Search Results (17)

Fire blight is a highly destructive plant disease that affects the pome fruit value chain, with high economic impacts. Its etiological agent is the Gram-negative bacterium Erwinia amylovora. The origin of fire blight goes back to the late 1700s in North America, and the disease since then has spread to New Zealand, Europe, North Africa, the Middle East, and Asia. Due to its worldwide dissemination, advances have been made to identify and characterize E. amylovora strains from different regions and understand their evolutionary adaptation. Additionally, many efforts have been made in recent decades to stop the occurrence and impacts of fire blight, but in many countries, only preventive measures have been applied, as the application of antibiotics and copper-based compounds has become more restricted. Thus, new sustainable methods to control the pathogen are constantly required. This article presents a comprehensive review of the pathogen, from the phenotypic and molecular characterization methods applied to advances in comparative genomics and the development of new compounds for sustainable control of E. amylovora. Full article

The bacterium Erwinia amylovora causes fire blight and continues to threaten global commercial apple and pear production. Conventional microbiology techniques cannot accurately determine the presence of live pathogen cells in fire blight cankers. Several factors may prevent E. amylovora from growing on solid culture media, including competing microbiota and the release of bacterial-growth-inhibitory compounds by plant material during sample processing. We previously developed a canker processing methodology and a chip-based viability digital PCR (v-dPCR) assay using propidium monoazide (PMA) to bypass these obstacles. However, sample analysis was still time-consuming and physically demanding. In this work, we improved the previous protocol using an automatic tissue homogenizer and transferred the chip-based v-dPCR to the BioRad QX200 droplet dPCR (ddPCR) platform. The improved sample processing method allowed the simultaneous, fast, and effortless processing of up to six samples. Moreover, the transferred v-ddPCR protocol was compatible with the same PMA treatment and showed a similar dynamic range, from 7.2 × 10² to 7.6 × 10⁷ cells mL⁻¹, as the previous v-dPCR. Finally, the improved protocol allowed, for the first time, the detection of E. amylovora viable but nonculturable (VBNC) cells in cankers and bark tissues surrounding cankers. Our v-ddPCR assay will enable new ways to evaluate resistant pome fruit tree germplasm, further dissect the E. amylovora life cycle, and elucidate E. amylovora physiology, epidemiology, and new options for canker management. Full article

Wood-boring insect pests pose a significant threat to orchards, potentially leading to tree mortality. In the initial stages of infestation, no visible symptoms are apparent, but as infestations progress, rapid and widespread symptoms emerge, resulting in accelerated tree decline. Therefore, the timely detection of early wood-boring insect symptoms is critical for effective pest control, necessitating advanced methods such as remote sensing. In this study, remote sensing is utilized to identify the early symptoms of peach flatheaded root borer (PFRB) infestation in trees. A multispectral sensor attached to a UAV captures aerial imagery data from stone fruit and pome fruit orchards. These data undergo processing in photogrammetric and GIS programs, where NDVI, NDRE, and the tree crown area are computed. On-site observations confirm PFRB infestations. Various machine-learning models, including logistic regression (LR), artificial neural network (NN), random forest (RF), and extreme gradient boosting (XGBoost), are compared using mean NDVI values, mean NDRE values, crown area, mean temperature, and mean relative humidity. Mean NDVI values emerge as the most crucial factor for predicting PFRB infestation across all machine-learning models. The XGBoost model proves the most effective, achieving an accuracy of 0.85, with marginal variations from the other tested models. Full article

