Kiwifruit Industry Research Articles

Combining Thermotherapy with Shoot Tip Culture or Cryotherapy for Improved Virus Eradication from In Vitro Actinidia macrosperma.

In recent years, kiwifruit viral diseases have become increasingly prevalent in kiwifruit-producing regions of China, significantly impacting both the yield and quality of kiwifruit. This has emerged as a significant constraint on the healthy and sustainable development of the kiwifruit industry. The use of virus-free propagation materials has been proven the most effective strategy for controlling plant viral diseases. In the present study, shoot tip culture, shoot tip cryotherapy, and their combinations with thermotherapy were established to eradicate Actinidia virus A (AcVA), Actinidia virus B (AcVB), and Actinidia chlorotic ringspot-associated virus (AcCRaV) from Actinidia macrosperma. Additionally, the impact of shoot tip size on virus eradication was evaluated. Among the three confirmed viruses, regardless of the procedure, AcVB was the easiest to eradicate, followed by AcVA and AcCRaV. Combining thermotherapy with shoot tip culture or cryotherapy resulted in a higher virus-free frequency (up to 27.3 and 50%, respectively) than shoot tip culture or cryotherapy alone (0 to 20%). Notably, the combination of thermotherapy and 0.5- to 1-mm shoot tip cryotherapy was shown to be the most effective protocol for virus eradication from A. macrosperma, which produced 50% of regenerated shoots free from all the tested viruses. To the best of our knowledge, this is the first report on virus elimination from kiwifruit infected with multiple viruses based on conventional shoot tip culture and shoot tip cryotherapy.

Two-Component Signaling System RegAB Represses Pseudomonas syringae pv. actinidiae T3SS by Directly Binding to the promoter of hrpRS1

Kiwifruit bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa), is a significant threat to the kiwifruit industry. The two-component signaling systems (TCSs) play a crucial role in regulating the virulence of Pseudomonas syringae (P. syringae), yet their specific function in Psa remains largely unclear. In this study, we found that disrupting the TCS RegAB (encoded by Psa_802/Psa_803) resulted in a notable increase in the pathogenicity of Pseudomonas syringae pv. actinidiae M228 (Psa M228) in host plant and hypersensitive reaction (HR) in nonhost plant. Through comparative transcriptome analysis of the Psa M228 wild-type strain and the regA mutant, we identified the pivotal role of RegA/B in controlling various physiological pathways, including the Type III secretion system (T3SS), a key determinant of Psa virulence. Additionally, we discovered that the RegA does have binding sites in the promoter region of the hrpR/S, and the transcriptional level of the hrpR and other T3SS-related genes increased in the regA deletion strain relative to the Psa M228 wild-type. The DNA-binding affinity of RegA, and therefore the repressor function, is enhanced by its phosphorylation. Our findings unveil the function of TCS RegAB and the regulatory mechanism of T3SS by RegAB in Psa, highlighting the diverse functions of the RegAB system.

Microbial community diversity analysis of kiwifruit pollen and identification of potential pathogens.

The kiwifruit industry typically uses commercial pollen for artificial pollination. However, during the collection of male flowers and pollen production, pollen can be easily contaminated by pathogenic bacteria that cause diseases such as canker and flower rot. Consequently, it is crucial to understand the structure of the pollen microbial community. This study employed Illumina high-throughput sequencing technology to analyze the fungal and bacterial composition in pollen samples from various regions in Shaanxi Province. Concurrently, potential pathogenic strains were isolated using traditional microbial isolation and cultivation techniques, and their molecular identification was performed through 16S rDNA sequence analysis. A tieback test was conducted on healthy branches to verify the pathogenicity of the strains. The results revealed a rich diversity of fungi and bacteria in kiwifruit pollen. At the phylum level, pollen fungi were mainly distributed in Ascomycota, and bacteria were mainly distributed in Proteobacteria and Firmicutes. The dominant fungal genera were Mycosphaerella, Aspergillus, and Cladosporium; the dominant bacterial genera were Weissella, Pantoea, Enterobacter, and Pseudomonas, respectively. Additionally, both Erwinia persicina and Pseudomonas fluorescens, isolated from pollen, exhibited high pathogenicity toward healthy kiwifruit branches. These findings contribute to a deeper understanding of the microbial diversity in commercial kiwifruit pollen used for mass pollination.

