Kiwifruit Plants Research Articles

Amendment with biocontrol strains increases Trichoderma numbers in mature kiwifruit (Actinidia chinensis) orchard soils for up to six months after application

A Trichoderma mixture was applied to kiwifruit plants in a pot experiment and to mature orchard vines to determine its effect on numbers of root-associated fungi and compare application methods into kiwifruit orchards in New Zealand. Trichoderma and other fungal numbers were recorded using a root plating technique. In the pot experiment, a significantly greater number of Trichoderma was isolated from treated compared to untreated plants 6 and 10 weeks after inoculation. Six months after application, greater numbers of Trichoderma were recovered in the orchards from Trichoderma treated vines and the increase was comparable for all application methods with over 50% of isolated fungi identified as Trichoderma compared to 33% in the water-only control. Different viable methods are available that can easily be integrated into everyday orchard management in order to introduce Trichoderma into mature kiwifruit stands. A six-monthly or more frequent application schedule seems advisable.

Delivery systems for agriculture: Fe-EDDHSA/CaCO3 hybrid crystals as adjuvants for prevention of iron chlorosis.

Fe-EDDHSA/CaCO3 hybrid crystals are synthesized and tested in vitro to determine their effect in treating iron chlorosis in kiwifruit plants, used as a proof of concept. Under the alkaline conditions provided by the calcareous substrate, plants release protons that dissolve the hybrids and trigger Fe uptake. These CaCO3 hybrids represent a new system for active molecule delivery in agriculture.

Circular RNAs and Plant Stress Responses.

Circular RNAs (circRNAs) are a novel class of noncoding RNAs that have been extensively explored in the past few years. The advent of new high-throughput sequencing technologies coupled with bioinformatics tools revealed the presence of these molecules in the transcriptome of a wide range of organisms. In animals, circRNAs can modulate gene expression and act as sponges of miRNAsto inhibit their activity. It has been demonstrated that they have the potential to be diagnostic biomarkers as their expression is closely associated to human diseases, such as Alzheimer and cancer. However, in plants their function remains elusive. Recently, the role of the circRNAs in plant stress responses has been studied. During the infection of Pseudomonas syringae in kiwifruit plants, 584 circRNAs were differentially expressed in leaf samples, and a group of them could be further associated with the stage of infection. Under phosphate deficiency conditions, 27 rice circRNAs were reported to be differentially expressed. In tomato, 163 circRNAs demonstrated chilling-responsive expression, with 102 containing miRNA-binding sitesand are predicted to act as miRNA sponges. Additionally,Arabidopsis seedlingspresented 1583 heat-specific circRNAs, and it was alsoreported that heat stress could increase the quantity, length, and alternative circularization events of circRNAs. Finally, wheat seedlingsunder dehydration stress had 62 circRNAs differentially expressed, with 6 being predicted as miRNA sponges. Although the role of plant circRNAs during the biotic and abiotic stresses is still poorly characterised, these molecules have the potential to expand the number of targets and tools in the biotechnologyfield.

Molecular characterization of an Apple stem grooving virus isolate from kiwifruit (Actinidia chinensis) in China

Apple stem grooving virus (ASGV) is the type species of the genus Capillovirus in the family Betaflexiviridae. The virus naturally infects several important horticultural crops. Although many ASGV isolates from apple (Malus spp.), pear (Pyrus spp.), citrus (Citrus spp.) and lily (Lilium spp.) have been characterized, the occurrence status and molecular characteristics of the virus from kiwifruit trees are still largely unknown. In this study, by employing the strategy of small RNA deep sequencing coupled with conventional RT-PCR, we provide the first complete genome sequence of an ASGV isolate (named ASGV-Ac) infecting a kiwifruit plant (Actinidia chinensis) grown in China. The complete genome of ASGV-Ac consisted of 6496 nucleotides, excluding poly (A) tail at its 3ʹ end. ASGV-Ac shared high nucleotide sequence identities of 96.9% and 93.5% with a kiwifruit ASGV isolate reported from New Zealand (accession no. AF522459) for their CP and MP coding regions. However, the isolate was phylogenetically distal to ASGV isolates from all other hosts by sharing 79.5–82.4% genome sequence identity, and likely represented a novel variant. RT-PCR detection revealed the presence of ASGV-infected kiwifruit in two provinces in China. The partial CP gene of nine ASGV isolates determined in this study shared 87.8–99.6% nucleotide sequence identity with the corresponding sequences of other reported ASGV isolates from kiwifruit, indicating molecular diversity of ASGV isolates from kiwifruit plants. This study provides important evidence for monitoring the viral disease and novel molecular information for developing efficient detection techniques to prevent virus spread.

