Fruit syndromes in Viburnum: correlated evolution of color, nutritional content, and morphology in bird-dispersed fleshy fruits

PREMISE

A key question in plant dispersal via animal vectors is where and why fruit colors vary between species and how color relates to other fruit traits. To better understand the factors shaping the evolution of fruit color diversity, we tested for the existence of syndromes of traits (color, morphology, and nutrition) in the fruits of Viburnum. We placed these results in a larger phylogenetic context and reconstructed ancestral states to assess how Viburnum fruit traits have evolved across the clade.

RESULTS

We find that blue Viburnum fruits are not very juicy, and have high lipid content and large, round endocarps surrounded by a small quantity of pulp. Red fruits display the opposite suite of traits: they are very juicy with low lipid content and smaller, flatter endocarps. The ancestral Viburnum fruit may have gone through a sequence of color changes before maturation (green to yellow to red to black), though our reconstructions are equivocal. In one major clade of Viburnum (Nectarotinus), fruits mature synchronously with reduced intermediate color stages. Most transitions between fruit colors occurred in this synchronously fruiting clade.

CONCLUSIONS

It is widely accepted that fruit trait diversity has primarily been driven by the differing perceptual abilities of bird versus mammal frugivores. Yet within a clade of largely bird-dispersed fruits, we find clear correlations between color, morphology, and nutrition. These correlations are likely driven by a shift from sequential to synchronous development, followed by diversification in color, nutrition, and morphology. A deeper understanding of fruit evolution within clades will elucidate the degree to which such syndromes structure extant fruit diversity.

Calycinal secretory structures in Calolisianthus pedunculatus (Cham. & Schltdl) Gilg (Gentianaceae): anatomy, histochemistry, and functional aspects

Secretory structures were little studied in Gentianaceae. Glandular areas on the calyx dorsal region are commonly reported for Helieae species, the main tribe of Gentianaceae. So, the elucidation of nature of glandular areas is particularly relevant. Trichomes secreting mucilage, interpreted as colleters, are reported only for the sepals of Gentianinae species. We aimed to anatomically characterize and identify the nature of the calycinal secretory structures in Calolisianthus pedunculatus. Samples from floral buds, flowers, and fruits were collected, fixed, and processed following usual procedures for light and scanning electron microscopies. Histochemical tests were performed to determine the nature of the secretion. Glucose, fructose, and sucrose were measured with an ELISA reader. Colleters occur on the sepal ventral region and are composed of a multicellular secretory head and a stalk. These structures secrete polysaccharides and proteins, and the secretion is probably released through cuticle microchannels. Nectaries, on the other hand, occur on the sepal dorsal region. They are formed by 3-5 cells arranged in rosettes circling a central cell or pore. These structures also secrete polysaccharides (mainly fructose), lipids, and proteins. The identification of the secretory structures in the sepals of Calolisianthus pedunculatus highlights the importance of anatomical studies in this family. The interpretation of the glandular areas on the calyx of the Helieae species as nectaries has been proven, as well as the confirmation of colleters as common structures in the sepals of Gentianaceae. Besides the taxonomic and phylogenetic importance of nectars and colleters, we highlight the importance of the secretion for the protection of floral buds against dehydration.

Genetic architecture of fruit size and shape variation in cucurbits: a comparative perspective

The Cucurbitaceae family hosts many economically important fruit vegetables (cucurbits) such as cucumber, melon, watermelon, pumpkin/squash, and various gourds. The cucurbits are probably best known for the diverse fruit sizes and shapes, but little is known about their genetic basis and molecular regulation. Here, we reviewed the literature on fruit size (FS), shape (FSI), and fruit weight (FW) QTL identified in cucumber, melon, and watermelon, from which 150 consensus QTL for these traits were inferred. Genome-wide survey of the three cucurbit genomes identified 253 homologs of eight classes of fruit or grain size/weight-related genes cloned in Arabidopsis, tomato, and rice that encode proteins containing the characteristic CNR (cell number regulator), CSR (cell size regulator), CYP78A (cytochrome P450), SUN, OVATE, TRM (TONNEAU1 Recruiting Motif), YABBY, and WOX domains. Alignment of the consensus QTL with candidate gene homologs revealed widespread structure and function conservation of fruit size/shape gene homologs in cucurbits, which was exemplified with the fruit size/shape candidate genes CsSUN25-26-27a and CsTRM5 in cucumber, CmOFP1a in melon, and ClSUN25-26-27a in watermelon. In cucurbits, the andromonoecy (for 1-aminocyclopropane-1-carboxylate synthase) and the carpel number (for CLAVATA3) loci are known to have pleiotropic effects on fruit shape, which may complicate identification of fruit size/shape candidate genes in these regions. The present work illustrates the power of comparative analysis in understanding the genetic architecture of fruit size/shape variation, which may facilitate QTL mapping and cloning for fruit size-related traits in cucurbits. The limitations and perspectives of this approach are also discussed.

