Side Of Leaf Research Articles

Manipulation of Phototactic Responses by Two-Spotted Spider Mites to Improve Performance of Miticides

Insight into phototactic responses by herbivorous crop pests may be used to manipulate their vertical distribution in crop canopies. Here, we tested the hypothesis that the deployment of specific light sources elicits positive or negative phototactic responses and can be used to enhance performance of miticide applications. We characterized movement responses by two-spotted spider mites (Tetranychus urticae) (spider mites) to seven light sources [ambient (control), UV-C, UV-B, blue, red, white, and near-infrared (NIR)] under experimental conditions. Separate experiments were conducted with/without the presence of a shelter. An analytical approach based on linear regression coefficients (intercept and slope) from observations in ascending order was used. Linear regression coefficients from UV-B indicated significantly negative phototactic bio-response. We examined settlement of spider mites when exposed to 11 light source configurations and with adaxial leaf sides facing either upwards or downwards. This experiment revealed strong positive and negative phototactic bio-responses to blue light and UV-B light, respectively. As a validation experiment, soybean plants were experimentally infested with spider mites and subjected to one of the following three treatments: (1) no treatment (control), (2) miticide [pyrethrins and Beauveria bassiana (BotaniGard Maxx)] only, and (3) a combination of blue and UV-B for 10 min immediately prior to miticide application. Integration of miticide application with prior deployment of blue and UV-B lights significantly increased the performance of miticide application. Results from this study supported the hypothesis. As a pest management approach, the integration of blue light (to elicit positive phototactic response) and UV-B (to elicit negative phototactic response) is believed to be of particular relevance to organic crop producers and/or to producers of crops for which limited numbers of miticides are registered.

Regulation mechanism of droplets wetting on banana leaf surface and its dynamic contact angle wetting model

The effective wetting and deposition of pesticide droplets on the leaf surface significantly affect the control of pests and diseases, and its mainly affected by the leaf surface properties and pesticide formulation properties. This article aims to investigate the wettability regulation mechanism and dynamic wetting properties of banana leaves, in order to intelligently design appropriate pesticide formulations. The micro-morphology of the banana leaves exhibits a micro-nano dual-scale structure with different microstructures and roughness on the adaxial side and abaxial side. Correspondingly, the wettability on the adaxial side of the banana leaf with higher roughness (Rq = 71.1 nm) is always better than that on the abaxial side (Rq = 42.5 nm). The droplet contact performance of droplets exhibits a strong concentration dependence of surfactants, which regulate the inter-species differences in the wettability of different pesticide formulations on both sides. Besides, the dynamic wetting process of pesticide droplets exhibits strong time dependence, by using a time series method to establish an AR(2) model, precise simulation and prediction of the contact angle changes on the adaxial side (R2 = 0.9560) and abaxial side (R2 = 0.8903) during the dynamic wetting process were achieved. The dynamic wetting model provides new insights into the spreading and deposition processes of droplets on leaves. This work provides a favorable reference for the study of the dynamic balance between wetting and adhesion properties of pesticide spray on leaf surfaces.

Concave/Convex Curvature of Anisotropic Grooves Differentially Alters Cellular Morphology, Adhesion, and Proliferation.

Curvature is an integral part of the complex in vivo tissue architecture across various length scales. Therefore, several in vitro models with a patterned curvature in different length scales have been developed to understand the role of this in cellular behavior. At the subcellular scale, wavy patterns have been reported wherein concave and convex grooves are adjacently present. However, the independent effect of continuous subcellular concave and convex shapes has not been reported, mainly owing to the limitations in fabricating such patterns. In this study, we developed continuous concave and convex grooves on polydimethylsiloxane (PDMS) using a Dracaena sanderiana (bamboo) leaf as a template. The first (negative) replica from the abaxial side of the bamboo leaf, which imparted concave grooves on PDMS, was subsequently used as a template to fabricate a positive replica of the leaf, resulting in convex grooves of the same size and arrangement as the concave grooves. We examined the influence of the groove curvature on the morphology of bone marrow-derived human mesenchymal stem cells (BM-hMSCs) and skeletal muscle cells (C2C12). BM-hMSCs and C2C12 cells aligned on both concave and convex grooves as compared to the random orientation on a flat substrate. The significant difference was observed in the morphology of both cells, in terms of area, aspect ratio, number, and length of protrusions on concave and convex patterns. We found that the number of protrusions was also dependent on the ratio of cell to pattern length scale for convex-shaped grooves but independent of length scale for concave-shaped grooves. The proliferation of BM-hMSCs was also found to be different on concave and convex shapes. Therefore, this study shows the importance of (1) convex and concave curvatures of the subcellular length scale in cellular response, (2) dependence on the ratio of cell and curvature length scale, and (3) use of natural templates for overcoming fabrication challenges.