Optimization of propagation techniques and timimg for the production of kiwi fruit (Actinidia chinensis) plant at Khyber pakhtun khwa Mingora Swat

Optimization of propagation techniques and timimg for the production of kiwi fruit (Actinidia chinensis) plant at Khyber pakhtun khwa Mingora Swat

Xanthomonas arboricola pv. fragariae: a confirmation of the pathogenicity of the pathotype strain

Xanthomonas arboricola pv. fragariae is the causal agent of strawberry bacterial leaf blight, and, so far, has been reported in Italy and Turkey. Some years later the description of this new pathovar, and its pathogenicity, was questioned based upon artificial inoculations performed with some strains of the pathogen, including the pathotype strain; it was concluded that it is a non-pathogenic xanthomonad. This notion has also been accepted in other studies aiming at elucidating the molecular characteristics of X. arboricola strains. In the present investigation, we performed again pathogenicity tests using the pathotype strain of X. a. pv. fragariae, namely PD 2780 = LMG 19145 = CFBP 6771, by a spray leaf inoculation technique on strawberry cultivars Candonga, Sabrina and Murano. Similarly, it was also inoculated onto pot-cultivated walnut, hazelnut, peach, apple and kiwifruit plants. All typical symptoms of bacterial leaf blight of strawberry were observed within 25 days after the artificial inoculation on all tested strawberry cultivars. None of the other plant species showed symptoms of disease. We conclude again that the pathotype strain of X. a. pv. fragariae is a pathogenic bacterium. This technique also allowed us to observe typical symptoms of strawberry bacterial blight in a shorter time than that obtained previously by puncturing the major vein of the three leaflets of the leaf.

Whole transcriptome sequencing of Pseudomonas syringae pv. actinidiae-infected kiwifruit plants reveals species-specific interaction between long non-coding RNA and coding genes

An outbreak of kiwifruit bacterial canker disease caused by Pseudomonas syringae pv. actinidiae (Psa) beginning in 2008 caused disaster to the kiwifruit industry. However the mechanisms of interaction between kiwifruit and Psa are unknown. Long noncoding RNAs (lncRNAs) are known to regulate many biological processes, but comprehensive repertoires of kiwifruit lncRNAs and their effects on the interaction between kiwifruit and Psa are unknown. Here, based on in-depth transcriptomic analysis of four kiwifruit materials at three stages of infection with Psa, we identified 14,845 transcripts from 12,280 loci as putative lncRNAs. Hierarchical clustering analysis of differentially-expressed transcripts reveals that both protein-coding and lncRNA transcripts are expressed species-specifically. Comparing differentially-expressed transcripts from different species, variations in pattern-triggered immunity (PTI) were the main causes of species-specific responses to infection by Psa. Using weighted gene co-expression network analysis, we identified species-specific expressed key lncRNAs which were closely related to plant immune response and signal transduction. Our results illustrate that different kiwifruit species employ multiple different plant immunity layers to fight against Psa infection, which causes distinct responses. We also discovered that lncRNAs might affect kiwifruit responses to Psa infection, indicating that both protein-coding regions and noncoding regions can affect kiwifruit response to Psa infection.

Microparticles containing gallic and ellagic acids for the biological control of bacterial diseases of kiwifruit plants

Over the last decades, kiwifruit cultivation has gained increasing importance all over the world, but some bacterial diseases seriously threaten its cultivation. The most dangerous one is the bacterial canker caused by Pseudomonas syringae pv. actinidiae Takikawa et al., but also floral bud necrosis by Pseudomonas syringae pv. syringae van Hall and bacterial blight by Pseudomonas viridiflava (Burkholder) Dowson affect kiwifruit plants. Their control relies mainly on antibiotics, where allowed, and copper, although this adversely affects the environment, so that alternative control measures are needed. Here we investigate gallic acid and ellagic acid, substances easily obtainable from some plant tissues, for their antimicrobial activity aiming to use them as support in the biocontrol of kiwifruit bacterial diseases. These active principles demonstrated their effectiveness as pure substances in both in vitro and in vivo tests. Moreover, their encapsulation in methacrylate polymeric microparticles showed to improve their usefulness and to prolong remarkably their activity up to 14 days after the treatment, when applied in greenhouse or in field on artificially and naturally infected plants, respectively. The encouraging results obtained by this type of microformulation point the way to future alternative biological control strategies against kiwifruit bacterial diseases.