Apple chlorotic leaf spot virus (ACLSV) (genus, Trichovirus; family, Betaflexiviridae) is a widespread, deleterious, and the most damaging pathogen of pome and fruit trees including domesticated apple (Malus × domestica Borkh.), to which it is transmitted by grafting and pruning. The positive-sense, single-stranded RNA virus is 600–700 nm long and has a genome of 74.7–7.56 kbp in size, minus the poly-A tail and 3′- and 5′-untranslated regions. The genome has three overlapping open reading frames (ORFs) that encode a replication-associated protein (Rep), movement protein (MP), and coat protein (CP). RNA interference (RNAi)-mediated antiviral defense in eukaryotes has evolved to control infections in plant viruses. The objective of this study was to analyze locus-derived microRNAs (mdm-miRNAs) in the apple genome with potential for targeting ACLSV +ssRNA-encoded mRNAs, using a predictive approach that involves four algorithms. The goal is to mobilize the in silico-predicted endogenous mdm-miRNAs and trigger the RNAi pathway experimentally in apple trees to evaluate antiviral resistance to ACLSV. Experimentally validated apple (2n = 2X = 34) mdm-miRNAs (n = 322) were obtained from the miRBase database and aligned to the ACLSV genome (KU870525). Of the 322 targeting mature locus-derived mdm-miRNAs analyzed, nine apple mdm-miRNA homologs (mdm-miR395k, mdm-miR5225c, and mdm-miR7121 (a, b, c, d, e, f, g, h) were predicted by all “four algorithms”, whereas fifty-eight mdm-miRNAs were identified as consensus binding sites by the combined results of two algorithms. The miRanda, RNA22, and TAPIR algorithms predicted binding of mdm-miR395k at nucleotide position 4691 and identified it as the most effective interacting mdm-miRNA targeting the virus ORF1 sequence. An integrated Circos plot was generated to validate the accuracy of target prediction and determine if apple mdm-miRNAs could bind to the predicted ACLSV mRNA target(s). A genome-wide in silico-predicted miRNA-mediated target gene regulatory network was implicated to validate interactions necessary to warrant in vivo analysis. The availability of validated locus-derived microRNAs (mdm-miRNAs) with predicted potential to target ACLSV in infected apple trees represents the first step toward development of ACLSV-resistant apple trees. Full article

Most nashi cultivars require heavy thinning, and this has traditionally been performed by the time and labour-intensive practice of hand thinning. Crop load management is a key cost driver for nashi production, but there are limited cost-effective options available for nashi growers compared to other pome fruit, especially apples and, to a lesser extent, European pears. There is, however, potential to adapt some of the thinning tools and techniques used in apples and European pears to reduce the labour requirements and high cost of thinning in nashi, thus improving industry profitability. Several chemical thinning agents have potential for nashi, and an understanding of the optimal application rates, times and weather conditions for each chemical, as well as the conditions/factors that impact the tree carbon balance, will improve the predictability of chemical thinning. However, it is difficult to target specific flowers/fruitlets within a cluster with chemicals, and the flowers that produce the preferred fruit shape and size are in the middle of the flower cluster. Mechanical thinning during the flowering period with either Darwin or BAUM-style string thinners has potential, particularly as these devices can be used as early as flower emergence. As for chemical thinning, the issue of non-selectivity needs to be addressed; however, the development of mechatronic systems should overcome most problems that occur with the currently available mechanical thinners. Shading at critical times is an avenue that could be explored further to ascertain the critical stage when developing fruit are susceptible to enable the determination of the optimal timing and duration of shading. Targeted pruning and bud thinning during the dormant winter period to reduce the floral bud numbers is a valuable option for the precise placement of fruit in optimal positions and to set up the required number of clusters. This review highlighted several tools/techniques that, with further work, can be incorporated into a systematic approach to crop load management in nashi while reducing the risk and cost. Full article

In the European Union (EU), a total of 11,301,345 hectares are dedicated to the cultivation of fruit trees, mainly olive orchards, grapevines, nut trees (almond, walnut, chestnut, hazelnut, and pistachio), apple and pear trees, stone fruit trees (peach, nectarine, apricot, cherry, and plum), and citrus fruit trees (orange, clementine, satsuma, mandarin, lemon, grapefruit, and pomelo). Pruning these trees, together with plantation removal to a lesser extent, produces a huge amount of wood waste. A theoretical calculation of the wood waste in the European Union estimates approximately 2 and 25 million tons from wood plantation removal and pruning, respectively, per year. This wood waste is usually destroyed by in-field burning or crushing into the soil, which result in no direct economic benefits. However, wood from tree pruning, which is enriched in high added-value molecules, offers a wide spectrum of possibilities for its valorization. This review focuses on the contribution of wood waste to both sustainability and the circular economy, considering its use not only as biomass but also as a potential source of bioactive compounds. The main bioactive compounds found in wood are polyphenols, terpenes, polysaccharides, organic compounds, fatty acids, and alkaloids. Polyphenols are the most ubiquitous compounds in wood. Large amounts of hydroxytyrosol (up to 25 g/kg dw), resveratrol (up to 66 g/kg dw), protocatechuic acid (up to 16.4 g/kg), and proanthocyanins (8.5 g/kg dw) have been found in the wood from olive trees, grapevines, almond trees and plum trees, respectively. The bioactivity of these compounds has been demonstrated at lower concentrations, mainly in vitro studies. Bioactive compounds present antioxidant, antimicrobial, antifungal, biostimulant, anti-inflammatory, cardioprotective, and anticarcinogenic properties, among others. Therefore, wood extracts might have several applications in agriculture, medicine, and the food, pharmaceutical, nutraceutical, and cosmetics industries. For example, olive tree wood extract reduced thrombin-induced platelet aggregation in vitro; grapevine tree wood extract acts a preservative in wine, replacing SO₂; chestnut tree wood extract has antifungal properties on postharvest pathogens in vitro; and stone tree wood extracts are used for aging both wines and brandies. Moreover, the use of wood waste contributes to the move towards both a more sustainable development and a circular economy. Full article