Target sequencing reveals genetic diversity, population structure, core-SNP markers, and fruit shape-associated loci in pepper varieties

BACKGROUND

The widely cultivated pepper (Capsicum spp.) is one of the most diverse vegetables; however, little research has focused on characterizing the genetic diversity and relatedness of commercial varieties grown in China. In this study, a panel of 92 perfect single-nucleotide polymorphisms (SNPs) was identified using re-sequencing data from 35 different C. annuum lines. Based on this panel, a Target SNP-seq genotyping method was designed, which combined multiplex amplification of perfect SNPs with Illumina sequencing, to detect polymorphisms across 271 commercial pepper varieties.

RESULTS

The perfect SNPs panel had a high discriminating capacity due to the average value of polymorphism information content, observed heterozygosity, expected heterozygosity, and minor allele frequency, which were 0.31, 0.28, 0.4, and 0.31, respectively. Notably, the studied pepper varieties were morphologically categorized based on fruit shape as blocky-, long horn-, short horn-, and linear-fruited. The long horn-fruited population exhibited the most genetic diversity followed by the short horn-, linear-, and blocky-fruited populations. A set of 35 core SNPs were then used as kompetitive allele-specific PCR (KASPar) markers, another robust genotyping technique for variety identification. Analysis of genetic relatedness using principal component analysis and phylogenetic tree construction indicated that the four fruit shape populations clustered separately with limited overlaps. Based on STRUCTURE clustering, it was possible to divide the varieties into five subpopulations, which correlated with fruit shape. Further, the subpopulations were statistically different according to a randomization test and F_st statistics. Nine loci, located on chromosomes 1, 2, 3, 4, 6, and 12, were identified to be significantly associated with the fruit shape index (p < 0.0001).

CONCLUSIONS

Target SNP-seq developed in this study appears as an efficient power tool to detect the genetic diversity, population relatedness and molecular breeding in pepper. Moreover, this study demonstrates that the genetic structure of Chinese pepper varieties is significantly influenced by breeding programs focused on fruit shape.

Characterizing 3D inflorescence architecture in grapevine using X-ray imaging and advanced morphometrics: implications for understanding cluster density

Inflorescence architecture provides the scaffold on which flowers and fruits develop, and consequently is a primary trait under investigation in many crop systems. Yet the challenge remains to analyse these complex 3D branching structures with appropriate tools. High information content datasets are required to represent the actual structure and facilitate full analysis of both the geometric and the topological features relevant to phenotypic variation in order to clarify evolutionary and developmental inflorescence patterns. We combined advanced imaging (X-ray tomography) and computational approaches (topological and geometric data analysis and structural simulations) to comprehensively characterize grapevine inflorescence architecture (the rachis and all branches without berries) among 10 wild Vitis species. Clustering and correlation analyses revealed unexpected relationships, for example pedicel branch angles were largely independent of other traits. We identified multivariate traits that typified species, which allowed us to classify species with 78.3% accuracy, versus 10% by chance. Twelve traits had strong signals across phylogenetic clades, providing insight into the evolution of inflorescence architecture. We provide an advanced framework to quantify 3D inflorescence and other branched plant structures that can be used to tease apart subtle, heritable features for a better understanding of genetic and environmental effects on plant phenotypes.

Comprehensive analysis of the internal structure and firmness in American cranberry (Vaccinium macrocarpon Ait.) fruit

BACKGROUND

Cranberry (Vaccinium macrocarpon L.) fruit quality traits encompass many properties. Although visual appearance and fruit nutritional constitution have usually been the most important attributes, cranberry textural properties such as firmness have recently gained importance in the industry. Fruit firmness has become a quality standard due to the recent demand increase for sweetened and dried cranberries (SDC), which are currently the most profitable cranberry product. Traditionally, this trait has been measured by the cranberry industry using compression tests; however, it is poorly understood how fruit firmness is influenced by other characteristics.