Draft Genome Sequences of Pectobacterium carotovorum subsp. actinidiae ICMP 19971 and ICMP 19972, Two Strains Isolated from Actinidia chinensis with Symptoms of Summer Canker in South Korea.

ABSTRACTPectobacterium carotovorum subsp. actinidiae is the causal agent of summer canker in kiwifruit plants in South Korea. We report here the draft genome sequences of two P. carotovorum subsp. actinidiae strains, ICMP 19971 and ICMP 19972, which were originally isolated from Actinidia chinensis with symptoms of summer canker. These genome sequences will aid in the identification of genetic traits associated with their unusual capacity to cause canker and help understanding of the threat these exotic enterobacteria pose to the New Zealand kiwifruit industry.

Identification of Loci of Pseudomonas syringae pv. actinidiae Involved in Lipolytic Activity and Their Role in Colonization of Kiwifruit Leaves.

Bacterial canker disease caused by Pseudomonas syringae pv. actinidiae, an emerging pathogen of kiwifruit plants, has recently brought about major economic losses worldwide. Genetic studies on virulence functions of P. syringae pv. actinidiae have not yet been reported and there is little experimental data regarding bacterial genes involved in pathogenesis. In this study, we performed a genetic screen in order to identify transposon mutants altered in the lipolytic activity because it is known that mechanisms of regulation, production, and secretion of enzymes often play crucial roles in virulence of plant pathogens. We aimed to identify the set of secretion and global regulatory loci that control lipolytic activity and also play important roles in in planta fitness. Our screen for altered lipolytic activity phenotype identified a total of 58 Tn5 transposon mutants. Mapping all these Tn5 mutants revealed that the transposons were inserted in genes that play roles in cell division, chemotaxis, metabolism, movement, recombination, regulation, signal transduction, and transport as well as a few unknown functions. Several of these identified P. syringae pv. actinidiae Tn5 mutants, notably the functions affected in phosphomannomutase AlgC, lipid A biosynthesis acyltransferase, glutamate-cysteine ligase, and the type IV pilus protein PilI, were also found affected in in planta survival and/or growth in kiwifruit plants. The results of the genetic screen and identification of novel loci involved in in planta fitness of P. syringae pv. actinidiae are presented and discussed.

Identification and expression analysis of photoreceptor genes in kiwifruit leaves under natural daylength conditions and their relationship with other genes that regulate photoperiodic flowering

Kiwifruit (Actinidia chinensis var. deliciosa (A. Chev) A. Chev.) is a dioecious vine highly dependent on pollination, which is limited by a lack of synchrony of flowering time between male and female plants. In many plant species, the regulation of the timing of flowering depends largely on seasonal cues such as photoperiod, which is detected by photoreceptors. In this report, we determined the full sequences of the PHYB (AcPHYB) and PHYA (AcPHYA) genes and a partial sequence of the CRY2 (AcCRY2) gene in kiwifruit. Next, we monitored the expression patterns of these photoreceptor genes (AcPHYA, AcPHYB and AcCRY2) as well as other genes involved in flowering regulation (AcCO-like and AcFT) in the leaves of kiwifruit plants grown under natural photoperiods in the field. The annual expression patterns of AcPHYB, AcPHYA and AcCRY2 genes showed that they were significantly highly expressed from late flower development until full bloom and fitting with floral evocation, closely matching the peaks of expression detected for the AcFT and AcCO-like genes. In addition, the daily expression patterns of AcPHYB, AcPHYA and AcCRY2 were analyzed in leaves collected under different daylength conditions. Under long-day (LD) conditions, maximum expression levels were detected in the middle of the day in April (before full bloom), while their expression lost their daily rhythmic patterns in June (after full bloom) and were consistently expressed at low levels. Under short-day (SD) conditions, AcPHYB, AcPHYA and AcCRY2 gene expression patterns were the opposite of those observed in April. With respect to AcFT, no expression was detected in SD conditions. In contrast, the AcCO-like gene oscillated for all daylength conditions with the same daily rhythm. Our results seem to indicate the involvement of photoreceptor genes in kiwifruit flowering regulation. The different daily expression patterns detected for AcPHYA, AcPHYB, AcCRY2 and AcFT under different daylength conditions suggest that photoperiod regulates their expression, while the uniform expression of the AcCO-like gene is in agreement with its reported regulation by the circadian clock.

