Fruit Peduncle Research Articles

Effects of an Auxin and a brassinosteroid on physical, chemical and biochemical attributes of ‘Galaxy’ apples

ABSTRACT: The aim of this study was to study the effect of the auxin naphthalene acetic acid (NAA) and the brassinosteroid 28-homocastasterone (28-HCS) applied every 15 days (harvest 2015/16) or every 21 days (harvest 2016/17) after full bloom, on the physical, chemical and biochemical attributes of the ‘Galaxy’ apples. The study was performed at a commercial orchard at Vacaria county, Rio Grande do Sul State, Brazil. The following treatments were applied: water (control), NAA (0.1%), 28-HCS (10‒6 M) and NAA (0.1%) + 28-HCS (10‒6 M). For this purpose, 300 μL of the plant growth regulator solutions were applied to the fruit peduncles. Fruits treated with NAA every 21 days presented higher starch-iodine index and lower total soluble solids (TSS), titratable acidity (TA), lightness index (L) and hue angle (h°) than 28-HCS-treated fruits. Fruits treated every 15 days with NAA presented reduced skin rupture force (SRF), total antioxidant activities (TAA) of the skin and flesh, and hydrogen peroxide content compared to the control fruits. In addition, NAA application every 15 and 21 days resulted in increased anthocyanin content in the skin. Application of NAA + 28-HCS reduced superoxide dismutase activity. 28-HCS applications increased TSS, color attributes (C and h°) of the skin, total antioxidant activity of the skin and flesh and peroxidase activity compared to control fruits. These results are expected to help to understand how plant growth regulators affect apple quality. In addition, results described here are also expected to help on the development of strategies to reduce post harvest losses and to increase fruit shelf life.

The change in microstructure of petioles and peduncles and transporter gene expression by potassium influences the distribution of nutrients and sugars in pear leaves and fruit

Potassium (K) is one of the most important mineral nutrients required for fruit growth and development and is known as a ‘quality element’. To investigate the role of K in more detail, we performed experiments in which seven-year-old pot-grown ‘Huangguan’ pear trees were treated with three levels of K (0, 0.4, or 0.8 g K2O kg−1 soil). K supply improved the development of vascular bundles in pear petioles and fruit peduncles and enhanced expression of genes involved in nutrients and sugar transport. Different from K and calcium (Ca), magnesium (Mg) concentrations in the leaves, petioles, and fruit peduncles were significantly higher under low K but lower under high K. However, the concentrations of K, Ca, and Mg in fruit all increased as more K was applied. Correspondingly, the expression of leaf Mg transporters (MRS2-1 and MRS2-3) increased under low K, indicating that Mg had an obvious compensation effect on K, while their expression decreased under medium and high K, showing that K had an obvious antagonistic effect on Mg. Except for NIPA2, the expressions of fruit K, Ca, and Mg transporters increased under high K, implying a synergistic effect among them in fruit. The concentration of sorbitol, sucrose, and total sugar in leaves and fruit at maturity significantly increased in response to the supply of K. The increase in sugar concentration was closely related to the up-regulated expression of sucrose transporter (SUT) and sorbitol transporter (SOT) genes. Together, these effects may promote the transport of nutrients and sugar from sources (leaves) to sinks (fruit) and increase the accumulation of sugar in the fruit.

Harmonic stress analysis on Coffea arábica L. var. Colombia fruits in order to stimulate the selective detachment: A finite element analysis

This study shows a finite element harmonic stress analysis to evaluate the stress performance at the pedicel interface of a fruit–peduncle system of Coffea arábica L. var. Colombia plants. The aim was to study detachment of fruits subjected to mechanical vibrations. A model of the coffee fruit–peduncle system is designed computationally to reproduce its topology in all ripening stages using a proposed numerical procedure. Young’s modulus, Poisson ratio, and density were adjusted using analytical models for all ripening stages. The glomerulus of three fruits in different ripening stages was proposed and these were combined in four groups. Based on a detachment model, it was verified which fruit was detached first when a chirp force signal was applied on each glomerulus. Results indicated that dynamic excitations applied in between 130 to 150 Hz detached only ripe fruits, since fruits that were in other ripening stages were not stimulated until detachment in that bandwidth.

Genetic Analysis and QTL Mapping of Fruit Peduncle Length in Cucumber (Cucumis sativus L.).