RESULTS

In this study, we developed a high-throughput computer-vision method to measure the internal structure of cranberry fruit, which may in turn influence cranberry fruit firmness. We measured the internal structure of 16 cranberry cultivars measured over a 40-day period, representing more than 3000 individual fruit evaluated for 10 different traits. The internal structure data paired with fruit firmness values at each evaluation period allowed us to explore the correlations between firmness and internal morphological characteristics.

CONCLUSIONS

Our study highlights the potential use of internal structure and firmness data as a decision-making tool for cranberry processing, especially to determine optimal harvest times and ensure high quality fruit. In particular, this study introduces novel methods to define key parameters of cranberry fruit that have not been characterized in cranberry yet. This project will aid in the future evaluation of cranberry cultivars for in SDC production.

Multivariate analysis reveals phenotypic diversity of Euscaphis japonica population

Fruit traits affect population genetic diversity by affecting seed protection and dispersal strategies, thereby comprising important components of phenotypic variation. Understanding of the phenotypic variation is an indispensable first step for developing breeding strategies. However, little information is known about the genetic variation in E. japonica-a monotypic species with abundant phenotypes that is mainly distributed in southern China. In this study, we evaluated the phenotypic diversity of 67 E. japonica using 23 phenotypic traits. Our results showed that the Shannon-Wiener (I) index of qualitative traits ranged from 0.55 to 1.26, and the color traits had a relatively high I. The average coefficient of variation of compound leaf traits (14.74%) was higher than that of fruit and seed traits (12.77% and 11.47%, respectively). Principal component analysis also showed that compound leaf and fruit traits were important components of total variation. Furthermore, correlation analysis revealed a significant difference in elevation and fruit color, irregular ribs, leaf margin and texture. The F value within populations was smaller than among populations, indicating the variation in phenotypic traits among populations was much greater than within populations. Dehua and Zunyi populations had the highest coefficients of variation, whereas Wenzhou population had the smallest-which may be attributed to habitat destruction. According to Q-type clustering, 67 samples clustered into four groups, with those having similar phenotypes clustering into the same group. In general, leaf and fruit traits had abundant phenotypic diversity, representing the main sources of phenotypic variation. Combined with clustering results and field surveys, this study suggests that the phenotypes of E. japonica are classified into two main categories: The deciduous E. japonica present at high altitudes; and the evergreen E. japonica present at low altitudes. Excavating E. japonica variations provides a theoretical reference for its classification and diversity, and is of great significance for planning genetic resources and establishing conservation strategies.

Mesocarp of Brazil nut (Bertholletia excelsa) as inspiration for new impact resistant materials

Aiming to produce bioinspired impact and puncture resistant materials, the mesocarp of the Brazil nut (Bertholletia excelsa) was characterized. The mesocarp composition was investigated by chemical extraction and its microstructure was analyzed by optical microscopy and microtomography (microCT). A compression test evaluated the force needed to open the mesocarp shell. Shore D hardness testing and nanoindentation measured the local mechanical properties at different length scales. Brazil nut mesocarp has a higher content of lignin (56%) than other nutshells and is mainly composed of sclereids and fibers cells arranged together and not in separated layers as usually found in nature. The mesocarp has an internal and external layer with fibers oriented from peduncle to opercular opening and a middle layer where entangled fibers are latitudinally oriented. To open a Brazil nut mesocarp, compression forces of 10 079  ±  1460 N (parallel to latitudinal section) and 14 785  ±  4050 N (perpendicular to latitudinal section) are needed. Such forces are higher than the forces needed to open most nutshells, if fracture force is normalized by shell thickness. The Shore D hardness test showed that hardness is uniform in the mesocarp, although it is higher in the center of the thickness than close to the inner or outer surface. The cell wall of fibers has a higher reduced modulus than the cell wall of sclereids although they have a similar hardness. These microstructural and mechanical results indicate that Brazil nutshell has great potential as a source for bioinspiration and motivates further studies.