Effect of light-induced changes in leaf anatomy on intercellular and cellular components of mesophyll resistance for CO2 in Fagus sylvatica.

Mesophyll resistance for CO2 diffusion (rm) is one of the main limitations for photosynthesis and plant growth. Breeding new varieties with lower rm requires knowledge of its distinct components. We tested new method for estimating the relative drawdowns of CO2 concentration (c) across hypostomatous leaves of Fagus sylvatica. This technique yields values of the ratio of the internal CO2 concentrations at the adaxial and abaxial leaf side, cd/cb, the drawdown in the intercellular air space (IAS), and intracellular drawdown between IAS and chloroplast stroma, cc/cbd. The method is based on carbon isotope composition of leaf dry matter and epicuticular wax isolated from upper and lower leaf sides. We investigated leaves from tree-canopy profile to analyse the effects of light and leaf anatomy on the drawdowns and partitioning of rm into its inter- (rIAS) and intracellular (rliq) components. Validity of the new method was tested by independent measurements of rm using conventional isotopic and gas exchange techniques. 73% of investigated leaves had adaxial epicuticular wax enriched in 13C compared to abaxial wax (by 0.50‰ on average), yielding 0.98 and 0.70 for average of cd/cb and cc/cbd, respectively. The rIAS to rliq proportion were 5.5:94.5% in sun-exposed and 14.8:85.2% in shaded leaves. cc dropped to less than half of the atmospheric value in the sunlit and to about two-thirds of it in shaded leaves. This method shows that rIAS is minor but not negligible part of rm and reflects leaf anatomy traits, i.e. leaf mass per area and thickness.

Resistance and susceptibility of different Barbarea (Brassicaceae) species and types to cabbage whitefly (Hemiptera: Aleyrodidae) and cabbage white butterfly (Lepidoptera: Pieridae)

Several Barbarea spp. (Brassicaceae) have been tested as trap crops for the diamondback moth Plutella xylostella L. (Lepidoptera: Plutellidae). The use of trap crops can be affected by their susceptibility to other pests, especially if the purpose is to reduce insecticide use. Barbarea rupicola Moris, B. verna (Mill.) Asch., and B. vulgaris Aiton (types G and P) (Brassicaceae) were tested for their susceptibility to the cabbage whitefly Aleyrodes proletella L. (Hemiptera: Aleyrodidae). The percentage of plants showing infestation by cabbage whiteflies ranged from 50% in G-type B. vulgaris and 8.3% in B. verna to no infestation at all in B. rupicola and P-type B. vulgaris. On the other hand, 95.8% of P-type plants showed symptoms of powdery mildew, Erysiphe cruciferarum Opiz ex L. Junell (Erysiphales: Erysiphaceae), while the G type and the other Barbarea spp. were unaffected by this pathogen. Additionally, the G and P types were used in two-choice oviposition preference tests to compare their attractiveness to the small white butterfly Pieris rapae L. (Lepidoptera: Pieridae). No significant differences in total oviposition per plant were found between the two types, but within-plant differences show that the small white butterfly prefers to oviposit on the adaxial leaf side in the P type. This study indicates that in locations where the cabbage whitefly is an economic pest, B. verna, which can also be used as a dead-end trap crop for the diamondback moth, could be chosen over G-type B. vulgaris.

Amphistomy: stomata patterning inferred from 13C content and leaf-side-specific deposition of epicuticular wax.

