Intermediate Leaf Morphology Research Articles

Phylogenomic and morphological data reveal hidden patterns of diversity in the national tree of Brazil, Paubrasilia echinata.

Paubrasilia echinata (common names, pau brasil, brazilwood) is the national tree of Brazil and an endangered species endemic to the Brazilian Atlantic Forest. Over its wide distribution of 2000 km, its leaflets morphology exhibits extensive plasticity. Three morphotypes are commonly identified based on leaf size, but it is unclear if they represent distinct taxa or a single polymorphic species. This study aims to clarify the taxonomic position of the three morphotypes to inform conservation decisions. A morphometric study of leaf characters of herbarium specimens was coupled with genetic analyses using genotype-by-sequencing data. We used maximum-likelihood and coalescent methods to evaluate the phylogenetic and population structure of the species. We compared these with a morphological dendrogram built from hierarchical clustering. Two of the three morphotypes formed separately evolving lineages, the third morphotype formed two geographically separate lineages, and northern trees with intermediate leaf morphology formed a separate fifth lineage. Leaflet size varied by over 35-fold, and although morphological clustering generally matched the genetic patterns, there were some overlaps, highlighting the cryptic diversity within this group. Our genetic and morphological results provide some evidence that cultivated trees from different states in Brazil seem to have a limited genetic origin and do not reflect the broader genetic and geographical diversity of the species. As a result, more care is likely needed to preserve the overall genomic diversity of this endangered and iconic species.

Interspecific hybridization among cultivars of hardy Hibiscus species section Muenchhusia.

Rose mallows belong to the Muenchhusia section of the Hibiscus genus. They represent a small group of cold tolerant North American plants and are popular ornamentals mainly because of their abundant, large and colorful flowers. Due to their geographical origin they are well suited for garden use in temperate regions worldwide. The aim of the study was to investigate hybridization barriers in crosses among cultivars of Hibiscus species from the Muenchhusia section: H. coccineus, H. laevis and H. moscheutos. Crossing barriers were identified as both pre- and post-zygotic. The analysis of pollen tube growth revealed inhibition of pollen tubes and their abnormal growth. In specific crosses the fertilization success was low. The pre-fertilization barriers did not cause a complete reproductive isolation between the hybridization partners. In relation to post-fertilization barriers, the occurrence of hybrid incompatibilities such as unviability, chlorosis, necrosis, stunted growth and albinism were the main drawback in production of hybrids. The appearance of symptoms of hybrid incompatibilities was dependent upon specific parental plants. The obtained progeny had intermediate leaf morphology and flower morphology compared to parental plants. Hybridity state was verified by morphological analysis and RAPD markers. Based on the overall plant morphology, 472 hybrid progenies were obtained.

Leaf morphological analyses in four European oak species (Quercus) and their hybrids: A comparison of traditional and geometric morphometric methods

In this study, leaf morphology was assessed in a mixed oak stand (western France) using two geometric morphometric (landmark and outline) datasets and one dataset of 19 leaf measures. Adult oaks (817 oaks), comprising four white oak species (Quercus petraea, Q. robur, Q. pubescens and Q. pyrenaica), were sampled for DNA extraction and genetic analysis (nuclear microsatellites). Leaf morphology was assessed on 336 oaks, comprising pure species and hybrids as determined by genetic assignment. This comparative study of oak leaf morphology, based on the use of two free size geometric morphometric methods and a set of leaf measurements, combined with the genetic assignment of individuals to pure species or hybrids, provided information about the differences among species and the intermediate leaf morphology of their hybrids.

Variation in leaf morphology of Quercus crispula and Quercus dentata assemblages among contact zones: a method for detection of probable hybridization

I describe variation in leaf morphology of Quercus crispula and Quercus dentata assemblages within and among their contact zones. Such relationships provide a relatively fast and accurate method for detecting hybridization. Using discriminant function (DF) analysis based on leaf characteristics, I was able to differentiate between these two species in pure zones. In three of five contact zones, the DF scores showed broad, continuous distributions with three or more peaks. The trees showing intermediate leaf morphology are considered to be hybrids. In the other two contact zones, the DF scores showed distinct bimodal distributions, suggesting that Q. crispula and Q. dentata rarely hybridize in these sites. Thus, the method described in this study should be effective for detecting probable hybridization between these two species in contact zones, and the relative frequency of hybridization among contact zones. However, there was likely to be intraspecific variation of Q. crispula between geographic ranges, restricting interpretations to patterns occurring within sites or limited geographic ranges.