Exploring sub-individual variability: role of ontogeny, abiotic environment and seed-dispersing birds

Within-individual trait variation - otherwise known as sub-individual variation - is an important component of phenotypic variation, with both a genetic and epigenetic basis. We explore its adaptive value and the effects of ontogeny and the environment on sub-individual variability. We conducted a field study to analyse the effects of tree age, soil pH, soil water content and soil nutrients on sub-individual variability in fruit size of hawthorn (Crataegus monogyna) in three sites in northwest Spain. Additionally, we examined how bird-mediated selection influences average and sub-individual variation in fruit size. Results show that average and sub-individual variations in fruit size were related to fitness affecting seed dispersal. Older trees produced larger fruits, but tree age did not affect sub-individual variation in fruit size. Abiotic environmental factors differently affected sub-individual variation and average fruit size. Seed-dispersing birds exerted correlated selection on average and variation in fruit size, favouring trees with larger and less variable fruit size at one site. Our work suggests that the fruit size variation within individual trees, the sub-individual variation, is modified by abiotic environmental factors and, additionally, is an adaptive trait that responds to natural selection.

Cytokinin treatment modifies litchi fruit pericarp anatomy leading to reduced susceptibility to post-harvest pericarp browning

Litchi (Litchi chinensis Sonn.) is a subtropical fruit known for its attractive red pericarp color, semi-translucent white aril and unique flavor and aroma. Rapid post-harvest pericarp browning strictly limits litchi fruit marketing. In the current research, we hypothesized that modification of litchi fruit pericarp anatomy by hormone application may reduce fruit susceptibility to post-harvest pericarp browning. In this context, we hypothesized that cytokinin treatment, known to induce cell division, may yield fruit with thicker pericarp and reduced susceptibility for fruit surface micro-crack formation, water loss and post-harvest pericarp browning. Exogenous cytokinin treatment was applied at different stages along the course of litchi fruit development and the effect on fruit pericarp anatomy, fruit maturation and postharvest pericarp browning was investigated. Interestingly, cytokinin treatment, applied 4 weeks after full female bloom (WFB), during the phase of pericarp cell division, led to mature fruit with thicker pericarp, reduced rate of post-harvest water loss and reduced susceptibility to post-harvest pericarp browning, as compared to non-treated control fruit. Histological sections ascribe the difference in pericarp anatomy to increased cell proliferation in the parenchymatic tissue and the highly-lignified brachysclereid cell layer. In contrast, exogenous cytokinin treatment applied 7 WFB, following the phase of pericarp cell division, significantly increased epidermal-cell proliferation but had no significant effect on overall fruit pericarp thickness and only minor affect on post-harvest water loss or pericarp browning. Interestingly, the late cytokinin treatment also significantly postponed fruit maturation-associated anthocyanin accumulation and chlorophyll degradation, as previously reported, but had no effect on other parameters of fruit maturation, like total soluble sugars and total titratable acids typically modified during aril maturation. In conclusion, exogenous cytokinin treatment at different stages in fruit development differentially modifies litchi fruit pericarp anatomy by induction of cell-type specific cell proliferation. Early cytokinin treatment during the phase of pericarp cell division may prolong litchi fruit storage by reducing fruit susceptibility to post-harvest water loss and pericarp browning.

Phenolic distribution in apple epidermal and outer cortex tissue by multispectral deep-UV autofluorescence cryo-imaging

Phenolic compounds in fruit are involved in responses to biotic and abiotic stresses and are responsible for organoleptic properties. To establish the distribution of these secondary metabolites at the tissue and sub-cellular scales, mapping of fluorescence in apple epidermis and outer cortex tissue in cryogenic condition was performed after deep-UV excitation at 275 nm. Douce Moën and Guillevic cider apple varieties were sampled and frozen after harvest, after 30 days at 4 °C and after 20 days at room temperature. Image analysis of fluorescence emission images acquired between 300 and 650 nm allowed the assignment of fluorescence signals to phenolic compound families based on reference molecules. Emission attributed to monomeric and/or condensed flavanol was localized in whole tissue with major fluorescence in the cuticle region. Hydroxycinnamic acids were found predominantly in the outer cortex and appeared in the cell wall. Fluorescent pigments were mostly found in the epidermis. The distribution of flavanols in the sub-cuticle and phenolic acids in the outer cortex distinguished apple varieties. Storage conditions had no impact on phenolic distribution. The proposed fluorescent imaging and analysis approach enables studies on phenolic distribution in relation to fruit development, biotic/abiotic stress resistance and quality.