The benefits and costs of amphistomy (AS) vs. hypostomy (HS) are not fully understood. Here, we quantify benefits of access of CO2 through stomata on the upper (adaxial) leaf surface, using 13C abundance in the adaxial and abaxial epicuticular wax. Additionally, a relationship between the distribution of stomata and epicuticular wax on the opposite leaf sides is studied. We suggest that the 13C content of long-chain aliphatic compounds of cuticular wax records the leaf internal CO2 concentration in chloroplasts adjacent to the adaxial and abaxial epidermes. This unique property stems from: (1) wax synthesis being located exclusively in epidermal cells; and (2) ongoing wax renewal over the whole leaf lifespan. Compound-specific and bulk wax 13C abundance (δ) was related to amphistomy level (ASL; as a fraction of adaxial in all stomata) of four AS and five HS species grown under various levels of irradiance. The isotopic polarity of epicuticular wax, i.e. the difference in abaxial and adaxial δ (δab - δad), was used to calculate the leaf dorsiventral CO2 gradient. Leaf-side-specific epicuticular wax deposition (amphiwaxy level) was estimated and related to ASL. In HS species, the CO2 concentration in the adaxial epidermis was lower than in the abaxial one, independently of light conditions. In AS leaves grown in high-light and low-light conditions, the isotopic polarity and CO2 gradient varied in parallel with ASL. The AS leaves grown in high-light conditions increased ASL compared with low light, and δab - δad approached near-zero values. Changes in ASL occurred concomitantly with changes in amphiwaxy level. Leaf wax isotopic polarity is a newly identified leaf trait, distinguishing between hypo- and amphistomatous species and indicating that increased ASL in sun-exposed AS leaves reduces the CO2 gradient across the leaf mesophyll. Stomata and epicuticular wax deposition follow similar leaf-side patterning.

Volatile compositions and glandular trichomes of Zataria multiflora in different phenological stages under normal and drought stress conditions

BackgroundZataria multiflora Boiss. is a medicinal and aromatic plant from the Lamiaceae family. It is extensively used in Iranian traditional medicine, mostly as a replacement for Thyme species. This study was focused on the analysis of chemical composition and the distribution and types of trichomes of Z. multiflora grown under different conditions. Equilibrium headspace analysis in combination with GC-FID-MS was used to identify volatile compounds released by aerial parts of Z. multiflora in development stages of 50 and 100% flowering under normal and drought-stress conditions.ResultsThe main constituents were p-cymene (20.06–27.40%), γ-terpinene (12.44–16.93%), and α-pinene (6.91–16.58%) and thymol (8.52–9.99%). The highest content of p-cymene (27.40%) and thymol (9.99%) was observed in the 50% flowering stage at the 90% field capacity, while the maximum γ-terpinene (16.93%) content was recorded in the 100% flowering stage under normal conditions. Using the SEM method, it was found that peltate glandular and non-glandular trichomes are distributed on the surface of the leaf, stem, and outer side of the calyx. However, capitate trichomes only are detected on the stem and calyx in the 100% flowering and beginning of blooming stages, respectively. The type and structure of trichomes do not vary in different development stages, but they differ in density. The highest number of leaf peltate glandular trichomes was observed in the vegetative and beginning of blooming stages at 50% and 90% field capacity, respectively. Non-glandular trichomes of the stem were observed with high density in both normal and stress conditions, which are more densely in 90% field capacity.ConclusionsSince this plant has strong potential to be used in the food and pharmacological industries, this study provides valuable information for its cultivation and harvesting at specific phenological stages, depending on desired compounds and their concentrations.

Powdery mildew caused by Erysiphe corylacearum: An emerging problem on hazelnut in Italy.

