Diversification of andromonoecy in Solanum section Lasiocarpa (Solanaceae): the roles of phenotypic plasticity and architecture

Quantitative analyses of sexual expression show extensive interspecific variation in the strength of andromonoecy (proportions of hermaphroditic and staminate flowers) among Solanum species in the monophyletic section Lasiocarpa. The roles of phenotypic plasticity and inter- and intra-inflorescence architecture in the diversification of andromonoecy within this small clade were analyzed. Four species that represent a range of expression of andromonoecy were examined. Staminate flowers produced within inflorescences ranged from 3% (S. candidum) to 7% (S. ferox) in weakly andromonoecious species and from 39% (S. pseudolulo) to 60% (S. quitoense) in more strongly andromonoecious species. Manipulation of fruit set on clonal replicates of multiple genotypes demonstrated variation among species for phenotypic plasticity. The strongly andromonoecious species, S. pseudolulo and S. quitoense, were not plastic and produced a large proportion of staminate flowers regardless of fruiting treatment, whereas S. candidum and S. ferox were phenotypically plastic and produced significantly more staminate flowers in the presence of developing fruit. Staminate flower production of all four species varied both within and among inflorescences. A greater proportion of staminate flowers were produced in distal (later produced) inflorescences. Within inflorescences, hermaphroditic flowers occurred in basal positions, whereas staminate flowers, when produced, occurred more distally. This pattern of staminate flower production is qualitatively the same in all species investigated; however, quantitative variation in the transition from hermaphroditic to staminate flower production within and among inflorescences is associated with variation in the strength of andromonoecy. At least three factors have contributed to the diversification of andromonoecy in section Lasiocarpa including the presence or absence of phenotypic plasticity in response to fruit set, quantitative variation in intra- and inter-inflorescence architectural effects, and total flower production.     

A revision of Solanum section Brevantherum (Solanaceae)

The present revision of Solatium sect. Brevantherum Seithe recognizes 27 species in North and South America, two of which have become naturalized in parts of the Old World. Three species,S. lltisii, S. Goodspeedii, and S. appressum, are described as new. Comparative morphology, geographical distribution, and ecological data provide evidence for species recognition. Some of the most diagnostic features are those associated with the buds, leaves, and the hairs, which range from simple to porrect-stellate and more complex types, described herein as multangulate, dendritic-multangulate, echinoid, and dendriticechinoid.     

Seed coat structure and development in Solanum L. section Solanum (Solanaceae)

Seed coat structure in Solanum L. section Solanum (Solanaceae). Seed coat structure in Solanum L. section Solanum was examined using SEM. The seed coat patterns observed were fairly uniform throughout the section, and thus of little diagnostic use. Moreover, all species are characterized by their seeds being covered by hairlike structures, which are bands of lignified thickening in the lateral (and basal) walls of the outer epidermal cells of the testa, and which only become obvious when the seeds are wetted. The development of the seed coat and its characteristic thickening was followed from the unfertilized ovule to the mature seed in vouchered material of Solanum nigrum L. since this species is the generic type, using sections of freshly fixed material.     

Correlated evolution of fruit size and sexual expression in andromonoecious Solanum sections Acanthophora and Lasiocarpa (Solanaceae)

Andromonoecy is hypothesized to evolve as a mechanism enabling plants to independently allocate resources to female and male function. If staminate flower production is a mechanism to regulate allocation to female function (i.e., fruit production), then large-fruited species should be more strongly andromonoecious than smaller-fruited taxa because more resources are required to mature large fruit. We combined phylogenetically independent contrast analyses with extensive phenotypic characterization under common greenhouse conditions to examine the predicted relationship between fruit mass and the strength of andromonoecy among 13 species in Solanum sections Acanthophora and Lasiocarpa. The strength of andromonoecy, defined as the proportion of staminate flowers produced within inflorescences, was significantly and positively associated with fruit mass in both na?ve and phylogenetically independent analyses. Our results are consistent with the hypothesis that andromonoecy functions as a mechanism to regulate allocation to female function and suggest that the strength of andromonoecy is also associated with resource limitation. In general, we find that strong andromonoecy appears to arise via reductions in hermaphroditic flower number. However, increases in staminate flowers have also contributed to transitions to strong andromonoecy in certain species. Finally, our analyses identified a suite of correlated characters (flower size, ovary width, fruit mass) that are associated with changes in the sexual expression of andromonoecy.     

