruit. Of various tissues from a number of wild tomato species examined, the fruit of L. pimpinellifolium were particularly rich in the enzyme, in contrast to the fruit of L. hirsutum, L. hirsutum, var. glabratum and L. peruvianum which had low activity.     

Foliar pubescence and resistance to potato moth, Phthorimaea operculella, in Lycopersicon hirsutum

Pubescence characteristics for six accessions of Lycopersicon hirsutum Dunal and five accessions of L. hirsutum f. glabratum CH Mull. were determined and compared with those of an accession of cultivated tomato (L. esculentum Mill.). Removal of trichome exudates from excised leaflets using ethanol solution resulted in a reduced mortality and increased survival of potato moth (Phthorimaea operculella (Zeller)) neonates for the accessions that were most lethal when not treated with ethanol solution. No such treatment effect was evident for L. esculentum or for the L. hirsutum accession with least effect on neonates when its trichomes were intact. In a glasshouse experiment with caged intact plants, mortality of neonate P. operculella placed on the abaxial surface was greater on seven accessions than for L. esculentum.Neonates were less severely affected on the adaxial surface. Eleven days after inoculation, no live larvae were found on LA 1927, PI 127827, PI 134418, and PI 134428, and numbers on other accessions were lower than for L. esculentum. Eventual emergence of adults followed a similar trend. Multiple regression of insect data against pubescence indicated a significant correlation between density of type IV and VI trichomes and neonate mortality, decreased larval development and decreased adult emergence. Non-glandular type V trichomes were positively correlated with high survival of insects to 11 days and to adult. Though factors other than glandular trichomes are likely to be important, increased density of type IV and VI, along with reduced type V, are shown to be important to select in breeding for P. operculella resistance.     

Influence of Root and Content on the Temperature Response of Net and Uptake in Chilling Sensitive and Chilling Resistant Lycopersicon Taxa

We studied the influence of internal ammonium and nitrate contenton the temperature response of ammonium and nitrate uptake inboth chilling sensitive and chilling resistant tomatoes. Threetaxa were examined: Lycopersicon esculentum Mill. cv. T-5, achilling sensitive cultivar, Lycopersicon hirsutum Humb. andBompl. LA 1264, a wild, chilling sensitive accession from thelowlands of Ecuador, and Lycopersicon hirsutum LA1778, a chillingresistant accession from the highlands of Peru. Short exposures(4 h) of L. esculentum cv. T-5 to chilling temperatures irreversiblyinhibited ammonium absorption for at least 6 h. Nitrate absorptionin this taxon and ammonium and nitrate absorption in the L.hirsutum accessions recovered fully and immediately from suchexposures. The chilling resistant accession, L. hirsutum LA1778,showed a lower Q₁₀ for ammonium absorption (1?54?0?10, mean?s.e.)than its chilling sensitive relatives, L. hirsutum LA1264 (2?37?0?35)and L. esculentum cv. T-5 (1?92?0?11). The temperature responseof nitrate absorption depended on internal nitrate status; plantsgrown at high levels of ammonium and nitrate (200 mmol m^–3)showed higher Q₁₀'s for nitrate uptake (2?29?0?10) than thosedepleted of internal (1?86?0?12). Key words: Lycopersicon, ammonium, nitrate, temperature response, chilling     

Mitochondrial DNA Sequence Divergence among Lycopersicon and Related Solanum Species

Sequence divergence among the mitochondrial (mt) DNA of nine Lycopersicon and two closely related Solanum species was estimated using the shared fragment method. A portion of each mt genome was highlighted by probing total DNA with a series of plasmid clones containing mt-specific DNA fragments from Lycopersicon pennellii. A total of 660 fragments were compared. As calculated by the shared fragment method, sequence divergence among the mtDNAs ranged from 0.4% for the L. esculentum-L. esculentum var. cerasiforme pair to 2.7% for the Solanum rickii-L. pimpinellifolium and L. cheesmanii-L. chilense pairs. The mtDNA divergence is higher than that reported for Lycopersicon chloroplast (cp) DNA, which indicates that the DNAs of the two plant organelles are evolving at different rates. The percentages of shared fragments were used to construct a phenogram that illustrates the present-day relationships of the mtDNAs. The mtDNA-derived phenogram places L. hirsutum closer to L. esculentum than taxonomic and cpDNA comparisons. Further, the recent assignment of L. pennellii to the genus Lycopersicon is supported by the mtDNA analysis.     

Molecular tagging of the Am gene from Lycopersicon hirsutum f. glabratum PI 134417 using AFLP markers

Recently important epidemics caused by Alfalfa Mosaic Virus (AMV) have been reported in field grown canning tomatoes in southern Italy. The Am resistance gene identified in Lycopersicon hirsutum PI 134417 confers a complete resistance to several isolates of AMV with different geographical and botanical origins. In order to identify linked molecular markers, a segregant back-cross population of 120 individuals was obtained from the intraspecific cross between the resistant L. hirsutum accession PI 134417 and the susceptible accession L. hirsutum PI 247087. Using bulked segregant analysis combined with AFLP technology, four AFLP markers were found to be linked to the Am resistance gene. This gene will be assigned to a tomato chromosome using L. pennellii introgression lines.     