Erysiphe corylacearum has recently been reported in northern Italy (Piedmont) and other European countries as the causal agent of a new emerging powdery mildew on hazelnut. This disease is much more dangerous than the common hazelnut powdery mildew caused by Phyllactinia guttata as it significantly reduces yield and quality of hazelnuts. This study aimed to perform morphological and molecular characterization of the fungal isolates from powdery mildew-infected plants in the Piedmont Italian region. Additionally, genetic diversity studies and pathogenicity tests were conducted. Thirty-six fungal isolates originating from symptomatic hazelnut plants exhibiting specific powdery mildew symptoms on the superior leaf side were identified morphologically as E. corylacearum. Single- and multilocus sequence typing of five loci (ITS, rpb2, CaM, GAPDH and GS) assigned all isolates as E. corylacearum. Multilocus and GAPDH phylogenetic studies resulted in the most efficient characterization of E. corylacearum. Studied fungal isolates were able to cause new emerging powdery mildew disease by fulfilling Koch's postulates. The emergence of powdery mildew disease in Italy revealed the E. corylacearum subgrouping, population expansion, and high nucleotide similarity with other recently identified E. corylacearum hazelnut isolates. To contain this harmful disease and inhibit the fungus spread into new geographical zones, it will be necessary to implement more rigorous monitoring in neighboring hazelnut plantations near infected hazelnuts, use sustainable fungicides and search for new biocontrol agents.

Micromorphological and Chemical Characterization of Drimys winteri Leaf Surfaces: The Secondary Alcohols Forming Epicuticular Wax Crystals Are Accompanied by Alkanediol, Alkanetriol and Ketol Derivatives.

The cuticle is a hydrophobic coating of most aerial plant surfaces crucial for limiting non-stomatal water loss. Plant cuticles consist of the lipid polyester cutin and associated waxes with compositions varying widely between plant species and organs. Here, we aimed to provide a comparative analysis of the dark-glossy adaxial and pale-glaucous abaxial sides of Drimys winteri (Winteraceae) leaves. Scanning electron microscopy showed nanotubular wax crystals lining the entire abaxial side of the leaf (including stomatal pores), while the adaxial side had patches of mixed platelet/tubule crystals and smooth areas between them. Consecutive treatments for wax removal and cutin depolymerization revealed that the waxes were deposited on a cutin network with micron-scale cavities across the entire abaxial surface including the stomata pores, and on a microscopically smooth cutin surface on the adaxial side of the leaf. Gas chromatography coupled to mass spectrometry and flame ionization detection showed that the wax mixtures on both sides of the leaf were complex mixtures of very-long-chain compounds dominated by the secondary alcohol nonacosan-10-ol and alkanediols with one hydroxyl on C-10. It is therefore very likely that the characteristic tubular wax crystals of both leaf sides are formed by these alcohols and diols. Further secondary alcohols and alkanediols, as well as ketols and alkanetriols with one functional group on C-10, were identified based on mass spectral fragmentation patterns. The similarities between all these mid-chain-functionalized compounds suggest that they are derived from nonacosan-10-ol via regio-specific hydroxylation reactions, likely catalyzed by three P450-dependent monooxygenases with different regio-specificities.

Spectral Library of Plant Species from Montesinho Natural Park in Portugal

In this work, we present and describe a spectral library (SL) with 15 vascular plant species from Montesinho Natural Park (MNP), a protected area in Northeast Portugal. We selected species from the vascular plants that are characteristic of the habitats in the MNP, based on their prevalence, and also included one invasive species: Alnus glutinosa (L.) Gaertn, Castanea sativa Mill., Cistus ladanifer L., Crataegus monogyna Jacq., Frangula alnus Mill., Fraxinus angustifolia Vahl, Quercus pyrenaica Willd., Quercus rotundifolia Lam., Trifolium repens L., Arbutus unedo L., Dactylis glomerata L., Genista falcata Brot., Cytisus multiflorus (L’Hér.) Sweet, Erica arborea L., and Acacia dealbata Link. We collected spectra (300–2500 nm) from five records per leaf and leaf side, which resulted in 538 spectra compiled in the SL. Additionally, we computed five vegetation indices from spectral data and analysed them to highlight specific characteristics and differences among the sampled species. We detail the data repository information and its organisation for a better understanding of the data and to facilitate its use. The SL structure can add valuable information about the selected plant species in MNP, contributing to conservation purposes. This plant species SL is publicly available in Zenodo platform.