Assessing the threat from hybridization to the rare endemic Physaria bellii Mulligan (Brassicaceae)

Hybridization of a rare endemic with a more common congener can endanger the rarer species through gene swamping. This study used a combination of genetic, morphological and cytological analyses to assess the threat to Bell’s twinpod ( Physaria bellii), a rare endemic restricted to the Colorado Front Range, from hybridization with its more widespread congener Physaria vitulifera. Two populations of P. bellii at the southernmost end of its range were suspected of containing hybrid plants, based on field observations of intermediate leaf morphology. Inter-simple sequence repeat (ISSR) marker analysis confirmed that suspect individuals contained alleles from both P. bellii and P. vitulifera, with most hybrids genetically closer to P. vitulifera. Morphological data from leaf measurements showed hybrids to be intermediate for several characters, with the exception of the leaf sinus trait that was statistically closer to P. vitulifera. The morphometric data supported the genetic data with Canonical Discriminant Analyses of both data sets showing similar patterns. The extent of the threat to P. bellii populations from hybridization with the more common P. vitulifera was assessed through cytological analysis of existing populations and through field and greenhouse crosses. While naturally occurring hybrids are tetraploid, diploid P. vitulifera populations do not occur close enough to the current range of diploid P. bellii to permit gene flow. Interspecific crosses yielded fewer normal seeds than intraspecific crosses, regardless of the ploidy levels of the parents. It does not appear that P. bellii is currently threatened by hybridization with P. vitulifera, and efforts to conserve this globally imperiled species should focus on the threat from potential habitat loss rather than from gene swamping.

Somatic hybrids between potato Solanum tuberosum and wild species Solanum verneï exhibit a recombination in the plastome

In the present survey, interspecific somatic protoplast fusion between a dihaploid cultivated potato Solanum L. tuberosum (BF15) and a wild species Solanum vernei (V3) has been performed using the PEG method. Five putative hybrids were first selected. Among them, only two were retained. DNA analysis, using flow cytometry, showed that the first hybrid (VB2) was dihaploid (2n=2x=24 chromosomes), whereas the second (VB1) was hexaploid (2n=6x=72 chromosomes). In the greenhouse, these putative hybrids showed that they were able of raising and producing large tubers but with a modified shape compared to parental ones. Furthermore, they harbored an intermediate leaf morphology compared to their parents. The hybrid nature of these plants was first confirmed according to their esterase and peroxidase isoenzyme patterns. The RAPD analysis of genomic DNA and microsatellite based amplification (I-SSR) showed that both clones VB1 and VB2 are asymmetric somatic hybrids. They seem to have eliminated the major part of V3 parental nucleus but not the totality. The analysis of chloroplast DNA suggests that both hybrid plastomes were the result of a recombination between parental ones.

Caipira sweet orange + Rangpur lime: a somatic hybrid with potential for use as rootstock in the Brazilian citrus industry

Protoplast culture following polyethylene glycol-induced fusion resulted in the regeneration of somatic hybrid plants between Caipira sweet orange (Citrus sinensis L. Osbeck) and Rangpur lime (C. limonia L. Osbeck). The plants were confirmed as somatic hybrids by leaf morphology, chromosome number and RAPD profile. All regenerated plants were tetraploid (2n = 4x = 36), with intermediate leaf morphology and complementary RAPD banding profile of both parents. This combination may be useful as a rootstock for the citrus industry in Southeastern Brazil since this somatic hybrid could combine the drought tolerance and vigor of Rangpur lime with the blight tolerance of Caipira sweet orange.