Grape berry position affects the diurnal dynamics of its metabolic profile

Solar irradiance and air temperature are characterized by dramatic circadian fluctuations and are known to significantly modulate fruit composition. To date, it remains unclear whether the abrupt, yet predictive, diurnal changes in radiation and temperature prompt direct metabolic turn-over in the fruit. We assessed the role of fruit insolation, air temperature, and source-tissue CO₂ assimilation in the diurnal compositional changes in ripening grape berries. This was performed by comparing the diurnal changes in metabolite profiles of berries positioned such that they experienced (a) contrasting diurnal solar irradiance patterns, and (b) similar irradiance but contrasting diurnal CO₂ assimilation patterns of adjacent leaves. Grape carbon levels increased during the morning and decreased thereafter. Sucrose levels decreased throughout the day and were correlated with air temperature, but not with the diurnal pattern of leaf CO₂ assimilation. Tight correlation between sucrose and glucose-6-phosphate indicated the involvement of photorespiration/glycolysis in sucrose depletion. Amino acids, polyamines, and phenylpropanoids fluctuated diurnally, and were highly responsive to the diurnal insolation pattern of the fruit. Our results fill the knowledge gap regarding the circadian pattern of source-sink assimilate-translocation in grapevine. In addition, they suggest that short-term direct solar exposure of the fruit impacts both its diurnal and nocturnal metabolism.

Proteome and transcriptome analyses reveal key molecular differences between quality parameters of commercial-ripe and tree-ripe fig (Ficus carica L.)

BACKGROUND

Fig fruit are highly perishable at the tree-ripe (TR) stage. Commercial-ripe (CR) fruit, which are harvested before the TR stage for their postharvest transportability and shelf-life advantage, are inferior to TR fruit in size, color and sugar content. The succulent urn-shaped receptacle, serving as the protective structure and edible part of the fruit, determines fruit quality. Quantitative iTRAQ and RNA-Seq were performed to reveal the differential proteomic and transcriptomic traits of the receptacle at the two harvest stages.

RESULTS

We identified 1226 proteins, of which 84 differentially abundant proteins (DAPs) were recruited by criteria of abundance fold-change (FC) ≥1.3 and p < 0.05 in the TR/CR receptacle proteomic analysis. In addition, 2087 differentially expressed genes (DEGs) were screened by ≥2-fold expression change: 1274 were upregulated and 813 were downregulated in the TR vs. CR transcriptomic analysis. Ficin was the most abundant soluble protein in the fig receptacle. Sucrose synthase, sucrose-phosphate synthase and hexokinase were all actively upregulated at both the protein and transcriptional levels. Endoglucanase, expansin, beta-galactosidase, pectin esterase and aquaporins were upregulated from the CR to TR stage at the protein level. In hormonal synthesis and signaling pathways, high protein and transcriptional levels of aminocyclopropane-1-carboxylate oxidase were identified, together with a few diversely expressed ethylene-response factors, indicating the potential leading role of ethylene in the ripening process of fig receptacle, which has been recently reported as a non-climacteric tissue.

CONCLUSIONS

We present the first delineation of intra- and inter-omic changes in the expression of specific proteins and genes of TR vs. CR fig receptacle, providing valuable candidates for further study of fruit-quality formation control and fig cultivar innovation to accommodate market demand.

The establishment of the species-delimits and varietal-identities of the cultivated germplasm of Luffa acutangula and Luffa aegyptiaca in Sri Lanka using morphometric, organoleptic and phylogenetic approaches