Development and mapping of SNP assays in allotetraploid cotton

A narrow germplasm base and a complex allotetraploid genome have made the discovery of single nucleotide polymorphism (SNP) markers difficult in cotton (Gossypium hirsutum). To generate sequence for SNP discovery, we conducted a genome reduction experiment (EcoRI, BafI double digest, followed by adapter ligation, biotin–streptavidin purification, and agarose gel separation) on two accessions of G. hirsutum and two accessions of G. barbadense. From the genome reduction experiment, a total of 2.04 million genomic sequence reads were assembled into contigs with an N₅₀ of 508 bp and analyzed for SNPs. A previously generated assembly of expressed sequence tags (ESTs) provided an additional source for SNP discovery. Using highly conservative parameters (minimum coverage of 8× at each SNP and 20% minor allele frequency), a total of 11,834 and 1,679 non-genic SNPs were identified between accessions of G. hirsutum and G. barbadense in genome reduction assemblies, respectively. An additional 4,327 genic SNPs were also identified between accessions of G. hirsutum in the EST assembly. KBioscience KASPar assays were designed for a portion of the intra-specific G. hirsutum SNPs. From 704 non-genic and 348 genic markers developed, a total of 367 (267 non-genic, 100 genic) mapped in a segregating F₂ population (Acala Maxxa × TX2094) using the Fluidigm EP1 system. A G. hirsutum genetic linkage map of 1,688 cM was constructed based entirely on these new SNP markers. Of the genic-based SNPs, we were able to identify within which genome (‘A’ or ‘D’) each SNP resided using diploid species sequence data. Genetic maps generated by these newly identified markers are being used to locate quantitative, economically important regions within the cotton genome.     

Resistance to the potato cyst-nematode, Heterodera rostochiensis, in the plant genus Lycopersicon

Forty-eight lines of Lycopersicon and four lines of Solanum were screened for resistance to twelve Heterodera rostochiensis populations of known patho-type(s). Plant lines were assessed for resistance first by examining the outside of the root ball for cysts and later by washing the root ball to extract all cysts. Possible resistant plant selections were re-tested against three eelworm populations, including the one to which they were first shown resistant. Resistance was discovered in two lines of Lycopersicon pimpinelli-folium, two L. esculentum L. pimpinellifolium crosses, L. esculentum var. cerasiforme, six lines of L. peruvianum, in L. peruvianum var. humifusum, L. hirsutum var. glabratum, and in Solanum indicum. Because resistance was found most commonly in L. peruvianum and because it has already been used as a resistant parent in breeding programmes to incorporate resistance to root-knot nematode (Meloidogyne spp.) in tomato, L. peruvianum seems to be the best source of resistance among plants tested so far. The host-parasite relationships of resistant L. hirsutum var. glabratum (B 6013) were compared with those of a commercial, susceptible tomato, L. esculentum‘Ailsa Craig’. Plants were inoculated with three eelworm isolates; the extent of eelworm invasion, plant reaction and eelworm development were studied. Larvae invaded and penetrated roots of the resistant plant as freely and in as large numbers as they penetrated roots of the susceptible tomato. In the latter, numerous larvae matured while, in contrast, few larvae matured in the roots of L. hirsutum var. glabratum. L. hirsutum var. glabratum was shown to possess a root diffusate as active in hatching larvae of Heterodera rostochiensis as that of L. esculentum‘Ailsa Craig’. The existence of pathotypes of H. rostochiensis, identifiable by their differing abilities to increase on resistant tomato lines, was not clearly revealed in the experiments.     

Advanced backcross QTL analysis in tomato. I. Identification of QTLs for traits of agronomic importance from Lycopersicon hirsutum

 Advanced backcross QTL (AB-QTL) analysis is a new strategy for studying the effect of unadapted alleles on the agronomic performance of elite cultivated lines. In this paper we report results from the application of the AB-QTL strategy to cultivated tomato using the wild species Lycopersicon hirsutum LA1777 as the donor parent. RFLP genomic fingerprints were determined for 315 BC₂ plants and phenotypic data were collected for 19 agronomic traits from approximately 200 derived BC₃ lines which were grown in replicated field trials in three locations worldwide. Between 1 and 12 significant QTLs were identified for each of the 19 traits evaluated, with a total of 121 QTLs identified for all traits. For 25 of the QTLs (20%) corresponding to 12 traits (60%), the L. hirsutum allele was associated with an improvement of the trait from a horticultural perspective, despite the fact that L. hirsutum is overall phenotypically inferior to the elite parent. For example, L. hirsutum has fruit that remains green when ripe (lack of red pigment) yet alleles were found in this species that significantly increase red color when transferred into cultivated tomatoes. Wild alleles were also associated with increases in total yield and soluble solids (up to 15%) and brix×red yield (up to 41%). These results support the idea that one cannot predict the genetic potential of exotic germplasm based on phenotype alone and that marker-based methods, such as the AB-QTL strategy, should be applied to fully exploit exotic germplasm. Received: 27 October 1997 / Accepted: 25 November 1997     