Mechanized harvesting of cucumbers offers significant advantages compared to manual labor as both shortages and costs of labor increase. However the efficient use of machines depends on breeding plants with longer peduncles, but the genetic and molecular basis of fruit peduncle development in cucumber is not well understood. In this study, F2 populations were developed from a cross between two inbred lines, 1101 with a long peduncle and 1694 with a short peduncle. These were grown at two field sites, Hainan, with a tropical marine climate, in December 2014, and Beijing, with a warm temperate climate, in May 2015. Electron microscope examination of the pith cells in the peduncles of the two parental lines showed that line 1101 had significantly greater numbers of smaller cells compared to line 1694. The inheritance of cucumber fruit peduncle length (FPL) was investigated by the mixed major gene and polygene inheritance model. Genetic analysis indicated that FPL in cucumber is quantitatively inherited and controlled by one additive major gene and additive-dominant polygenes (D-2 model). A total of 1460 pairs of SSR (simple sequence repeat) primers were analyzed to identify quantitative trait loci (QTLs). Two similar genetic maps with 78 SSR markers which covered 720.6 cM in seven linkage groups were constructed based on two F2 populations. QTL analysis from the data collected at the two field sites showed that there are two minor QTLs on chromosome 1, named qfpl1.1 and qfpl1.2, and one major QTL on chromosome 6, named qfpl6.1. The marker UW021226, which was the closest one to qfpl6.1, had an accuracy rate of 79.0% when tested against plants selected from populations of the two parents. The results from this study provide insights into the inheritance and molecular mechanism of the variation of FPL in cucumber, and further research will be carried out to fine map qfpl6.1 to develop more accurate markers for MAS breeding.

Field test of different end-effectors for robotic harvesting of sweet-pepper

This paper focusses on field experiments with two different types of endeffectors for robotic harvesting of sweet-pepper fruits. One of the major issues is to reach, grasp and detach the fruit efficiently, without damaging it, while avoiding obstacles in the environment. End-effectors for harvesting fruit must be able to adapt to different fruit sizes and geometries. Two types of end-effectors were designed and realized. The first one had four fingers which utilized the Ray effect to grip the fruit. A scissor-like cut mechanism on top of the fingers was used to cut through the fruit peduncle. The second, a lip-type end-effector first stabilized the fruit using a suction cup after which two rings enclosed and cut the peduncle with a circular blade integrated in the upper lip. Both end-effectors had integrated miniature cameras with a LED illumination system: one Time of Flight camera and the other a colour camera. To study the performance of the end-effectors a number of harvesting experiments were performed in commercial sweet-pepper greenhouses. Special attention was paid to the following aspects: positioning at the target fruit, separation of the fruit from the plant, fruit damage, leaf damage and plant stem damage. Both end-effector designs had their strengths and weaknesses. The Fin ray type end-effector harvested a maximum of 80% of the fruits on the plant, the lip-type end-effector a maximum of 76% of the fruits. In none of the experiments more than 64% of the fruit could be harvested without fruit damage.

TEJIDOS ALTERNATIVOS AL FOLIAR PARA EVALUAR LA RESPUESTA A LA FERTILIZACIÓN CON ZN O B EN AGUACATE HASS

Las deficiencias de zinc (Zn) o boro (B) en frutos y hojas de aguacate (Persea americana Mill.) cv. Hass son comunes en la región productora del estado de Nayarit, México. El seguimiento de la concentración foliar de estos micronutrimentos en respuesta a la fertilización no siempre proporciona un diagnóstico adecuado. El objetivo de esta investigación fue evaluar el efecto de la fertilización al suelo con Zn o B sobre la concentración de estos nutrimentos en el tejido de diferentes estructuras de la planta de aguacate Hass. El estudio se realizó en un huerto comercial de Hass cultivado sin riego en clima semicálido subhúmedo de Tepic, Nayarit. Los tratamientos fueron aplicados al suelo, anualmente del año 2001 al 2005, durante la estación lluviosa (julio y septiembre) y fueron (g por árbol por año): (T-1) dos aplicaciones de 750 g ZnSO4 (35.5 % Zn); (T-2) dos aplicaciones de 29.5 g Boronat® (32 % B); (T-3) testigo, sin aplicación de Zn o B. Los tejidos muestreados fueron: inflorescencias en estado “coliflor”, inflorescencia completa en antesis, flores en antesis, raquis de la inflorescencia en antesis, pedúnculo + pedicelo del fruto en madurez fisiológica, pulpa del fruto y hojas del flujo vegetativo de invierno de seis meses de edad. Los tejidos que mejor reflejaron la respuesta a la fertilización con Zn fueron el raquis de inflorescencias en antesis y la pulpa del fruto en madurez fisiológica. En el caso del B lo fueron las inflorescencias completas en antesis y el pedúnculo + pedicelo del fruto en madurez fisiológica.