Phenological records of apple and pear trees, including flowering, harvest and leaf drop, and concomitant weather records at Klein-Altendorf (50° N) near Bonn, Germany were correlated using two approaches: (a) linear curve fitting and (b) comparison of mean values of the first 30 years (1956–1988) versus the recent 30 years of climate change (1989–2017). The annual air temperature increased by 1.7 °C from 8.6 °C in 1958 to 10.3 °C in 2017 over the last 60 years and similarly in the vegetation period (1 April–30 October) from 13.7 °C in 1958 to 15.2 °C in 2017 by 1.5 °C. The combination of stronger increase in winter temperatures (by +1.2 °C) than in the summer (air +1.0 °C) with advanced bud break and −0.3 °C lower minimum temperatures in April during flowering resulted a continued risk of a late frost, as experienced in 2017. The strongest climate change effect, i.e., 11–14 days advanced flowering (in apple and pear) highly correlated (R² −0.7) with the March/April temperature. Fruit ontogeny was 4 days shorter in cv. ‘Lucas’ pear, but 5 days longer in cv. ‘Cox’ and 10 days longer in cv. ‘Boskoop’, but remained unchanged in cv. ‘Golden Delicious’, irrespective of early or late ripening variety and contradictory climate effects, fruit matured 4–12 days earlier indicating its sole dependency on variety. Climate data and (earlier) harvest date closely correlated (R²: 0.6–0.7). The lowest correlation was between canopy duration (bloom to leaf fall), which was consistently extended by 6–10 days and the leaf drop stage beginning 2–4 days earlier. The correlations indicated that the Meckenheim fruit growing region is strongly affected by climate change and the comparison between two equally-balanced 30-year phases gave more realistic results than linear curve fitting. Full article

Fire blight is a major pome fruit trees disease that is caused by the quarantine phytopathogenic Erwinia amylovora, leading to major losses, namely, in pear and apple productions. Nevertheless, no effective sustainable control treatments and measures have yet been disclosed. In that regard, antimicrobial peptides (AMPs) have been proposed as an alternative biomolecule against pathogens but some of those AMPs have yet to be tested against E. amylovora. In this study, the potential of five AMPs (RW-BP100, CA-M, 3.1, D4E1, and Dhvar-5) together with BP100, were assessed to control E. amylovora. Antibiograms, minimal inhibitory, and bactericidal concentrations (minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC), growth and IC₅₀ were determined and membrane permeabilization capacity was evaluated by flow cytometry analysis and colony-forming units (CFUs) plate counting. For the tested AMPs, the higher inhibitory and bactericidal capacity was observed for RW-BP100 and CA-M (5 and 5–8 µM, respectively for both MIC and MBC), whilst for IC₅₀ RW-BP100 presented higher efficiency (2.8 to 3.5 µM). Growth curves for the first concentrations bellow MIC showed that these AMPs delayed E. amylovora growth. Flow cytometry disclosed faster membrane permeabilization for CA-M. These results highlight the potential of RW-BP100 and CA-M AMPs as sustainable control measures against E. amylovora. Full article