The PROLIB leaf radiative transfer model: Simulation of the dorsiventrality of leaves from visible to mid-wave infrared

Many plant species have dorsiventral leaves that have significant differences in optical properties from one side to the other. Several studies have revealed that ignoring this asymmetry induces significant errors in plant canopy reflectance, and current leaf models simulating leaf dorsiventrality are limited to the 0.4–2.5 μm wavelength range. This article, partly based on two recently collected datasets in the 2.5–14 μm wavelength range, demonstrates that ignoring leaf dorsiventrality induces significant errors in brightness temperature and effective emissivity at the canopy scale. The PROLIB model, which inherits from the PROSPECT-VISIR and LIBERTY models, is the first radiative transfer model to simulate the reflectance and transmittance of both leaf sides from 0.4 to 5.7 μm. The palisade and spongy mesophylls are represented as plate and sphere layers, respectively, to account for the structural asymmetry of leaf cells. The sieve effect that explains the differences in transmittance between the adaxial and abaxial sides of the leaf is successfully incorporated into PROLIB. Evaluation of the model on several leaf datasets shows that: (1) It reproduces well the adaxial and abaxial optical properties of the leaves, with a root mean square error (RMSE) of 0.0109 for reflectance and transmittance. (2) It can be inversed to retrieve leaf traits, with RMSE values for leaf chlorophyll, carotenoid, anthocyanin, water, and dry matter content of 5.519 μg/cm2, 2.344 μg/cm2, 4.219 μg/cm2, 0.0022 g/cm2, and 0.0017 g/cm2, respectively (corresponding normalized RMSE values of 22.0%, 34.0%, 49.4%, 19.6%, and 24.7%). However, better and more complete leaf datasets are needed for leaf dorsiventrality analysis and model calibration.

First Report of Powdery Mildew on Viburnum chinshanense Caused by Erysiphe pseudoviburni in China.

Viburnum chinshanense, a deciduous shrub in the family Caprifoliaceae, is a dominant tree distributed mainly in the North-Central and South-Central regions of China (Zhu et al. 2023). Because of its lush white flowers and vibrant red fruits, V. chinshanense is used widely as ornamental tree in China. In May 2022, severe powdery mildew symptoms were observed on V. chinshanense on the Huaxi Campus of Guizhou Normal University, Guiyang, China. The incidence was approximately 75% among 80 V. chinshanense plants observed. White mycelia were present on both adaxial and abaxial leaf sides, but not on fruits, petioles, or stems. Infected leaves showed slight chlorosis and twisting. The mycelia were amphigenous, forming small-to-large patches, often sparse on the upper leaf surface, but mostly confluent on the lower leaf surface. Hyphae were hyaline, 4-7 μm wide. Hyphal appressoria were lobed to multilobed, in opposite pairs or solitary. Conidiophores were erect, straight, or somewhat flexuous, 60-130 µm long (n = 30). Foot cells were subcylindrical to slightly curved-sinuous at the base, 20-40 × 6-10 µm (n = 30) in size, followed by 1-3 shorter cells. Conidia formed singly, occasionally two to three in a chain. Conidia were ellipsoid to ovoid, cylindrical, and 24-40 × 16-20 µm (n = 50). No fibrosin bodies were observed on the conidia. Chasmothecia were subglobose, 56-115 µm in diameter. The appendages were 35-70 µm long. Based on these morphological characteristics, the powdery mildew fungus was identified as Erysiphe pseudoviburni (Bradshaw et al. 2020). To confirm the identification, the ribosomal DNA internal transcribed spacer (ITS) and the ribosomal large subunit (LSU) region were amplified and sequenced using the ITS1/ITS4 primer pair (White et al. 1990) and the NL1/NL4 primer pair (Ziemiecki et al. 1990), respectively. The obtained 643-bp ITS sequence (GenBank accession no. ON729292) had 99.84% identity with E. pseudoviburni strains KUS-F27310 (MN431595) and MUMH0001 (LC009904). The obtained 593-bp LSU sequence (ON729293) had 99.83% identity with E. pseudoviburni (LC009904 and MN431595). Based on the phylogenetic analysis of the combined ITS and LSU dataset (Bradshaw et al. 2020), the isolate (GZVD-1) was grouped in a clade with the E. pseudoviburni strains KUS-F27319, KUS-F27310, and MUMH0001. To fulfill Koch's postulates, leaves of three healthy potted V. chinshanense plants were inoculated by gently pressing with diseased leaves. Non-contact plants were used as controls. All plants were incubated in a greenhouse at 25 ± 2°C, 80% relative humidity. Similar powdery mildew symptoms were observed on the inoculated plants 12 days after inoculation, whereas the control plants remained symptomless. The reisolated fungus from the inoculated plants was morphologically identical to that on originally diseased plants. ITS and LSU sequences of the reisolated fungus showed 100% identity with ON729292 and ON729293, respectively. E. pseudoviburni has previously been reported to infect some Viburnum species, including V. sieboldii in Japan (Takamatsu et al. 2015) and V. odoratissimum in South Korea (Bradshaw et al. 2020). To the best of our knowledge, this is the first report of powdery mildew caused by E. pseudoviburni on V. chinshanense in China. This work expands the known host range of E. pseudoviburni in the Viburnum genus.