Tree water status influences fruit splitting in Citrus

Fruit splitting or cracking is a major physiological disorder in fruit trees markedly influenced by environmental conditions, but conclusive data still are required to provide a definite explanation and preventive measures. Changes in climatic conditions critically influence fruit splitting incidence. We studied plant-soil-ambient water relations in splitting-prone citrus grown under 4 contrasting environmental conditions (climate type and soil), in Spain and Uruguay, over a six years period. Automatic trunk and fruit diameter measurements (trunk and fruit growth rate and maximum daily trunk shrinkage), which are a tree water status indicator, together with factors modifying the tree and fruit water relationship (temperature, ET, rainfall, soil texture, soil moisture, rootstock and xylem anatomy) were studied and correlated with splitting.A close fruit splitting and soil texture relationship was found, inversely correlated with clay and silt percentages, and positively with those for sand. Under 85%-sand soil conditions, slight changes in soil moisture due to fluctuations in temperature, ET, or rainfall changed trunk and fruit growth rate patterns during few hours and induced splitting. Splitting incidence was higher in trees with larger xylem vessels in the fruit peduncle due to rootstock (‘Carrizo’ and ‘C-35’ citrange being higher than ‘FA-5’, ‘Cleopatra’ and Poncirus trifoliata). Finally, reducing the frequency of irrigation by half increased midday canopy temperatures (∼5°C) and splitting (+15%). We conclude that irregularities in the tree water status, due to interactions among soil moisture, rootstock and climatic conditions, leads to a number of substantial changes in fruit growth rate increasing the incidence of fruit splitting.

Enhancement of storage quality and antioxidant capacity of harvested sweet cherry fruit by immersion with β-aminobutyric acid

Freshly harvested sweet cherry fruit were immersed with 30mmolL−1 β-aminobutyric acid (BABA) for 10min and then stored at 20°C for 5 d to investigate the effect of BABA on quality and antioxidant activity. The results showed that BABA-treated cherries had lower respiration rates and weight loss and higher levels of titratable acidity, total phenolics, ascorbic acid, fructose, glucose, sucrose, malic, citric and succinic acids compared with that in control fruit. BABA treatment inhibited the decrease of L* value of fruit pericarp and chlorophyll contents of fruit peduncles. BABA enhanced the antioxidant enzyme activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) throughout the storage period. In addition, BABA-treated fruit exhibited higher levels of antioxidant activity as measured by the scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide and hydroxyl radicals, and by the reducing power test compared to the control. These results indicate that postharvest application of BABA immersion can improve the organoleptic and nutritive qualities and enhance the antioxidant capacity of harvested sweet cherry fruit.

Involvement of abscisic acid in postharvest water-deficit stress associated with the accumulation of anthocyanins in strawberry fruit

Fruits are prone to suffer water-deficit stress and accelerated senescence after harvest. To understand the effect of postharvest water-deficit on the senescence progress of strawberry fruit, fruit peduncles were dipped into water or abscisic acid solution and stored at 20°C with 50% relative humidity in the dark. The results showed that detached fruit without water supply through the peduncles suffered serious water-deficit stress with great weight loss and low moisture content. However, fruit absorbing water through their peduncles successfully avoided the water-deficit stress with a slight change of weight loss and moisture content. Water-deficit significantly promoted anthocyanin levels with increased PAL, C4H and DFR activities. The expressions of transcriptional factors that regulate anthocyanin biosynthesis (FaMYB1, FabHLH3 and FaTTG1) were also up-regulated under water-deficit stress. Meanwhile, stress elevated the abscisic acid level as well as FaNCED1 and FaASR expression in strawberry fruit. Furthermore, exogenous ABA application exhibited the similar features with water-deficit stress. These results suggested that postharvest water-deficit would accelerate anthocyanin accumulation in strawberry fruit and that abscisic acid may play a role in the response to water-deficit stress.