The study’s objective was to evaluate the influence of thinning on the quality and regularity of yield of ‘Regina’ cherries grown on a dwarf Gisela 5 rootstock. The experiments were conducted in the years 2009–2012 in Western Poland. Trees were thinned using a chemical agent, ammonium thiosulphate (ATS), at doses of 20 g ATS L⁻¹, 30 g ATS L⁻¹ and 40 g ATS L⁻¹, and by hand, and the results of chemical and hand thinning were compared with those obtained for unthinned trees. The course of weather conditions in winter and during flowering had a significant impact on yield. Chemical thinning is known to be an effective method to regulate fruiting of pome trees, but it can also be successful if applied to cherry trees, as reflected by the alternate bearing index, which was the lowest after applying ATS at a dose of 40 g. ATS treatment improved fruit quality in full crop years. Thinning resulted in, among other things, larger and darker fruit and higher content of total soluble solids and titratable acidity. Treatment with 40 g ATS L⁻¹ significantly stimulated the vegetative growth of trees. Full article

Controlling fire blight in pear production areas depends strongly on regular visual inspections of pome fruit orchards, nurseries and other hosts of Erwinia amylovora. In addition, these inspections play an essential role in delineating fire blight free production areas, which has important implications for fruit export. However, visual monitoring is labor intensive and time consuming. As a potential alternative, the performance of spectral sensors on unmanned airborne vehicles (UAV) or drones was evaluated, since this allows the monitoring of larger areas compared to the current field inspections. Unlike more traditional remote sensing platforms such as manned aircrafts and satellites, UAVs offer a higher flexibility and an extremely high level of detail. In this project, a UAV platform carrying a hyperspectral COSI-cam camera was used to map a heavily infected pear orchard. The hyperspectral data were used to assess which wavebands contain information on fire blight infections. In this study, wavelengths 611 nm and 784 nm were found appropriate to detect symptoms associated with fire blight. Vegetation indices that allow to discriminate between healthy and infected trees were identified, too. This manuscript highlights the potential use of the UAV methodology in fire blight detection and remaining difficulties that still need to be overcome for the technique to become fully operational in practice. Full article

One hundred Prunus trees, including almond (P. dulcis), apricot (P. armeniaca), nectarine (P. persica var. nucipersica), peach (P. persica), plum (P. domestica), purple leaf plum (P. cerasifera) and sweet cherry (P. avium), were selected from growing regions Australia-wide and tested for the presence of 34 viruses and three viroids using species-specific reverse transcription-polymerase chain reaction (RT-PCR) or polymerase chain reaction (PCR) tests. In addition, the samples were tested using some virus family or genus-based RT-PCR tests. The following viruses were detected: Apple chlorotic leaf spot virus (ACLSV) (13/100), Apple mosaic virus (ApMV) (1/100), Cherry green ring mottle virus (CGRMV) (4/100), Cherry necrotic rusty mottle virus (CNRMV) (2/100), Cherry virus A (CVA) (14/100), Little cherry virus 2 (LChV2) (3/100), Plum bark necrosis stem pitting associated virus (PBNSPaV) (4/100), Prune dwarf virus (PDV) (3/100), Prunus necrotic ringspot virus (PNRSV) (52/100), Hop stunt viroid (HSVd) (9/100) and Peach latent mosaic viroid (PLMVd) (6/100). The results showed that PNRSV is widespread in Prunus trees in Australia. Metagenomic high-throughput sequencing (HTS) and bioinformatics analysis were used to characterise the genomes of some viruses that were detected by RT-PCR tests and Apricot latent virus (ApLV), Apricot vein clearing associated virus (AVCaV), Asian Prunus Virus 2 (APV2) and Nectarine stem pitting-associated virus (NSPaV) were also detected. This is the first report of ApLV, APV2, CGRMV, CNRNV, LChV1, LChV2, NSPaV and PBNSPaV occurring in Australia. It is also the first report of ASGV infecting Prunus species in Australia, although it is known to infect other plant species including pome fruit and citrus. Full article

After the first record in 2008 in Southeast Italy, the alien invasive and quarantine pest Aleurocanthus spiniferus (orange spiny whitefly—OSW) has gradually spread throughout Europe, infesting several new host plants in addition to the known hosts. Molecular characterization of some Italian populations and a newly found Albanian population highlighted two different haplotypes invading Europe, belonging to one of the haplogroups previously recorded in China. A predator was recorded for the first time in several fields in Italy in association with OSW and other whitefly species. It was successively identified through a morpho-molecular characterization as a Nearctic member of the tribe Serangiini, the ladybird beetle, Delphastus catalinae. This predator represents a promising biocontrol agent to manage A. spiniferus outbreaks in Italy and other invaded countries. Full article