Enhancing Pseudomonas syringae pv. Actinidiae sensitivity in kiwifruit by repressing the NBS-LRR genes through miRNA-215-3p and miRNA-29-3p identification.

Kiwifruit bacterial canker, caused by Pseudomonas syringae pv. actinidiae (PSA), poses a grave threat to the global kiwifruit industry. In this study, we examined the role of microRNAs (miRNAs) in kiwifruit's response to PSA. Kiwifruit seedlings subjected to PSA treatment showed significant changes in both miRNA and gene expression compared to the control group. We identified 364 differentially expressed miRNAs (DEMs) and 7170 differentially expressed genes (DEGs). Further analysis revealed 180 miRNAs negatively regulating 641 mRNAs. Notably, two miRNAs from the miRNA482 family, miRNA-215-3p and miRNA-29-3p, were found to increase kiwifruit's sensitivity to PSA when overexpressed. These miRNAs were linked to the regulation of NBS-LRR target genes, shedding light on their role in kiwifruit's defence against PSA. This study offers insights into the miRNA482-NBS-LRR network as a crucial component in enhancing kiwifruit bioresistance to PSA infestation and provides promising candidate genes for further research.

Restricted responses of AcMYB68 and AcERF74/75 enhanced waterlogging tolerance in kiwifruit.

Most of kiwifruit cultivars (e.g. Actinidia chinensis cv. Donghong, "DH") were sensitive to waterlogging, thus, waterlogging resistant rootstocks (e.g. Actinidia valvata Dunn, "Dunn") were widely used for kiwifruit industry. Those different species provided ideal materials to understand the waterlogging responses in kiwifruit. Compared to the weaken growth and root activities in "DH", "Dunn" maintained the relative high root activities under the prolonged waterlogging. Based on comparative analysis, transcript levels of pyruvate decarboxylase (PDCs) and alcohol dehydrogenase (ADHs) showed significantly difference between these two species. Both PDCs and ADHs had been significantly increased by waterlogging in "DH", while they were only limitedly triggered by 2 days stress and subsided during the prolonged waterlogging in "Dunn". Thus, 19 differentially expressed transcript factors (DETFs) had been isolated using weighted gene co-expression network analysis combined with transcriptomics and transcript levels of PDCs and ADHs in waterlogged "DH". Among these DETFs, dual luciferase and electrophoretic mobility shift assays indicated AcMYB68 could bind to and trigger the activity of AcPDC2 promoter. The stable over-expression of AcMYB68 significantly up-regulated the transcript levels of PDCs but inhibited the plant growth, especially the roots. Moreover, the enzyme activities of PDC in 35S::AcMYB68 were significantly enhanced during the waterlogging response than that in wild type plants. Most interestingly, comparative analysis indicated that the expression patterns of AcMYB68 and the previously characterized AcERF74/75 (the direct regulator on ADHs) either showed no responses (AcMYB68 and AcERF74) or very limited response (AcERF75) in "Dunn". Taken together, the restricted responses of AcMYB68 and AcERF74/75 in "Dunn" endow its waterlogging tolerance.

Comparative genomic analyses provide insight into the pathogenicity of three Pseudomonas syringae pv. actinidiae strains from Anhui Province, China