Multi-scale simulation of plant stem reinforcement by brachysclereids: A case study in apple fruit peduncles.

Sclereid formation in addition to or in gaps of fragmented fibre rings is common in dicotyledonous plant stems. Whether this sclereid formation is force-triggered remains open so far. In fruit peduncles of several Malus species as modified plant stems, for example, the persistent fibre ring is displaced to the centre by formation of cortex parenchyma during growth. Parenchyma cells subsequently differentiate into an additional layer of brachysclereids, previously interpreted as an adaptation to continuously rising fruit loads. The present study pursues a multi-scale numerical modelling approach, to verify the important effect for different cellular architectures in both sclerenchyma categories on the stiffness of these tissues and the entire peduncle. First, different material properties are simulated analogue to plant tissues on the basis of three cell types. A regular three-dimensional and a random Voronoi microstructure combined with various mechanical cell wall parameters are applied. Using homogenisation simulations based on HILL's principle, numerical calculations predict a lower effective homogenised tissue stiffness of isodiametric brachysclereids compared to those of fibres, confirming experimentally obtained data from Malus fruit peduncles. Furthermore, a curved peduncle model with a complex arrangement of different material layers is generated. Diverse material sets are tested under three representative loadings, using an adaptive diffuse domain approach (AMDiS). The model explains the function of sclereids as considerable contributors to the stiffness against bending and tensile deformations, as well as torsion, especially in consequence of superimposed load conditions in the case of a curved plant stem.

Planteose is a major sugar translocated in Actinidia arguta ‘Hortgem Tahi’

Planteose, an unusual trisaccharide with galactose attached to the fructose moiety of sucrose, is a major carbohydrate present in Actinidia arguta ‘Hortgem Tahi’ leaves. The aim of this study was to investigate whether planteose was transported in the phloem of ‘Hortgem Tahi’ vines by 14C labelling of recently fixed photosynthate in leaves and measuring the soluble carbohydrate content of phloem exudates. 14C movement was monitored within the vine either non-invasively, detecting Bremsstrahlung radiation or by destructive sampling. Phloem soluble carbohydrate content was examined by EDTA-facilitated exudation from mature leaf petioles and developing fruit peduncles. Bremsstrahlung radiation detection showed that export from the radiolabelled leaf to the peduncle of the subtending fruit or to roots increased rapidly in the late afternoon and evening. During this period of peak export, planteose was present in the phloem exudate from both leaf petioles and fruit peduncles in equal or greater quantities than sucrose. Radiolabelled planteose and sucrose were also both found moving along the shoot away from a radiolabelled leaf. By contrast, in the fruit planteose represented only 2% of the soluble carbohydrate compared with 14% for sucrose. However, the specific activity of 14C was five times higher for planteose than for sucrose, indicating that planteose is quickly metabolised in the fruit. This is the first reported finding of planteose in phloem exudates from the leaf petioles or fruit peduncles in any plant species and indicates planteose is transported in ‘Hortgem Tahi’ vines.

Lasiodiplodia pseudotheobromae causes pedicel and peduncle discolouration of grapes in China

A botryosphaeriaceous taxon causing fruit peduncle and pedicel discolouration was found infecting grapevines in Hubei and Jiangsu Provinces in China. Morphological and phylogenetic analyses showed the taxon to be Lasiodiplodia pseudotheobromae. Pathogenicity testing and Koch’s postulates proved that Lasiodiplodia pseudotheobromae caused fruit peduncle and pedicel discolouration on grape fruit clusters. This is the first report of this fungus causing grapevine fruit peduncle and pedicel discolouration worldwide.

Nuphar carlquistiisp. nov. (Nymphaeaceae): A Water Lily from the Latest Early Eocene, Republic, Washington