New species of Solanum section Geminata (Solanaceae) from South America

Fourteen new species ofSolanum sectionGeminata are described and illustrated. Eight of these,S. erosomarginatum, S. foetens, S. lasiocladum, S. lucens, S. ombrophilum, S. tanysepalum, S. tenuiflagellatum, andS. turgidum are from Venezuela.Solanum cucullatum andS. bellum are from Ecuador,S. abitaguense from Ecuador and northeastern Peru,S. amnicola andS. yanamonense from eastern Peru, andS. mapiricum from eastern Bolivia. Relationships of each of the species to others in its geographical area are discussed. Chromosome numbers are reported for ten of these new species.     

Five new species of Solanum section Geminata (Solanaceae) from South America

Five new species of South AmericanSolanum are described:S. morii from French Guiana,S. superbum andS. tumescens from Bolivia,S. platycypellon from southern Bolivia and northern Argentina andS. gertii from southeastern Brazil. An illustration and distribution map for each species is provided and relationships to close relatives are discussed.     

Graft formation in Solanum pennellii (Solanaceae)

Three phases of cohesion were observable during the development of compatible autografts in Solanum pennellii. Phase I cohesion 1) lasted 4–5 d after grafting, 2) was characterized by an average increase in tensile strength of 4 g breaking weight (BW) mm^–2 graft area (GA) d^–1, and 3) correlated positively with cellular interdigitation at the graft interface. The fresh weight of the scion increased by approximately 5% d^–1 during the first 2 d after grafting. Phase II cohesion occurred 5–15 d after grafting, during which time 1) the tensile strength of the graft union increased by 14 g BW mm^–2 GA d^–1, 2) vascular differentiation across the graft interface was completed, and 3) the fresh weight of the scion increased by 9% d^–1. Phase III cohesion occurred subsequent to 15 d after grafting, during which time 1) the tensile strength of the graft union leveled off at a value similar to that of an ungrafted internode, and 2) the fresh weight of the scion increased by 14% d^–1. These results are discussed relative to mechanisms underlying the formation of compatible grafts.     

Karyotype studies in South American species of Solanum subgen. Leptostemonum (Solanaceae)

Mitotic chromosome numbers and karyotypes of 13 South American species (12 native and one naturalized) from four sections of SOLANUM subgen. LEPTOSTEMONUM were studied. Chromosome numbers of S. ACERIFOLIUM, S. AENICTUM, S. CONDITUM, S. CONSIMILE, S. INCARCERATUM, and S. PLATENSE are reported for the first time. The number 2n = 24 was found in most species, while 2n = 22 was found in S. MAMMOSUM and S. PLATENSE. The latter is the second SOLANUM with this unusual number. Satellites are always present and were visible in more than 50 % of the cells studied. Karyotypes are symmetrical: M and SM chromosomes are common, whereas ST chromosomes are rare. The karyotypes of S. AENICTUM, S. MAMMOSUM, and S. PANICULATUM are comparatively asymmetrical. Species can be distinguished by a combination of chromosome number, karyotype formulae, karyotype length, the position of satellites in a particular chromosome pair, and asymmetry indices. The phenogram obtained does not reflect the sectional arrangements or the systematic affinities of the species studied. In sect. ACANTHOPHORA, increased asymmetry is associated with derived characters (strong andromonoecy, winged seeds, mammiform fruits). Diversification in the subgenus is suggested to be related to visible chromosome rearrangements and cumulative, cryptic structural changes may have also played a relevant evolutionary role.     

Features related to anther opening in Solanum species (Solanaceae)

The mode of anther opening and the morphological and histological variability of the stomium are described in 30 Solanum species. Poricidal, poricidal‐longitudinally dehiscing and longitudinally dehiscing anthers are observed. In the three types, the stomium may be diverse with regard to shape and histological characteristics before opening, but is always composed of small epidermal cells as the sole anther wall layer; the stomial cells may be differentiated only in part of the anther length. Particular crescent‐shaped structures in the epidermis, called ‘ridges’, are observed to line the stomium in most species. These ridges may be related to the stomium opening, working together with the cells with thickened walls of the anther. Cells with thickened walls are developed in the endothecium, middle layers and/or connective tissue at the apical end of the anther, surrounding the pore; only in the longitudinally dehiscing anthers of S. nitidum does an endothecium with thickened cell walls develop along its entire length. At least two histological features (the differentiation of small stomial epidermal cells as a unique layer, and the distribution of cells with thickened walls) seem to constrain the form of the open stomium. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 344–354.     