Luffa acutangula and L. aegyptiaca are two vegetable species commonly found in South and South East Asia. L. acutangula is widely grown; however, L. aegyptiaca is considered as an underutilized crop. The species delimits, phylogenetic positions, and the varietal identities of L. acutangula and L. aegyptiaca in Sri Lanka are not known. Thus, in the present study, we aimed to establish the species delimits and varietal identities of L. acutangula and L. aegyptiaca varieties grown in Sri Lanka using morphometric, phylogenetic and organoleptic assessments. We assessed five varieties of L. acutangula and three varieties of L. aegyptiaca. The vegetative and reproductive data were collected for the morphometric analysis and DNA sequence polymorphism of the makers rbcL, trnH-psbA and ITS for the phylogenetic analysis. We also conducted an organoleptic assessment based on taste parameters; aroma, bitterness, color, texture, and overall preference using the dishes prepared according to the most common Sri Lankan recipe for Luffa. The variation of the vegetative and reproductive traits grouped L. acutangula varieties into two distinct clusters. The trnH-psbA polymorphism provided the basis for the species delimits of L. acutangula and L. aegyptiaca. The rbcL and ITS polymorphisms provided the basis for the identities of the varieties of L. aegyptiaca and L. acutangula respectively. In the phylogeny, the L. acutangula varieties of Sri Lanka formed a unique clade and the L. aegyptiaca varieties formed a reciprocal monophyletic group in comparison to worldwide L. aegyptiaca reported. The taste parameters aroma, texture, color, and overall preference were significantly different among the Luffa varieties. The L. aegyptiaca varieties received lower preference in the organoleptic assessment. The present study sets the species delimits, phylogenetic positions and the varietal identities of the cultivated germplasm of Luffa and revealed the distinct morphological and organoleptic properties of each variety.

A Multilevel Study of Melon Fruit Reticulation Provides Insight into Skin Ligno-Suberization Hallmarks

The skin of fleshy fruit is typically covered by a thick cuticle. Some fruit species develop different forms of layers directly above their skin. Reticulation, for example, is a specialized suberin-based coating that ornaments some commercially important melon (Cucumis melo) fruit and is an important quality trait. Despite its importance, the structural, molecular, and biochemical features associated with reticulation are not fully understood. Here, we performed a multilevel investigation of structural attributes, chemical composition, and gene expression profiles on a set of reticulated and smooth skin melons. High-resolution microscopy, surface profiling, and histochemical staining assays show that reticulation comprises cells with heavily suberized walls accumulating large amounts of typical suberin monomers, as well as lignified cells localized underneath the specialized suberized cell layer. Reticulated skin was characterized by induced expression of biosynthetic genes acting in the core phenylpropanoid, suberin, lignin, and lignan pathways. Transcripts of genes associated with lipid polymer assembly, cell wall organization, and loosening were highly enriched in reticulated skin tissue. These signatures were exclusive to reticulated structures and absent in both the smooth surfaces observed in between reticulated regions and in the skin of smooth fruit. Our data provide important insights into the molecular and metabolic bases of reticulation and its tight association with skin ligno-suberization during melon fruit development. Moreover, these insights are likely to contribute to melon breeding programs aimed at improving postharvest qualities associated with fleshy fruit surface layers.

Morphology and Molecular Identification of Twelve Commercial Varieties of Kiwifruit

The quality and safety of food are important guarantees for the health and legal rights of consumers. As an important special fruitcrop, there are frequently shoddy practices in the kiwifruit (Actinidia chinensis) market, which harms the interests of consumers. However, there is lack of rapid and accurate identification methods for commercial kiwifruit varieties. Here, twelve common commercial varieties of kiwifruit were morphologically discriminated. DNA barcodes of chloroplast regions psbA-trnH, rbcL, matK, rpoB, rpoC1, ycf1b, trnL and rpl32_trnL(UAG), the nuclear region At103 and intergenic region ITS2 were amplified. Divergences and phylogenetic trees were used to analyze the phylogenetic relationship of these twelve commercial kiwifruit varieties. The results showed that matK, ITS2 and rpl32_trnL(UAG) can be utilized as molecular markers to identify CuiYu, JinYan, HuangJinGuo, ChuanHuangJin, HuaYou, YaTe, XuXiang and HongYang. This provides experimental and practical basis to scientifically resolve kiwifruit-related judicial disputes and legal trials.