Premise of research. Fossil remains of a water lily, Nuphar carlquistii DeVore, Taylor & Pigg sp. nov. (Nymphaeaceae), are described from the latest early Eocene Republic flora of north-central Washington. Specimens include several fruits, one with in situ seeds, others with remnants of stamens and stamen attachment scars, and dispersed seeds found both within a mucilaginous dispersal matrix and separately. Associated structures, including a stigmatic disk, isolated tepals, and several rhizome segments bearing nested clusters of roots and leaf scars, are included in N. cf. carlquistii.Methodology. Fossils preserved in a lacustrine shale were dégaged to reveal details, photographed with LM, and compared morphologically with extant material of related plants.Pivotal results. The study documents the most complete fossil Nuphar known to date. The combination of multiple organs, including fruits, seeds, stamens, and rhizomes with leaf scars and clustered root scars, demonstrates that Eocene Nuphar had vegetative morphology and dispersal methods comparable to those of today. The fossil fruits share morphological features with extant members of section Astylus, establishing the presence of this New World lineage in the latest early Eocene Republic flora in northwestern North America. One specimen, a short rhizome fragment with attached roots that was previously attributed informally to Ensete (Musaceae), is shown to belong to this genus, underscoring the need for complete study of fossils prior to their use as climatic indicators.Conclusions. Nuphar carlquistii is rare among fossil remains of water lilies in having multiple reproductive structures present, including fruit peduncles, characteristic laminate anthers, seed masses in several stages of dispersal, and individual seeds. Associated Nuphar rhizomes with attached roots, tepals, and a stigmatic disk are assigned to N. cf. carlquistii and interpreted as representing the same plant. The presence of N. carlquistii in the Republic flora demonstrates that Nuphar section Astylus had established its present-day structure, plant habit, mode of seed dispersal, and aquatic niche by the early Eocene in the Okanogan Highlands of northwestern North America.

Morphological Analyses of theMecardonia acuminata(Plantaginaceae) Species Complex in the Southeastern USA

The Mecardonia acuminata complex is a classic example of a widespread endemic species in the southeastern US. Morphological variations in the complex resulted in the classification of at least three varieties or subspecies for the species by previous botanists. However, the distributions and diagnostic features of two of the subspecies, peninsularis and microphylla, are unclear due to shared morphological features and widespread distribution of the subspecies acuminata. The present study involved examination and biostatistical analyses of 3 vegetative and 5 reproductive characters that were known to serve as diagnostic features of 1 or more taxa of the species. Results of the study indicate that subspecies peninsularis can be distinguished by its ascending peduncle angle of suspension, diffuse basal branching habit (dendriform at base) of the shoot and small leaves, especially in the southern ranges of the complex. Subspecies microphylla can be distinguished based on its short (<20 mm) fruit peduncles and divaricate peduncle angle of suspension. Subspecies acuminata comprises individuals with divaricate peduncle angle of suspension and long fruit peduncles (>20 mm). Subspecies acuminata was also observed to comprise many individuals that were intermediates of 2 or 3 subspecies. Discriminant function analyses on longitude, latitude, and biogeography as well as Wilks' lambda estimates suggest moderate to low clinal variation and a much broader historical range distribution of subspecies peninuslaris. The morphological variations in the species complex may be due to secondary contact with ongoing integration into subspecies acuminata.

First report of invasive mealybug Phenacoccus solenopsis Tinsley infesting cashew from Goa, India

The solenopsis mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae) has emerged as an aggressive pest on a wide range of host plants in many countries. Mealybug demes were found on young tender leaves, twigs, inflorescence panicles and fruit peduncles of cashew Anacardium occidentale L. (Family: Anacardiaceae). Drying and curling of inflorescences, tender leaves and twigs were observed due to sucking of sap or saliva injection by nymphs and adults of mealybugs. The mealybugs were identified as Phenacoccus solenopsis Tinsley. The peak infestation of 20.73 mealybugs/ 5 cm twig was recorded in the months of April and May during 2012. The endoparasitoid Aenasius bambawalei Hayat (Hymenoptera: Encyrtidae) was also recorded from mummies of P. solenopsis. This is the first report of P. solenopsis infestation on cashew, which may emerge as a sporadic pest of A. occidentale in India.

Biodiversity and indigenous management of the endangered non-toxic germplasm of Jatropha curcas L. in the Totonacapan (Mexico), and the implications for its conservation