BackgroundPseudomonas syringae pv. actinidiae (Psa) is an important bacterial plant pathogen that causes severe damage to the kiwifruit industry worldwide. Three Psa strains were recently obtained from different kiwifruit orchards in Anhui Province, China. The present study mainly focused on the variations in virulence and genome characteristics of these strains based on the pathogenicity assays and comparative genomic analyses.ResultsThree strains were identified as biovar 3 (Psa3), along with strain QSY6 showing higher virulence than JZY2 and YXH1 in pathogenicity assays. The whole genome assembly revealed that each of the three strains had a circular chromosome and a complete plasmid. The chromosome sizes ranged from 6.5 to 6.6 Mb with a GC content of approximately 58.39 to 58.46%, and a predicted number of protein-coding sequences ranging from 5,884 to 6,019. The three strains clustered tightly with 8 Psa3 reference strains in terms of average nucleotide identity (ANI), whole-genome-based phylogenetic analysis, and pangenome analysis, while they were evolutionarily distinct from other biovars (Psa1 and Psa5). Variations were observed in the repertoire of effectors of the type III secretion system among all 15 strains. Moreover, synteny analysis of the three sequenced strains revealed eight genomic regions containing 308 genes exclusively present in the highly virulent strain QSY6. Further investigation of these genes showed that 16 virulence-related genes highlight several key factors, such as effector delivery systems (type III secretion systems) and adherence (type IV pilus), which might be crucial for the virulence of QSY6.ConclusionThree Psa strains were identified and showed variant virulence in kiwifruit plant. Complete genome sequences and comparative genomic analyses further provided a theoretical basis for the potential pathogenic factors responsible for kiwifruit bacterial canker.

Harnessing the bacteriophages to deal with canker infection of kiwi fruit: challenges and future perspective

The worldwide kiwifruit industry has suffered significant economic losses in recent decades as a result of the destructive bacterial plant disease Pseudomonas syringae pv. actinidiae (Psa). Existing control approaches, which depend on the use of copper bactericides and antibiotics, are facing growing challenges due to the rise of resistance to antibiotics and ecological issues. Although biocontrol techniques show promise in laboratory settings, their efficacy in real-world field situations remains unclear. In order to tackle this issue, the emergence of a phage-based biocontrol method becomes a vital alternative, considering the precise targeting of bacteriophages (phages) towards the particular bacteria and their ecologically benign characteristics. This thorough assessment commences by delineating the repercussions of Psa-induced kiwifruit canker, underscoring the need for pioneering management strategies. The text explores the many types and strengths of Psa strains, and then shifts its attention to recent progress in the identification and description of Psa phages. The main topics discussed are the physical structure of phages, the spectrum of organisms they may infect, their ability to destroy bacterial cells, the study of their genetic material, and the process by which they break down bacterial cells. The review examines biocontrol tactics and their possible obstacles in kiwifruit orchards, specifically focusing on abiotic variables such as elevated temperature, UV irradiation and severe pH. The manuscript highlights the crucial importance of phages in efficiently controlling Psa infections, providing a sustainable and focused approach for safeguarding plants.

Streptothricin-F Inhibition of FtsZ Function: A Promising Approach for Controlling Pseudomonas syringae pv. actinidiae.

Pseudomonas syringae pv. actinidiae (Psa) is a significant pathogenic bacterium affecting the kiwifruit industry. This study investigated the target sites of streptothricin-F (ST-F), produced by Streptomyces lavendulae gCLA4. The inhibition of ST-F on Psa was examined by the microscopic structural differences of Psa before and after treatment with ST-F, as well as the interaction between ST-F and cell division-related proteins. The results revealed filamentation of Psa after ST-F treatment, and fluorescence microscopy showed that ST-F inhibited the formation of the Z-ring composed of FtsZ protein. In vitro experiments and molecular docking demonstrated that ST-F can bind to FtsZ with a binding energy of 0.4 μM and inhibit FtsZ's GTP-dependent polymerization reaction. In addition, ST-F does not exert inhibitory effects on cell division in Psa strains overexpressing ftsZ. In conclusion, FtsZ is one of the target sites for ST-F inhibition of Psa, highlighting its potential as a therapeutic target for controlling Psa-induced kiwifruit bacterial canker.

Enhancing kiwifruit flower pollination detection through frequency domain feature fusion: a novel approach to agricultural monitoring.

The pollination process of kiwifruit flowers plays a crucial role in kiwifruit yield. Achieving accurate and rapid identification of the four stages of kiwifruit flowers is essential for enhancing pollination efficiency. In this study, to improve the efficiency of kiwifruit pollination, we propose a novel full-stage kiwifruit flower pollination detection algorithm named KIWI-YOLO, based on the fusion of frequency-domain features. Our algorithm leverages frequency-domain and spatial-domain information to improve recognition of contour-detailed features and integrates decision-making with contextual information. Additionally, we incorporate the Bi-Level Routing Attention (BRA) mechanism with C3 to enhance the algorithm's focus on critical areas, resulting in accurate, lightweight, and fast detection. The algorithm achieves a of 91.6% with only 1.8M parameters, the AP of the Female class and the Male class reaches 95% and 93.5%, which is an improvement of 3.8%, 1.2%, and 6.2% compared with the original algorithm. Furthermore, the Recall and F1-score of the algorithm are enhanced by 5.5% and 3.1%, respectively. Moreover, our model demonstrates significant advantages in detection speed, taking only 0.016s to process an image. The experimental results show that the algorithmic model proposed in this study can better assist the pollination of kiwifruit in the process of precision agriculture production and help the development of the kiwifruit industry.