Russeting partially restores apple skin permeability to water vapour

The higher water loss of russeted fruit results from the higher permeance of the periderm of the russeted skin as compared to that of the intact cuticle and epidermis. Apple fruit surfaces are often in-parallel composites, comprising areas of intact cuticle (atop a healthy epidermis) adjacent to areas covered by periderm (so-called russet). The occurrence of non-russeting and russeting genotypes makes this species an ideal model to study the barrier properties of its composite skin. The objective was to quantify the water vapour permeances of non-russeted ([Formula: see text]) and russeted fruit skins ([Formula: see text]). Rates of water loss from whole fruit ([Formula: see text]) and excised epidermal skin segments (ES) or peridermal skin segments (PS) were quantified gravimetrically. The [Formula: see text] was larger in russeting than in non-russeting genotypes because [Formula: see text] exceeded [Formula: see text] by about twofold. Also, the [Formula: see text] of russeting genotypes was larger than that of non-russeting genotypes. Generally, [Formula: see text] was more variable than [Formula: see text]. These differences were consistent across seasons and genotypes. The lower [Formula: see text] as compared to [Formula: see text] resulted primarily from the higher wax content of the cuticle of the [Formula: see text]. For non-russeted genotypes, the value of [Formula: see text] was significantly related to the permeance determined on the same intact fruit ([Formula: see text]). Close relationships were also found between the [Formula: see text] calculated from [Formula: see text] determined on the same fruit and the measured [Formula: see text]. For russeting genotypes, the [Formula: see text] or [Formula: see text] were not correlated with [Formula: see text]. The [Formula: see text] calculated from [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] (all determined on an individual-fruit basis) was significantly correlated with the measured [Formula: see text]. Our results demonstrate that the periderm permeance exceeds the cuticle permeance and that permeances of non-russeted surfaces of russeting genotypes exceed those of non-russeting genotypes.

Variability in space and time: contrasting fruit distribution patterns in the deceptive orchid Orchis militaris

In angiosperms, a decrease in fruit production towards the apex of individual inflorescences is usually observed. Orchids are thought to be primarily pollination-limited species, and non-uniform pollination could cause this decrease pattern in several species. Fruit production was investigated in relation to flower position and floral display size in Orchis militaris (Orchidaceae), a deceptive species. Over 2 years, eight populations of O. militaris were studied and fruit position along the inflorescence was recorded. Generalised linear models were performed to examine the effect of population, year, flower position and floral display size on fruit production. The dominant pattern was characterised by a higher fruit set in the middle part of the inflorescence (parabolic pattern). A non-directional pattern of fruit production was also detected in some populations. Within a given population, patterns were generally consistent among years. In one of the two study years and in one of the eight populations specifically, the proximal-to-distal decrease in fruit production was dramatic in plants with a large floral display but weak or absent in small displays. Our study demonstrates the intraspecific diversity of fruit distribution patterns in O. militaris. Non-uniform pollination along the inflorescence is likely to be responsible for the parabolic pattern, while irregular visitation could explain the non-directional pattern of fruit production. Pattern variation among years and between populations could arise from spatiotemporal variation in pollinator assemblages. Resource competition effects could explain the interaction effect between display size and flower position.

ATR-FTIR spectroscopy non-destructively detects damage-induced sour rot infection in whole tomato fruit

ATR-FTIR spectroscopy with subsequent multivariate analysis non-destructively identifies plant-pathogen interactions during disease progression, both directly and indirectly, through alterations in the spectral fingerprint. Plant-environment interactions are essential to understanding crop biology, optimizing crop use, and minimizing loss to ensure food security. Damage-induced pathogen infection of delicate fruit crops such as tomato (Solanum lycopersicum) are therefore important processes related to crop biology and modern horticulture. Fruit epidermis as a first barrier at the plant-environment interface, is specifically involved in environmental interactions and often shows substantial structural and functional changes in response to unfavourable conditions. Methods available to investigate such systems in their native form, however, are limited by often required and destructive sample preparation, or scarce amounts of molecular level information. To explore biochemical changes and evaluate diagnostic potential for damage-induced pathogen infection of cherry tomato (cv. Piccolo) both directly and indirectly, mid-infrared (MIR) spectroscopy was applied in combination with exploratory multivariate analysis. ATR-FTIR fingerprint spectra (1800-900 cm^-1) of healthy, damaged or sour rot-infected tomato fruit were acquired and distinguished using principal component analysis and linear discriminant analysis (PCA-LDA). Main biochemical constituents of healthy tomato fruit epidermis are characterized while multivariate analysis discriminated subtle biochemical changes distinguishing healthy tomato from damaged, early or late sour rot-infected tomato indirectly based solely on changes in the fruit epidermis. Sour rot causing agent Geotrichum candidum was detected directly in vivo and characterized based on spectral features distinct from tomato fruit. Diagnostic potential for indirect pathogen detection based on tomato fruit skin was evaluated using the linear discriminant classifier (PCA-LDC). Exploratory and diagnostic analysis of ATR-FTIR spectra offers biological insights and detection potential for intact plant-pathogen systems as they are found in horticultural industries.