Genetic Diversity and Phylogenetic Relationships in the Genus Lycopersicon (Tourn.) Mill. as Revealed by Inter-Simple Sequence Repeat (ISSR) Analysis

Inter-simple sequence repeat (ISSR) analysis was for the first time used to study the genetic diversity and phylogenetic relationships in 54 wild accessions and cultivars of the genus Lycopersicon. Analysis involved 14 ISSR primers homologous to microsatellite repeats and containing additional selective anchor nucleotides. In total, 318 ISSR fragments were amplified for the wild and cultivated tomato genomes. The interspecific polymorphism revealed with the ISSR primers was 95.6%. Species-specific ISSR fragments were detected for each tomato species. The highest number (more than 20) of species-specific fragments were obtained for L. esculentum sensu lato, although the intraspecific variation of ISSR patterns was low. UPGMA cluster analysis was used to construct a dendrogram and to estimate the genetic distances between the species of the genus Lycopersicon; between populations ofL. peruvianum, L. pimpinellifolium, and L. esculentum; and between tomato cultivars. The ISSR-based phylogeny was generally consistent with Lycopersicon taxonomy based on morphological and molecular evidence, suggesting the applicability of ISSR analysis for genotyping and phylogenetic studies in tomato.     

Rates of cross-pollination inLycopersicon pimpinellifolium: Impact of genetic variation in floral characters

Cross-pollination was tested between different genotypes ofLycopersicon pimpinellifolium in an experimental plot situated in the southerly range of the species. Rates of cross-pollination were found to be highly correlated with flower size and were related to a lesser extent with degree of stigma exsertion. Comparisons of fertility suggest that exsertion of 1.5 mm or more from the anther tube orifice interferes with automatic self-pollination, thereby increasing rates of cross-pollination. A single species ofExomalopsis (Anthophoridae), observed to visit all tested genotypes ofL. pimpinellifolium, was responsible for most of the pollination. Other species of solitary bees and other bee families participated in cross-pollination.     

A simple plant regeneration-ability assay in a range of Lycopersicon species

Plant growth regulator-dependent (PGR-dependent) in vitro shoot organogenesis has been extensively studied in tomato (Lycopersicon esculentum), whereas PGR-independent adventitious shoot organogenesis received marginal attention in L. esculentum and no consideration at all in other Lycopersicon species. In the present study, induction of PGR-independent adventitious shoots was by decapitation of the apex and removal of preexisting shoot meristems of the seedling, and seedling culture on a medium with no PGR supplements. The existence of PGR-independent regeneration-ability was verified in L. esculentum genotypes (high pigment photomorphogenic mutants and wild-type counterparts) and was uncover amongst L. cheesmanii, L. chilense, L. chmielewskii, L. hirsutum, L. parviflorum, L.␣peruvianum and L. pimpinellifolium. Compared to species other than L. esculentum, high pigment photomorphogenic mutants displayed the weakest PGR-independent regeneration-ability. Our results imply that decapitated seedlings cultured on a medium without PGRs can serve as a convenient assay system for genotypic variation in self-controlled, PGR-independent, shoot regeneration-ability in a wide range of Lycopersicon species. Using transverse thin slices of the hypocotyl placed onto a medium supplemented with 0.2 μM zeatin reboside and 0.04 μM IAA, we assessed PGR-mediated shoot regeneration in L. esculentum genotypes. In a given genotype, more plants per seedling were established by PGR-mediated than by PGR-independent regeneration. However, with both modes of organogenesis, only a fraction of shoot buds eventually grew into normal plants, while others developed into abnormal regenerants having no stem. Percentage of stem-deficiency, in a given genotype, was higher in PGR-treated cultures, which indicates that PGRs amplify the formation frequency of imperfect adventitious apical shoot meristems. Unlike L. esculentum, adventitious shoot buds of other Lycopersicon species, induced by wounding seedlings that were not treated with PGRs, rarely formed regenerants lacking a stem.     

Breeding for flavour of fresh market tomato: sources for increasing acid content

Breeding programs in tomato for fresh consumption have concluded in very productive varieties/hybrids with an extraordinary external quality. However, internal quality has not been a priority objective in these breeding programs, so present products have a lack of important internal quality properties. Thus, internal and nutritional improvement including taste and organoleptyc characteristics are important breeding objectives at present. A screening trial to identify sources for internal quality improvement by increasing acid content was carried out. 12 accessions of Lycopersicon esculentum and 8 of L. pimpinellifolium were tested with that purpose. Content in citric, malic, oxalic and fumaric acid by HPLC, soluble solids content (SSC)(1 Brix) by refractometry and total acidity by titration with NaOH were measured. Sources for high citric, malic and fumaric acid content were found to begin those breeding programs. Results could possibly suggest an independent genetic control for every acid.