Occurrence of Kiwifruit Vine Decline Syndrome and Its Prevention Using Rootstock Tolerant to Waterlogging

Kiwifruit industry has been threatened by the emergence of kiwifruit vine decline syndrome causing plant death within one or two years from symptom appearance. The main symptoms of this syndrome are root cortex breakdown, leaf necrosis, phylloptosis, fruit skin wrinkling, and twig wilting. Kiwifruit vine decline syndrome occurred on both <i>Actinidia chinensis</i> var. <i>chinensis</i> and <i>A. chinensis</i> var. <i>deliciosa</i> in mid-summer after rainy season. Kiwifruit vine decline syndrome was turned out to be severely occurred in wettable clay soils affected by waterlogging or poor aeration. No pathogens were directly correlated with the syndrome. Kiwifruit vine decline syndrome could be expected to be efficiently prevented controlled using Bounty 71 rootstock tolerant to water stress such as waterlogging.

Investigating systemic and social dynamics of food loss and waste: An application of waste regime theory to food production in Aotearoa New Zealand

This research investigates the relationships of social and discursive effects on food loss and waste (FLW) in primary food production through a case study of the kiwifruit industry in Aotearoa New Zealand by using ‘waste regime theory’, which was first developed by Science and Technology Studies scholar Zsuzsa Gille as an organising concept. Qualitative data from semi-structured interviews and analysis of industry and policy documents are interpreted through thematic analysis to explore the production, politics and representation of FLW, and to demonstrate the ways in which these factors interact to enact a ‘food waste regime’. The findings identify two distinct discourses of FLW: either as consequence of supply chain dynamics, or as a consequence of market driven quality assurance (QA) requirements. The former is seen as opening possibilities for technical interventions. The other is seen to be a baked-in structural reality of the industry that doesn’t allow for any strategic intervention. Either discourse arguably has the effect of invisibilising different aspects of FLW in the sector and potentially reducing the perceived need interventions by managers at a systemic level in the sector.

A 4D Proteome Investigation of the Potential Mechanisms of SA in Triggering Resistance in Kiwifruit to Pseudomonas syringae pv. actinidiae.

Kiwifruit bacterial cankers caused by Pseudomonas syringae pv. actinidiae (Psa) are a serious threat to the kiwifruit industry. Salicylic acid (SA) regulates plant defense responses and was previously found to enhance kiwifruit's resistance to Psa. However, the underlying mechanisms of this process remain unclear. In this study, we used 4D proteomics to investigate how SA enhances kiwifruit's resistance to Psa and found that both SA treatment and Psa infection induced dramatic changes in the proteomic pattern of kiwifruit. Psa infection triggered the activation of numerous resistance events, including the MAPK cascade, phenylpropanoid biosynthesis, and hormone signaling transduction. In most cases, the differential expression of a number of genes involved in the SA signaling pathway played a significant role in kiwifruit's responses to Psa. Moreover, SA treatment upregulated numerous resistance-related proteins, which functioned in defense responses to Psa, including phenylpropanoid biosynthesis, the MAPK cascade, and the upregulation of pathogenesis-related proteins. We also found that SA treatment could facilitate timely defense responses to Psa infection and enhance the activation of defense responses that were downregulated in kiwifruit during infection with Psa. Thus, our research deciphered the potential mechanisms of SA in promoting Psa resistance in kiwifruit and can provide a basis for the use of SA to enhance kiwifruit resistance and effectively control the occurrence of kiwifruit bacterial cankers.