Fire blight, which is caused by the bacteria Erwinia amylovora, remains one of the most important diseases limiting the productivity of apple and pear orchards in the United States. In commercial orchards, in-season fire blight management relies exclusively on the use of antibiotic treatments (such as streptomycin and oxytetracycline) and on bacterial biocontrol agents whose efficacy is limited. We hypothesize that the efficacy of the biocontrol agents can be greatly enhanced through targeted delivery to flowers, which serve as initial infection courts, using the Japanese orchard bee, Osmia cornifrons. Many factors, such as the synchrony of life cycle with plant phenology and specificity to pomaceous plants, suggest that O. cornifrons could be an excellent vector of the biocontrol products during bloom in pome tree fruits. However, deployment of this pollinator species to deliver biocontrol agents for fire blight control has not been attempted previously due to the lack of an efficient system to pack the bodies of the bees exiting nesting tubes with the biocontrol products. In this study, we design and test a dispenser system to facilitate the use of O. conifrons as a vector for commercially available biocontrol products for fire blight control. The effectiveness of O. conifrons to deliver biocontrol agents to flowers, and to effect secondary dissemination from treated to untreated flowers is also evaluated in greenhouse experiments. We found that the O. conifrons bees were able to use the nest dispenser designed for the delivery of biological control products, and are effective in vectoring and delivering the Bacillus subtilis-based biological control product (Serenade^®) to apple blossoms. We also found that the O. cornifrons were effective in secondary inoculation of this biological control product to newly-opened flowers. These findings suggest the potential use of commercially available O. conifrons and other orchard bees in targeted delivery of biological control products for fire blight, and possibly other diseases, in different fruit crops. Full article

Early and precise spatio-temporal monitoring of tree vitality is key for steering management decisions in pome fruit orchards. Spaceborne remote sensing instruments face a tradeoff between spatial and spectral resolution, while manned aircraft sensor-platform systems are very expensive. In order to address the shortcomings of these platforms, this study investigates the potential of Remotely Piloted Aircraft Systems (RPAS) to facilitate rapid, low cost, and flexible chlorophyll monitoring. Due to the complexity of orchard scenery a robust chlorophyll retrieval model on RPAS level has not yet been developed. In this study, specific focus therefore lies on evaluating the sensitivity of retrieval models to confounding factors. For this study, multispectral and hyperspectral imagery was collected over pome fruit orchards. Sensitivities of both univariate and multivariate retrieval models were demonstrated under different species, phenology, shade, and illumination scenes. Results illustrate that multivariate models have a significantly higher accuracy than univariate models as the former provide accuracies for the canopy chlorophyll content retrieval of R² = 0.80 and Relative Root Mean Square Error (RRMSE) = 12% for the hyperspectral sensor. Random forest regression on multispectral imagery (R² > 0.9 for May, June, July, and August, and R² = 0.5 for October) and hyperspectral imagery (0.6 < R² < 0.9) led to satisfactory high and consistent accuracies for all months. Full article

Banana trees, citrus fruit trees, pome fruit trees, grapevines, mango trees, and stone fruit trees are major fruit trees cultured worldwide and correspond to nearly 90% of the global production of woody fruit trees. In light of the above, the present manuscript summarizes the viruses that infect the major fruit trees, including their taxonomy and morphology, and highlights selected viruses that significantly affect fruit production, including their genomic and biological features. The results showed that a total of 163 viruses, belonging to 45 genera classified into 23 families have been reported to infect the major woody fruit trees. It is clear that there is higher accumulation of viruses in grapevine (80/163) compared to the other fruit trees (each corresponding to less than 35/163), while only one virus species has been reported infecting mango. Most of the viruses (over 70%) infecting woody fruit trees are positive-sense single-stranded RNA (+ssRNA), and the remainder belong to the -ssRNA, ssRNA-RT, dsRNA, ssDNA and dsDNA-RT groups (each corresponding to less than 8%). Most of the viruses are icosahedral or isometric (79/163), and their diameter ranges from 16 to 80 nm with the majority being 25–30 nm. Cross-infection has occurred in a high frequency among pome and stone fruit trees, whereas no or little cross-infection has occurred among banana, citrus and grapevine. The viruses infecting woody fruit trees are mostly transmitted by vegetative propagation, grafting, and root grafting in orchards and are usually vectored by mealybug, soft scale, aphids, mites or thrips. These viruses cause adverse effects in their fruit tree hosts, inducing a wide range of symptoms and significant damage, such as reduced yield, quality, vigor and longevity. Full article