Chemical and structural heterogeneity of olive leaves and their trichomes

Many biological surfaces have hairs, known as trichomes in plants. Here, the wettability and macro- and micro-scale features of olive leaves are analyzed. The upper leaf side has few trichomes, while the lower side has a high trichome density. By combining different techniques including electron and atomic force microscopy, trichome surfaces are found to be chemically (hydrophilic-hydrophobic) heterogeneous at the nano-scale. Both olive leaf surfaces are wettable by water, having a high water contact angle hysteresis and great drop adhesion. The ultra-structural pattern observed for epidermal pavement cells differs from the reticulate cuticle structure of trichomes which shows that leaf surface areas may be substantially different despite being located nearby. Our study provides evidence for the nano-scale chemical heterogeneity of a trichome which may influence the functional properties of biological surfaces, such as water and solute permeability or water capture as discussed here for plants.

Morphology and excreting-function of microhairs in salt-tolerant Zoysia japonica, comparing adaxial and abaxial leaf surfaces

Bicellular trichomes called ‘microhairs’ are known as ‘salt glands’ in some Chloridoideae in the Poaceae. The adaxial leaf surface of Zoysia japonica, a salt-tolerant grass, excretes salts, whereas the abaxial leaf surface does not. In this study, we investigated the morphology and excreting-function of the microhairs of Z. japonica, comparing the adaxial and abaxial leaf surfaces. Scanning electron microscopy of the leaf surfaces showed the distribution of microhairs on both sides and revealed significant excretion on the adaxial side but a small excretion on the abaxial side. Energy-dispersive X-ray spectrometry revealed that microhairs on the adaxial side excrete sodium, magnesium, and chlorine, whereas those on the abaxial side excrete or secrete insoluble substances, which sometimes contain silicon. Transmission electron microscopy was used to clarify the ultrastructure of microhairs, as in the first detailed report on Zoysia spp.; however, the microhairs on both leaf sides showed typical structures of bicellular salt glands reported in Chloridoideae. The cap cells of the microhairs had smooth surfaces without epicuticular wax structures. These results indicate that the ultrastructural features of Z. japonica microhairs are important for understanding physiological mechanisms in common with salt-excretion and the excretion or secretion of other substances.

Cultivar was more influential than bacterial strain and other experimental factors in recovery of Escherichia coli O157:H7 populations from inoculated live Romaine lettuce plants.