Grasping perception and prediction model of kiwifruit firmness based on flexible sensing claw

Fruit firmness is an important quality indicator that affects fruit storage and transportation. Robot automation sorting is becoming a trend in fruit detection and sorting. During the kiwifruit picking and feeding stages, a non-destructive tool was developed that utilizes flexible claws to grasp and sense the firmness of the kiwifruit. This innovative tool aims to enhance the level of intelligence within the kiwifruit industry. In this study, a flexible sensing claw was designed for grasping and perceiving kiwifruit firmness with force sensors and bending sensors. According to the force–deformation law of flexible claw in the process of grasping kiwifruit, a tactile-based firmness index H based on the flexible sensing claw with fruit as six elements Kelvin-Burgers coupling was innovatively proposed as a reference index for firmness prediction. The correlation between the tactile-based firmness index of flexible sensing claw and the reference firmness of kiwifruit was analyzed by creep and puncture tests. Finally, the firmness date and grasping data of 210 kiwifruits were collected experimentally during different storage periods. The tactile-based firmness index of flexible claw can effectively distinguish kiwifruit with different firmness through comparative analysis. And the regression model achieved an approximate prediction for kiwifruit firmness in the external prediction set (RP2 = 0.813, REMEP=0.369 N/mm, RPDP=2.342). The flexible sensing claw system established in this study can characterize the firmness of kiwifruit during picking and placing the fruit.

Study on the mechanism of local compression bruising in kiwifruit based on FEM

AbstractThis study focuses on the relationship between local compression and local bruise volume of kiwifruits by means of finite element method (FEM). The effects of four indenter shapes and three compression directions on the local kiwifruit bruise were considered. The local bruise volume and the irregular cross section area of kiwifruit were calculated. Multi‐scale kiwifruit 3D modelling based on irregular cross‐sectional area computed by slice‐integration method. Local compression bruise was simulated by FEM. The results of the local bruise test show that the contact force and the bruise volume of kiwifruit are positive linear correlation. Comparing the simulation with the experimental, the mean absolute percentage error (MAPE) of the reconstructed model is 0.0394, and the R2 of contact force–bruise volume curve is 0.8203. The maximum equivalent forces and abrasions occur in the 0° and 90° loading directions with the square indenter has been showed by FEM results.Practical applicationsSe‐enriched kiwifruit has high nutrition and economic value. Kiwifruits are often influenced by a variety of factors and processes from harvest to consumption time. Cleaning, transport, and various processing operations including peeling and slicing in the kiwifruit industry are responsible for local bruise to kiwifruit. Therefore, understanding the mechanism of local bruise caused by local contact force of kiwifruit plays an important role in reducing kiwifruit waste in the postharvest stage. Local bruise mechanisms can be used in harvesting and post‐harvest mechanical design and product transportation and positioning equipment.

Identification and genetic characterization of Pseudomonas syringae pv. actinidiae from kiwifruit in Sichuan, China.

Pseudomonas syringae pv. actinidiae (Psa) causes kiwifruit bacterial canker and poses a major threat to the kiwifruit industry. This study aimed to investigate the genetic characteristics of the Psa population from kiwifruit in Sichuan, China. Sixty-seven isolates obtained from diseased plants were characterized using morphological features, multiplex-PCR and multilocus sequence analysis (MLSA). The isolates exhibited the typical colony morphology of Psa. Multiplex PCR amplification identified every isolate as Psa biovar 3. MLSA analysis of the three housekeeping genes gapA, gyrB, and pfk, revealed that the reference strains of the five described biovars were clearly distinguished by a combined phylogenetic tree, and all the tested isolates clustered with the reference strains of Psa biovar 3. Through a phylogenetic tree constructed from a single gene, it was found that pkf gene alone could distinguish biovar 3 from the other biovars. Furthermore, all Psa isolates analyzed by BOX-A1R-based repetitive extragenic palindromic (BOX)-PCR and enterobacterial repetitive intergenic consensus (ERIC)-PCR clustered into four groups. The clustering results of BOX- and ERIC-PCR indicated that group III had the largest number of isolates, accounting for 56.72% and 61.19% of all sixty-seven isolates, respectively, and the two characterization methods were similar and complementary. The results of this study revealed that the genomes of Psa isolates from Sichuan had rich genetic diversity, but no obvious correlation was found between clustering and geographical region. This research provides novel methodologies for rapidly detecting kiwifruit bacterial canker pathogen and a molecular differentiation at genetic level of Psa biovars diversity in China.