Mexico is a center of diversity of Jatropha curcas. Worldwide there are two groups of germplasm, the toxic and the non-toxic, and most of the biofuels programs are based on toxic germplasm. In the mountains of the Totonacapan (Mexico), non-toxic genotypes have been cultivated for human food from ancient times, and now they are in serious risk of being lost because of the "biofuel program'', as well as the ethnobotanical knowledge about this germplasm in the Totonaca culture. The starting hypothesis is that this ethnobotanical knowledge must be related with a high biodiversity of the germplasm of this crop, which is necessary to preserve to avoid genetic erosion. The objective of the work was to assess the biodiversity of the native germplasm using morphological traits, and to analyse socio-economic aspects related with the ethnobotany of this germplasm, to design strategies for the conservation of the germplasm and of the culture linked to it. Other specific objective was to select morphological variables highly discriminant and easy-to-measure, for the characterization of this crop. We selected eight morphological descriptors as the most discriminant, related with the leaves: Length and width of the blade, and length of the petiole; and the fruit: weight, length, diameter, length of the peduncle, and number of fruits per bunch. On the basis of the principal component analysis and canonical discriminant analysis of the morphological data, it was possible to identify as different germplasm pools the six locations sampled, in spite of their proximity, confirming the starting hypothesis that there is high biodiversity of this crop in the region. The pools from Camocuautla and Tuzamapan were the most similar between them, with small fruits and a low number of teeth in the leaves. The germplasm form Jonotla showed also small fruits, but small leaves and a short petiole. Tetelilla's germplasm showed a high number of teeth in the leaves, big fruits and leaves, and long petiole. The accessions from Ecatlan showed big fruits, low number of fruits per bunch and short fruit's peduncle, with small leaves and a short petiole. The differential traits of the accession from Zozocolco were a high number of fruits per bunch and a long fruit's peduncle. Unlike what happened with the germplasm, the socio-economic profile of the farmers did not follow a geographical pattern. Facing the scenario of establishment of the "biofuel program'' in the region, we proposed an on farm conservation strategy consisting in the exclusive use of local nontoxic germplasm, which will need the involvement of all the stakeholders, and in special of the local plant nurseries. As this is difficult to achieve, the ex situ conservation has been proposed as an emergency action. Even if the genetic erosion is stopped, it is necessary to develop other companion measures to avoid the loss of the knowledge about the ancestral uses of this crop, as the farmers could prefer to sell the crop for the industry, instead of use at least a part of it for their own food.

Ontogenetic tissue modification in Malus fruit peduncles: the role of sclereids

Apple (Malus) fruit peduncles are highly modified stems with limited secondary growth because fruit ripening lasts only one season. They must reliably connect rather heavy fruits to the branch and cope with increasing fruit weight, which induces dynamic stresses under oscillating wind loads. This study focuses on tissue modification of these small, exposed structures during fruit development. A combination of microscopic, static and dynamic mechanical tests, as well as Raman spectroscopy, was used to study structure-function relationships in peduncles of one cultivar and 12 wild species, representatively chosen from all sections of the genus Malus. Tissue differentiation and ontogenetic changes in mechanical properties of Malus peduncles were observed throughout one growing season and after successive removal of tissues. Unlike in regular stems, the vascular cambium produces mainly phloem during secondary growth. Hence, in addition to a reduced xylem, all species developed a centrally arranged sclerenchyma ring composed of fibres and brachysclereids. Based on differences in cell-wall thickness, and proportions and arrangement of sclereids, two types of peduncle construction could be distinguished. Fibres provide an increased maximum tensile strength and contribute most to the overall axial rigidity of the peduncles. Sclereids contribute insignificantly to peduncle strength; however, despite being shown to have a lower elastic modulus than fibres, they are the most effective tissue in stiffening peduncles against bending. The experimental data revealed that sclereids originating from cortical parenchyma act as 'accessory' cells to enhance proportions of sclerenchyma during secondary growth in peduncles. The mechanism can be interpreted as an adaptation to continuously increasing fruit loads. Under oscillating longitudinal stresses, sclereids may be regarded as regulating elements between maintenance of stiffness and viscous damping, the latter property being attributed to the cortical parenchyma.

Analysis of Boron and B-pectin Complex Content in the Abscission Zone during Floral and Fruit Abscission in Tobacco (Nicotiana tabacum)