The varied choice of bacterial strain, plant cultivar, and method used to inoculate, retrieve, and enumerate Escherichia coli O157:H7 from live plants could affect comparability among studies evaluating lettuce-enterobacterial interactions. Cultivar, bacterial strain, incubation time, leaf side inoculated, and sample processing method were assessed for their influence in recovering and quantifying E. coli O157:H7 from live Romaine lettuce. Cultivar exerted the strongest effect on E. coli O157:H7 counts, which held up even when cultivar was considered in interactions with other factors. Recovery from the popularly grown green Romaine "Rio Bravo" was higher than from the red variety "Outredgeous." Other modulating variables were incubation time, strain, and leaf side inoculated. Sample processing method was not significant. Incubation for 24 hours post-lettuce inoculation yielded greater counts than 48 hours, but was affected by lettuce cultivar, bacterial strain, and leaf side inoculated. Higher counts obtained for strain EDL933 compared to a lettuce outbreak strain 2705C emphasized the importance of selecting relevant strains for the system being studied. Inoculating the abaxial side of leaves gave higher counts than adaxial surface inoculation, although this factor interacted with strain and incubation period. Our findings highlight the importance of studying interactions between appropriate bacterial strains and plant cultivars for more relevant research results, and of standardizing inoculation and incubation procedures. The strong effect of cultivar exerted on the E. coli O157:H7-lettuce association supports the need to start reporting cultivar information for illness outbreaks to facilitate the identification and study of plant traits that impact food safety risk.IMPORTANCEThe contamination of Romaine lettuce with Escherichia coli O157:H7 has been linked to multiple foodborne disease outbreaks, but variability in the methods used to evaluate E. coli O157:H7 association with live lettuce plants complicates the comparability of different studies. In this study, various experimental variables and sample processing methods for recovering and quantifying E. coli O157:H7 from live Romaine lettuce were assessed. Cultivar was found to exert the strongest influence on E. coli O157:H7 retrieval from lettuce. Other modulating factors were bacterial incubation time on plants, strain, and leaf side inoculated, while sample processing method had no impact. Our findings highlight the importance of selecting relevant cultivars and strains, and of standardizing inoculation and incubation procedures, in these types of assessments. Moreover, results support the need to start reporting cultivars implicated in foodborne illness outbreaks to facilitate the identification and study of plant traits that impact food safety risk.

Application of ZnO Nanoparticles Encapsulated in Mesoporous Silica on the Abaxial Side of a Solanum lycopersicum Leaf Enhances Zn Uptake and Translocation via the Phloem.

Foliar application of nutrient nanoparticles (NPs) is a promising strategy for improving fertilization efficiency in agriculture. Phloem translocation of NPs from leaves is required for efficient fertilization but is currently considered to be feasible only for NPs smaller than a cell wall pore size exclusion limit of <20 nm. Using mass spectrometry imaging, we provide here the first direct evidence for phloem localization and translocation of a larger (∼70 nm) fertilizer NP comprised of ZnO encapsulated in mesoporous SiO2 (ZnO@MSN) following foliar deposition. The Si content in the phloem tissue of the petiole connected to the dosed leaf was ∼10 times higher than in the xylem tissue, and ∼100 times higher than the phloem tissue of an untreated tomato plant petiole. Direct evidence of NPs in individual phloem cells has only previously been shown for smaller NPs introduced invasively in the plant. Furthermore, we show that uptake and translocation of the NPs can be enhanced by their application on the abaxial (lower) side of the leaf. Applying ZnO@MSN to the abaxial side of a single leaf resulted in a 56% higher uptake of Zn as well as higher translocation to the younger (upper) leaves and to the roots, than dosing the adaxial (top) side of a leaf. The higher abaxial uptake of NPs is in alignment with the higher stomatal density and lower density of mesophyll tissues on that side and has not been demonstrated before.

Airborne hyperspectral imaging for early diagnosis of kimchi cabbage downy mildew using 3D-ResNet and leaf segmentation

Kimchi cabbage (Brassica rapa pekinensis), one of the main agricultural products in Korea, is susceptible to downy mildew disease infections. Infected plants develop yellow spots (chlorosis) on the upper (adaxial) side of the infected leaf, undermining cabbage production and quality. An early detection method to recognize and treat the disease is crucial to prevent downy mildew and lessen its physical effects on plants. Hyperspectral imaging can capture data from a broad spectrum, which can be utilized to detect disease occurrence before any visible symptoms appear. Combining a hyperspectral camera with an unmanned aerial vehicle (UAV) can provide a non-destructive, field-scale disease detection system. In this study, three-dimensional (3D) convolutional neural network (CNN) models were used to simultaneously account for the spectral and spatial features of the disease to enable automatic disease detection. Using a 3D-residual network (ResNet) CNN with four residual blocks, each followed by a rectified linear unit activation function and a max-pooling layer, helped achieve an overall accuracy of 0.876 and a diseased class accuracy of 0.873. Disease severity was estimated by grouping nearby diseased leaves using the density-based spatial clustering of applications with noise clustering algorithm to achieve a 27.07 % relative error or a 1.08 level difference from the actual.