Cretaceous asterid evolution: fruits of Eydeia jerseyensis sp. nov. (Cornales) from the upper Turonian of eastern North America

BACKGROUND AND AIMS

The asterids (>80 000 extant species) appear in the fossil record with considerable diversity near the Turonian-Coniacian boundary (~90 Ma; Late Cretaceous) and are strongly represented in the earliest diverging lineage, Cornales. These early asterid representatives have so far been reported from western North America and eastern Asia. In this study, we characterize a new cornalean taxon based on charcoalified fruits from the upper Turonian of eastern North America, a separate landmass from western North America at the time, and identify early palaeobiogeographical patterns of Cornales during the Cretaceous.

METHODS

Fossils were studied and imaged using scanning electron microscopy and micro-computed tomography (micro-CT) scanning. To assess the systematic affinities of the fossils, phylogenetic analyses were conducted using maximum parsimony.

KEY RESULTS

The charcoalified fruits are represented by tri-locular woody endocarps with dorsal apically opening germination valves. Three septa intersect to form a robust central axis. Endocarp ground tissue consists of two zones: an outer endocarp composed of isodiametric sclereids and an inner endocarp containing circum-locular fibres. Central vasculature is absent; however, there are several small vascular bundles scattered within the septa. Phylogenetic analysis places the new taxon within the extinct genus Eydeia.

DISCUSSION

Thick-walled endocarps with apically opening germination valves, no central vascular bundle and one seed per locule are indicative of the order Cornales. Comparative analysis suggests that the fossils represent a new species, Eydeia jerseyensis sp. nov. This new taxon is the first evidence of Cornales in eastern North America during the Cretaceous and provides insights into the palaeobiogeography and initial diversification of the order.

Classification of fruit trichomes in cucumber and effects of plant hormones on type II fruit trichome development

Cucumber fruit trichomes could be classified into eight types; all of them are multicellular with complex and different developmental processes as compared with unicellular trichomes in other plants. The fruit trichomes or fruit spines of cucumber, Cucumis sativus L., are highly specialized structures originating from epidermal cells with diverse morphology, which grow perpendicular to the fruit surface. To understand the underlying molecular mechanisms of fruit trichome development, in this study, we conducted morphological characterization and classification of cucumber fruit trichomes and their developmental processes. We examined the fruit trichomes among 200 cucumber varieties, which could be classified into eight morphologically distinct types (I-VIII). Investigation of the organogenesis of the eight types of trichomes revealed two main developmental patterns. The development of glandular trichomes had multiple stages including initiation and expansion of the trichome precursor cell protuberating out of the epidermal surface, followed by periclinal bipartition to two cells (top and bottom) which later formed the head region and the stalk, respectively, through subsequent cell divisions. The non-glandular trichome development started with the expansion of the precursor cell perpendicularly to the epidermal plane followed by cell periclinal division to form a stalk comprising of some rectangle cells and a pointed apex cell. The base cell then started anticlinal bipartition to two cells, which then underwent many cell divisions to form a multicellular spherical structure. In addition, phytohormones as environmental cues were closely related to trichome development. We found that GA and BAP were capable of increasing trichome number per fruit with distinct effects under different concentrations.

Molecular basis of cucumber fruit domestication

Cucumber (Cucumis sativus L.) is an economically important vegetable crop that is cultivated worldwide. Compared to the wild ancestor bearing small, bitter and seedy fruit, domesticated cucumbers exhibit significant variation in fruit appearance, size and flavor. Understanding the molecular basis of domestication related traits can provide insights into fruit evolution and make crop breeding more efficient. Here we review recent advances in relating to the genetic basis of fruit morphological traits (femaleness, fruit spine, wart, size, color and carpel development) and organoleptic features (bitterness) during cucumber domestication.