Variation in frost tolerance and seedling morphology of the spotted gums Corymbia maculata, C. variegata, C. henryi and C. citriodora

The frost tolerance of seedlings of spotted gums representing four closely related species; Corymbia maculata (seven provenances), C. variegata (six provenances), C. henryi (one provenance) and C. citriodora (two provenances) was examined. Each provenance of C. maculata, C. variegata and C. henryi was represented by 10 seedlings from each of eight open-pollinated families, while the two C. citriodora provenances were each represented by 40 seedlings from a provenance bulk seedlot. Excised leaf discs from seedlings hardened by exposure to the Canberra winter were subjected to test temperatures of –4.2, –6.1 and –8.0˚C. Damage to the discs was estimated by the electrical conductivity of leachate produced by soaking the disks in water after exposure to freezing temperatures. Exposure to –6.1˚C for 1 h produced leachate conductivities corresponding to 37% of discs receiving lethal injury and gave good discrimination between tolerant and susceptible material. There were significant differences in frost tolerance between species, provenances within species, and between open-pollinated families within provenances. Corymbia variegata displayed significantly greater frost tolerance than the other three species. Species rankings were consistent across the three test temperatures. Inland, high altitude provenances of C. variegata and C. maculata had greater frost tolerance than those from lowland coastal locations, while there were no consistent trends of frost tolerance with latitude in these species. Analysis of seedling morphological characters effectively separated the different species in a manner consistent with the taxonomic review by Hill and Johnson (1995). Characters which separated C. maculata and C. variegata included the leaf pair at which the changeover from juvenile to intermediate leaf morphology occurred and the degree of pubescence of the leaves and stem, leaf size and shape. Corymbia variegata and the southern provenance of C. citriodora were separated only by the citronella scent of C. citriodora, the northern C. citriodora provenance had distinctly different leaf size and shape.Corymbia henryi seedlings had greater stem and leaf pubescence than those of C. maculata as well as distinctly shaped leaves, characterised by having the greatest length from the widest point to the leaf base.

Somatic hybrids between the cultivated potato Solanum tuberosum L. and the 1EBN wild species Solanum pinnatisectum Dun.: morphological and molecular characterization

Interspecific somatic hybrids between the 1EBN-wild species Solanum pinnatisectum (S. pnt) and four different diploid breeding lines of Solanum tuberosum (S. tbr) were produced by electrofusion. S. pnt exhibits resistance to Phytophthora infestans and Erwinia blackleg. Somatic hybrids were identified by RFLP analysis using the oligonucleotide (GATA)4 as a probe. In three of four combinations all regenerates obtained were somatic hybrids. All 86 somatic hybrids between the breeding line H256/1 and S. pnt were analyzed in detail with respect to morphological and molecular characters; 50% of the somatic hybrids showed normal intermediate leaf morphology. Tubers of somatic hybrid plants grown in the greenhouse as well as in the field were evenly shaped and remarkably similar to those of the S. tbr breeding line. Analysis of relative DNA content by flow cytometry revealed that 75% of the somatic hybrids were tetraploid, some were hypotetraploid and others polyploid or mixoploid. Slotblot and RFLP analyses were carried out using repetitive and some single-copy DNA probes. The genome portion of the S. tbr breeding line was determined by slot-blot analysis using the species-specific repetitive probe pSA287. Obviously, most somatic hybrids contain the complete genomes of both fusion partners. In some of the somatic hybrids, a significantly lower intensity of the S. pnt-specific hybridization signal indicated a certain degree of asymmetry.

Somatic hybrids between Brassica oleracea and B. campestris: selection by the use of iodoacetamide inactivation and regeneration ability

An efficient procedure for obtaining somatic hybrids between B. oleracea and B. campestris has been developed. Hypocotyl protoplasts of B. oleracea were fused with mesophyll protoplasts from three different varieties of B. campestris by the polyethylene glycoldimethylsulfoxide method. The selection of somatic hybrids utilized the inactivation of B. oleracea protoplasts by iodoacetamide (IOA) and the low regeneration ability of B. campestris. The efficiency of recovery of somatic hybrids depended upon the IOA concentration, and when 15 mM IOA was used, 90% of the regenerated plants were found to be hybrid. The somatic hybrids were examined for i) leaf morphology, ii) leucine aminopeptidase (LAP) isozyme and iii) chromosome number. All the hybrids had intermediate leaf morphology and possessed LAP isozymes of both parental species. The chromosome analysis revealed a considerable variation in chromosome number of somatic hybrids, showing the occurrence of multiple fusion and chromosome loss during the culture. Some of the hybrids flowered and set seeds.