Architectural effects mimic floral sexual dimorphism in Solanum (Solanaceae)

Factors underlying apparent floral sexual dimorphism were examined in six species of andromonoecious Solanum section Lasiocarpa (Solanaceae). Both multivariate and univariate analyses show that hermaphroditic flowers are significantly larger than staminate flowers for all features measured. Thus, flowers could be characterized as sexually size dimorphic. However, when size variation due to flower position (architecture) is controlled experimentally, differences between the floral genders for the nongynoecial characters disappear; there is no difference in corolla or androecium size. Staminate flowers appear to be generally smaller than hermaphroditic flowers, not because of any difference related to primary sexual function, but because they tend to occur in the distal regions of each inflorescence. In contrast, significant differences between hermaphroditic and staminate flowers for primary female traits (ovary, style, and stigma) remain after controlling for position: the two floral types are truly dimorphic for these characters. We show that consideration of architectural effects can direct and refine hypotheses concerning the evolution of andromonoecy. More generally, if architectural effects on flower size are common among taxa with unisexual flowers, then these effects may contribute to the common perception of size dimorphism in taxa with unisexual flowers.     

Karyological studies in Jaborosa (Solanaceae)

Sixteen species of Jaborosa (Solanaceae), including eight endemic to Argentina, were studied karyologically. The numbers n  = 12 and/or 2n  = 24 were found in all species, the majority of the cases being new reports. Mitotic chromosomes were small- to medium-sized, the average length varying from 2.95 to 4.93 µm. All species had one to three chromosome pairs with satellites. The karyotypes, obtained for 13 species, were slightly asymmetrical: A ₁ ranged from 0.228 to 0.483, A ₂ ranged from 0.095 to 0.182, and Paszko's asymmetry index ranged from 0.84 to 3.47. In all species, metacentric chromosomes were the most common, followed by submetacentrics, but subtelocentrics were rare. Morphological similarities and sectional arrangements were not reflected in either a principal components analysis plot or asymmetry index plot, but the species could be singled out by their karyotype formulae and the different karyotype parameters taken. In Jaborosa , a notably diversified genus, exo-morphological evolution has taken place, together with evident chromosome rearrangements, whose disposition is different and not as clear as in related genera.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 467–478.     

The variation and evolution of selected species of Solanum section Basarthrum (Solanaceae). II

Five taxa ofSolanum sect.Basarthrum were studied in an effort to clarify their taxonomic position and to determine the effective evolutionary mechanisms. Methods included an analysis of chromosome number and behavior, artificial hybridizations and a study of herbarium material. The data suggest thatS. canense andS. suaveolens are closely related and that 5.suaveolens may have been the progenitor ofS. canense. The only successful interspecific cross involving one of these two species was vigorous but highly sterile. Evidence from both morphology and crossing studies indicates a close relationship betweenS. basendopogon andS. caripense. Hybrids between these two species with relatively high fertility through the F₃ generation were secured. The status ofS. basendopogon f.obtusum remains a problem since there is but one collection of the typical form. The placement ofS. sanctae-marthae in sect.Basarthrum is considered problematic. Virtually none of 170 interspecific crosses with this species were successful. Seed size and the presence and size of a seed wing are proposed as useful morphological characters in sect.Basarthrum. There is apparently a correlation between short styles and self-compatibility. All species are diploid (n = 12) and no chromosomal or meiotic aberrations were noted in the species or hybrids. Most of the more than 1,000 interspecific crosses failed. Most of the hybrid fruits bore no seeds or seeds which did not germinate. The primary barriers separating species are considered to be strong prefertilization isolating mechanisms and ecogeographic factors.     

Observations on stylar heteromorphism in Solanum torvum Sw. (Solanaceae)

In several species of Solanum L. two forms of flower are noticeable in each inflorescence. In one form, the style is long and distinctly exserted; in the other, it is short and included within the conically connivent anthers, so that it is not visible from outside in an open flower. To this kind of difference in style length the term stylar heteromorphism has been applied here, just to distinguish it from heterostyly in the traditional sense. The phenomenon does not seem to have received much attention from botanists so far, and consequently rather little is known about its biological significance and possible evolutionary importance. The present report consists mainly of some observations made on stylar heteromorphism in one of these species, Solanum torvum , a shrubby weed widely distributed in the humid tropics.     