Genetic diversity of Actinidia spp. shapes the oomycete pattern associated with Kiwifruit Vine Decline Syndrome (KVDS)

Kiwifruit Vine Decline Syndrome (KVDS) is an important soil-borne disease for the Italian kiwifruit industry, causing €300,000 in economic losses in 2020 alone. So far, the organisms recognized as involved in the aetiology of KVDS mainly belong to the Oomycota. As no effective management strategies exist, a promising approach to overcoming KVDS is the use of resistant species as rootstocks or for inclusion in breeding programs. Several Actinidia genotypes showing different level of resistance to KVDS were grown in disease-promoting soils. A metabarcoding approach was set up to identify KVDS-associated oomycetes and investigate whether the main species involved may vary according to plant genotype. Our results clearly showed significant differences between the genotypes in terms of oomycetes present in both plant rhizosphere and endosphere, which were strongly correlated with the symptoms displayed. We found out that the resistance of Actinidia macrosperma to KVDS is related to its ability to shape the pathobiome, particularly as far as the endosphere is concerned. In our conditions, Phytophthora sp. was predominantly found in sensitive genotypes, whilst Globisporangium intermedium was mainly detected in asymptomatic plants, suggesting that the latter species could compete with the recruitment of Phytophthora sp. in plants with different levels of resistance, consequently, explaining the onset of symptoms and the resistance condition.

Paenibacillus polymyxa YLC1: A promising antagonistic strain for biocontrol of Pseudomonas syringae pv. actinidiae, causing kiwifruit bacterial canker.

Kiwifruit bacterial canker (KBC) caused by Pseudomonas syringae pv. actinidiae (Psa) is the main limiting factor in the kiwifruit industry. This study aimed to identify bacterial strains with antagonistic activity against Psa, analyze antagonistically active substances, and provide a new basis for the biological control of KBC. A total of 142 microorganisms were isolated from the rhizosphere soil of asymptomatic kiwifruit. Among them, an antagonistic bacterial strain was identified as Paenibacillus polymyxa YLC1 by 16S rRNA sequencing. KBC control by strain YLC1 (85.4%) was comparable to copper hydroxide treatment (81.8%) under laboratory conditions and field testing. Active substances of strain YLC1 were identified by genetic sequence analysis using antiSMASH. The six biosynthetic active compound gene clusters that were identified as encoding ester peptide synthesis, such as polymyxins. An active fraction was purified and identified as polymyxin B1 using chromatography, hydrogen nuclear magnetic resonance (NMR), and liquid chromatography-mass spectrometry. In addition, polymyxin B1 was also found significantly to suppressed the expression of T3SS-related genes but did not affect the growth of Psa at low concentrations. In this study, a biocontrol strain P. polymyxa YLC1 obtained from kiwifruit rhizosphere soil exhibited excellent control effects on KBC in vitro and in field tests. Its active compound was identified as polymyxin B1, which inhibits a variety of pathogenic bacteria. We conclude that P. polymyxa YLC1 is a biocontrol strain with excellent prospects for development and application. This article is protected by copyright. All rights reserved.

Molecular Mechanism of miR160d in Regulating Kiwifruit Resistance to Botrytis cinerea.