Trichomes affect grapevine leaf optical properties and thermoregulation

In the context of climate change, the optical properties of grapevine leaves have been used in imaging technologies to screen grapevine phenotypes tolerant to water deficit and heat waves in field conditions. Image-based plant phenotyping is challenging because the adaxial and the abaxial sides of the leaf present different morphology. This study investigated the effect of trichomes of the abaxial epidermis on the spectral responses in the two grapevine leaf sides. It was also examined the effect of pubescence on leaf thermoregulation, either during water deficiency or not. For this study, 99 Vitis spp. genotypes were categorised for their prostrate trichome density between main veins on the abaxial side of the leaves (using the descriptor OIV 084). In the first week of 2022, August, reflectance spectra from 400 to 700 nm and color indexes CIELAB and RGB were recorded in five leaves (both abaxial and adaxial sides) per genotype. During three days in midsummer, crop water stress index (CWSI) was also determined in each genotype. The abaxial leaf side was more reflective than the adaxial one in all visible color bands. Values of CIELAB (except for component a*) and RGB were higher for the abaxial leaf side than the adaxial one. The different spectral and color responses between leaf sides positively correlated with the descriptor OIV 084. Trichomes, which mainly occur on the abaxial side in grapevine, significantly contribute to the different optical properties between the two leaf sides. Correlation between OIV 084 and CWSI values was significantly positive (p < 0.05) only when vines were under drought, indicating that trichomes rise leaf temperature by probably reducing evaporative cooling under dry conditions. Therefore, pubescence could be a promising trait to consider when selecting varieties for drought tolerance.

Photosynthetic performance under adaxial and abaxial illumination in three Mediterranean Quercus species differing in branch architecture and individual leaf area.

Light availability effects on canopy-level carbon balance constitute an especially difficult issue to address, owing to the strong spatial and temporal changes of the light environment within the canopy. One of the least explored aspects in relation to light environment is the interaction between leaf angle and leaf anatomy. The inclination of the leaf may affect the distribution of light between the adaxial and abaxial surface. The purpose of this study is determining the proportions of the leaf area receiving light from the abaxial side in branches of isolated trees in three Mediterranean oaks, as well as the photosynthetic responses to light under adaxial and abaxial illumination. The proportions of the leaf area illuminated from below were low for sun incidence angles near 0° with respect to the main axis of the branch. However, for sun incidence angles about 45°, the proportion of leaves receiving abaxial illumination was considerable. PPFD levels on the sunlit part of the abaxial surface were always lower than those in the upper leaf side, as a consequence of the lower projection efficiency for the leaves facing the sun by the lower side. Light absorptance was also lower on the abaxial side. The differences between both sides of the leaf tended to be stronger for thicker, longer-living leaves. We conclude that mean C assimilation of the canopy is significantly decreased by the presence of leaves facing the sun by the lower side and that this decrease is stronger in evergreen species with thicker leaves.

Triose phosphate utilization in leaves is modulated by whole-plant sink-source ratios and nitrogen budgets in rice.

Triose phosphate utilization (TPU) is a biochemical process indicating carbon sink-source (im)balance within leaves. When TPU limits leaf photosynthesis, photorespiration-associated amino acid exports probably provide an additional carbon outlet and increase leaf CO2 uptake. However, whether TPU is modulated by whole-plant sink-source relations and nitrogen (N) budgets remains unclear. We address this question by model analyses of gas-exchange data measured on leaves at three growth stages of rice plants grown at two N levels. Sink-source ratio was manipulated by panicle pruning, by using yellower-leaf variant genotypes, and by measuring photosynthesis on adaxial and abaxial leaf sides. Across all these treatments, higher leaf N content resulted in the occurrence of TPU limitation at lower intercellular CO2 concentrations. Photorespiration-associated amino acid export was greater in high-N leaves, but was smaller in yellower-leaf genotypes, panicle-pruned plants, and for abaxial measurement. The feedback inhibition of panicle pruning on rates of TPU was not always observed, presumably because panicle pruning blocked N remobilization from leaves to grains and the increased leaf N content masked feedback inhibition. The leaf-level TPU limitation was thus modulated by whole-plant sink-source relations and N budgets during rice grain filling, suggesting a close link between within-leaf and whole-plant sink limitations.