Correlated evolution of self-incompatibility and clonal reproduction in Solanum (Solanaceae)

It has been suggested that clonality provides reproductive assurance in cross-fertilizing species subject to pollen limitation, relieving one of the main selective pressures favoring the evolution of self-fertilization. According to this hypothesis, cross-fertilizing species subject to pollen limitation should often be clonal. Here, we investigated the association between clonality and a genetic mechanism enforcing outcrossing, self-incompatibility, in Solanum (Solanaceae). We collected self-incompatibility and clonality information on 87 species, and looked for an association between these two traits. To account for the contribution of shared evolutionary history to this association, we incorporated phylogenetic information from chloroplast (NADH dehydrogenase subunit F) sequence data. We found that self-incompatibility is strongly associated with clonal reproduction: all self-incompatible species reproduce clonally, while the absence of clonality is widespread among self-compatible taxa. The observed correlation persists after taking into account shared phylogenetic history, assumptions about the evolutionary history of self-incompatibility, uncertainty associated with phylogeny estimation, and associations with life history (annual/perennial). Our results are consistent with the hypothesis that clonality provides reproductive assurance, and suggest that the consequences of clonal growth in the evolution of plant reproductive strategies may be more significant than previously thought.     

AFLP markers support separation of Solanum nodiflorum from Solanum americanum sensu stricto (Solanaceae)

This study was aimed at examining the relationships between the African material of Solanum americanum (also designated as S. nodiflorum), accessions of this taxon from other geographical areas, and American S. americanum using AFLP markers. 96 individuals representing 39 accessions of S. americanum sensu lato and related diploid species from the widest possible geographical range, and one accession of S. dulcamara (as outgroup) were used. The AFLP results suggested that American S. americanum differs from S. nodiflorum and that the material investigated in this study can be assigned to three different species: S. americanum sensu stricto, S. nodiflorum and a Solanum species from Brazil. These species can be differentiated based on a combination of floral and fruit characteristics.     

Allozyme variation in the eggplant,Solanum melongena L. (Solanaceae)

Enzyme electrophoretic studies were made in cultivated Solanum melongena L. (eggplant) and similar wild and weedy forms, several of which have been thought to be different species/taxa. Twenty-nine accessions of S. melongena, 33 accessions of weedy forms (referred to as insanum) and 2 accessions of wild forms (referred to as incanum) were surveyed for 29 isozyme loci. In S. melongena, 22 of the 29 loci were monomorphic, and nearly all of its genes were either also monomorphic or in similar frequencies in insanum and incanum. The results demonstrate that the three taxa have a very close genetic relationship. The high genetic identities between them (0.913–0.967) suggests that they are conspecific even though they include extensive morphological diversity.     

Functional gametophytic self-incompatibility in a peripheral population of Solanum peruvianum (Solanaceae)

The transition from self-incompatibility to self-compatibility is a common transition in angiosperms often reported in populations at the edge of species range limits. Geographically distinct populations of wild tomato species (Solanum section Lycopersicon (Solanaceae)) have been described as polymorphic for mating system with both self-incompatible and self-compatible populations. Using controlled pollinations and sequencing of the S-RNase mating system gene, we test the compatibility status of a population of S. peruvianum located near its southern range limit. Pollinations among plants of known genotypes revealed strong self-incompatibility; fruit set following compatible pollinations was significantly higher than following incompatible pollinations for all tested individuals. Sequencing of the S-RNase gene in parents and progeny arrays was also as predicted under self-incompatibility. Molecular variation at the S-RNase locus revealed a diverse set of alleles, and heterozygosity in over 500 genotyped individuals. We used controlled crosses to test the specificity of sequences recovered in this study; in all cases, results were consistent with a unique allelic specificity for each tested sequence, including two alleles sharing 92% amino-acid similarity. Site-specific patterns of selection at the S-RNase gene indicate positive selection in regions of the gene associated with allelic specificity determination and purifying selection in previously characterized conserved regions. Further, there is broad convergence between the present and previous studies in specific amino-acid positions inferred to be evolving under positive selection.