Gray mold caused by Botrytis cinerea leads to huge economic losses to the kiwifruit (Actinidia chinensis) industry. Elucidating the molecular mechanism responding to B. cinerea is the theoretical basis for the resistance to molecular breeding of kiwifruit. Previous studies have shown that miR160 regulates plant disease resistance through the indole-3-acetic acid (IAA) signaling pathway. In this study, kiwifruit "Hongyang" was used as the material, and Ac-miR160d and its target genes were identified and cloned. Overexpression and virus-induced gene silencing (VIGS) technology combined with RNA-seq were adopted to analyze the regulatory role of Ac-miR160d in kiwifruit resistance to B. cinerea. Silencing Ac-miR160d (AcMIR160d-KN) increased kiwifruit sensitivity to B. cinerea, whereas overexpression of Ac-miR160d (AcMIR160d-OE) increased kiwifruit resistance to B. cinerea, suggesting that Ac-miR160d positively regulates kiwifruit resistance to B. cinerea. In addition, overexpression of Ac-miR160d in kiwifruit increased antioxidant enzyme activities, such as catalase (CAT) and superoxide dismutase (SOD), and endogenous phytohormone IAA and salicylic acid (SA) content, in response to B. cinerea-induced stress. RNA-seq identified 480 and 858 unique differentially expressed genes in the AcMIR160d-KN vs CK and AcMIR160d-OE vs CK groups, respectively, with fold change ≥2 and false discovery rate <0.01. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that families associated with "biosynthesis of secondary metabolites" are possibly regulated by Ac-miR160d. "Phenylpropanoid biosynthesis", "flavonoid biosynthesis", and "terpenoid backbone biosynthesis" were further activated in the two comparison groups upon B. cinerea infection. Our results may reveal the molecular mechanism by which miR160d regulates kiwifruit resistance to B. cinerea and may provide gene resources for molecular breeding in kiwifruit resistance.

Chemical composition changes of kiwifruit petiole cell walls infected by Pseudomonas syringae pv. actinidiae based on confocal Raman imaging combined with chemometrics

Kiwifruit canker caused by Pseudomonas syringae pv. actinidiae (Psa) is devastating to the kiwifruit industry. Because of the complex pathogenesis of kiwifruit canker, there is still a lack of effective control measures. The aim of this study was to characterize the temporal and spatial changes of biopolymers in the petiole cell walls of healthy and cankered kiwifruit using confocal Raman microscopy (CRM) techniques combined with Chemometrics. We proposed a general investigation of the development of kiwifruit canker and chemical distribution imaging was successfully applied to the analysis of disease dynamics. First, Raman spectra (RS) of healthy and diseased kiwifruit petiole cell walls were acquired at a micron-scale spatial resolution, followed by label-free in situ imaging of the cell wall. The results of RS and chemical imaging showed that the changes of cellulose and lignin on the petiole cell wall of susceptible kiwifruit under Psa stress were time-dependent, and the degradation rate of cellulose and lignin reached about 25% after eight days of incubation. The results of principal component analysis (PCA) and support vector machine (SVM) based on RS showed that healthy, early-stage disease and late-stage disease samples exhibited significant clustering effects and the SVM classification accuracy was as high as 100%. The multivariate curve resolved–alternating least squares (MCR–ALS) is used to optimize the Raman imaging in order to eliminate the noise and interference caused by the peak clamping method and provide a meaningful chemical profile. In conclusion, CRM combined with chemical classification algorithms and imaging analysis has certain feasibility and application prospects in the early warning and cellular-level dynamic characterization of kiwifruit canker.

Antibacterial Metabolites from Kiwi Endophytic Fungus Fusarium tricinctum, a Potential Biocontrol Strain for Kiwi Canker Disease

Pseudomonas syringae pv. actinidiae (Psa) is a Gram-negative bacterium causing the kiwifruit canker disease, resulting in serious economic losses to the kiwifruit industry. This study investigated the use of an endophytic fungus, Fusarium tricinctum, obtained from the kiwi plant (Actinidia chinesis) as a potential biocontrol strain against the Psa. F. tricinctum showed an inhibition rate of 59.5% in vitro against Psa. Bioassay-guided isolation was conducted on the cultural broth of F. tricinctum and seven new imidazole alkaloids, (±)-fusaritricine J ((±)-1) and fusaritricines K-P (2-7), and four enniatins (8-11) were identified. Their absolute configurations were established through extensive spectroscopic methods, quantum chemical calculations, and X-ray single crystal diffraction. Compounds 1, 4, 5, and 8-11 showed comparable anti-bacterial activities against Psa as positive control, with MIC values of 25-50 μg/mL. Further cell membrane permeability assay suggested that the most active compound 4 could destroy the bacterial cell wall structure. Hence, F. tricinctum metabolites could be applied as potential anti-Psa agents, and F. tricinctum could be considered a biocontrol strain for the control of the kiwifruit canker disease.