After fruit development has been triggered by pollination, the abscission zone (AZ) in the pedicel strengthens its adhesion to retain the fruit. In tobacco, unpollinated flowers are shed from the AZ, while enlargement of the same tissue occurs in pollinated flowers. The abscission rate depends on effective pollination. In this study, we focused on pectin and boron (B) distribution and their functions in the AZ. B is an essential micronutrient that forms cross-links in pectin, which are important for organ differentiation and maturation. B content and the formation rate of the borate-ester cross-linked rhamnogalacturonan II dimer (dRG-II-B) were measured in tobacco. Expression of NtGUT1, which is important for the formation of dRG-II-B, and the B transporter NtNIP3;1 were analyzed in the peduncle and AZ. To determine B content and dRG-II-B formation rate, the following samples were collected: bud peduncle, bud AZ, fruit peduncle, fruit AZ, and flower AZs, which were treated to prevent pollination or were artificially pollinated. Samples treated in HNO3 were assayed for total B content with ICP-MS. Endo-polygalacturonase (EPG)-treated alcohol-insoluble residues were assayed for formation rates of dRG-II-B with HPLC. Although there was more total B in fruit AZs than in branches, no differences in total B, water-soluble B, and B relevant to cross-linking with RG-II were found between buds and fruits. The formation rates of dRG-II-B were also the same in peduncles and AZs in both buds and fruits. These have the same characteristics of variation with or without pollination. Expression of both NtGUT1 and NtNIP3;1 was highest in AZs of flowers before opening, however, expression of NtGUT1 in flower AZs without pollination was not significantly different from after artificial pollination. These results suggest that the presence of relatively large amounts of B and pectin is important in structural enhancement of AZs after anthesis, but is not related to abscission with or without pollination.

Assessment of quality‐assured Tarocco orange fruit sorting rules by combined physicochemical and sensory testing

The aim of this study was to extract a sorting rule for Tarocco orange fruit from several physicochemical and sensory tests performed on a marketable lot of 399 Tarocco orange fruits. The elastic tension at 5% strain (T₅ ) was found to be linearly correlated (r = 0.65) with the Magness-Taylor (MT) index. Thus T₅ was regarded as a non-destructive parameter quantifying fruit firmness and used to categorise the aforementioned lot in three different firmness classes, high (HF), medium (MF) and low (LF). Only the MT index, fruit rind thickness near the fruit peduncle, lightness coefficient and yellow/blue hue component of the orange flesh, as well as total soluble solid content, confirmed the validity of this discrimination at the significance level of 5%. Sensory professionals recognised the greater compactness (7 ± 2) but lower ease of peeling (4 ± 2) and segment separation (4 ± 2) of the HF oranges with respect to the corresponding sensory attributes of orange fruits grouped in the MF and LF classes. To limit the costly rejection of Tarocco orange fruit considered too soft, especially after long-term shipping, it would be reasonable to select only fruits characterised by a compressive force or tension at 5% strain in the range 23-41 N or 300-540 N m⁻¹ respectively.

Colonization of Citrus Seed Coats by ‘CandidatusLiberibacter asiaticus’: Implications for Seed Transmission of the Bacterium

Huanglongbing is an economically damaging disease of citrus associated with infection by 'Candidatus Liberibacter asiaticus'. Transmission of the organism via infection of seeds has not been demonstrated but is a concern since some citrus varieties, particularly those used as rootstocks in commercial plantings are propagated from seed. We compared the incidence of detection of 'Ca. Liberibacter asiaticus' DNA in individual fruit peduncles, seed coats, seeds, and in germinated seedlings from 'Sanguenelli' sweet orange and 'Conners' grapefruit fruits sampled from infected trees. Using real-time quantitative PCR (qPCR) we detected pathogen DNA in nucleic acid extracts of 36 and 100% of peduncles from 'Sanguenelli' and from 'Conners' fruits, respectively. We also detected pathogen DNA in extracts of 37 and 98% of seed coats and in 1.6 and 4% of extracts from the corresponding seeds of 'Sanguenelli' and 'Conners', respectively. Small amounts of pathogen DNA were detected in 10% of 'Sanguenelli' seedlings grown in the greenhouse, but in none of 204 extracts from 'Conners' seedlings. Pathogen DNA was detected in 4.9% and in 89% of seed coats peeled from seeds of 'Sanguenelli' and 'Conners' which were germinated on agar, and in 5% of 'Sanguenelli' but in none of 164 'Conners' seedlings which grew from these seeds on agar. No pathogen DNA was detected in 'Ridge Pineapple' tissue at 3 months post-grafting onto 'Sanguenelli' seedlings, even when pathogen DNA had been detected initially in the 'Sanguenelli' seedling. Though the apparent colonization of 'Conners' seeds was more extensive and nearly uniform compared with 'Sanguenelli' seeds, no pathogen DNA was detected in 'Conners' seedlings grown from these seeds. For either variety, no association was established between the presence of pathogen DNA in fruit peduncles and seed coats and in seedlings.