Genetic variability suggests that three populations of Ceratocystis fimbriata are responsible for the Ceratocystis wilt epidemic on kiwifruit in Brazil

Ceratocystis fimbriata is a native, soilborne pathogen in South America that causes a lethal wilt disease on a broad range of economically important plants. Ceratocystis wilt on kiwifruit (Actinidia spp.) was first recognized in 2010 in the state of Rio Grande do Sul, Brazil. The genetic variation among kiwifruit isolates was analized to determine if a single introduced strain of the pathogen was responsible for the epidemic or if there was substantial genetic variation in the population, suggesting that the fungus was soilborne and indigenous to the region. We used 14 microsatellite (simple sequence repeat, SSR) markers to identify 18 genotypes of C. fimbriata among 76 isolates from eight kiwifruit farms. The 18 genotypes clustered into three groups based on UPGMA analysis of the microsatellite alleles. The largest group comprised 60 isolates of 11 closely-related microsatellite genotypes obtained from seven of the eight farms. These genotypes appeared to have originated from a single farm that had supplied cuttings for grafting to the other farms. The population of the pathogen from the farm that supplied the cuttings had the highest level of genotypic diversity and relatively high gene diversity, suggesting that this source population represented an indigenous, soilborne population. Phylogenetic analyses of the DNA sequences of the mating type locus (including portions of MAT1-1-2 and MAT1-2-1) placed the isolates into three groups, corresponding to the three microsatellite groups. Most of the isolates, including all the tested isolates from the farm that supplied the cuttings, had mating type gene sequences that were distinct from other Brazilian populations of C. fimbriata. A second group comprised isolates from one farm that had mating type gene sequences typical of Mata Atlântica (Rio de Janeiro and Sao Paulo) populations of C. fimbriata on Colocasia esculenta and Mangifera indica. Three farms purchased kiwifruit plants or rootstocks from commercial nurseries in Brazil as well as scions from the source farm, and some of the isolates from these farms were genetically similar to Eucalyptus isolates of C. fimbriata from Bahia and Minas Gerais, Brazil. The kiwifruit epidemic in Rio Grande do Sul is the southern-most report of C. fimbriata in Brazil, and the primary pathogen population on kiwifruit appears to be indigenous and originated from a single farm that distributed the pathogen in grafting material. In addition, commercial nursery stock was also implicated as sources of C. fimbriata genotypes. The disease is a major limiting factor for kiwifruit production in southern Brazil, and the results suggest that clean planting stock will be important to successful production.

Effects of Stored Pollens from Wild <i>Actinidia eriantha</i> Vines on Some Fruit Quality Traits

Our study was conducted to determine In vitro germination ability of pollens from 25 wild Actinidia eriantha genotypes after one year freeze storage, afterwards we examined fertilization ability of stored pollens of 8 genotypes selected according to In vitro test results from aforementioned 25 genotypes, and finally investigated effects of stored viable pollens from “MH67”, “MH55”, “MH48” and “MH45” genotypes on fruit quality characters of the female experimental plant “M3” as the main purpose. Non-pollinated “M3” kiwifruit plant was taken as control. We found that In vitro germination and fertilization ability of different stored pollen sources, and also fruit quality characters including dry matter, total sugar, titratable acid, vitamin C, total polyphenol, total flavonoid, chlorophyll (“a”, “b”, and total) and carotenoid contents except total soluble solid content were significantly different. MH67 and MH45 genotypes were evaluated as the most suitable pollenizers which can be recommended as new candidate cultivars because of long term storage ability and brought about desired fruit quality characters. They also will be investigated more at further breeding studies.

Erratum to: Enhancement of PR1 and PR5 gene expressions by chitosan treatment in kiwifruit plants inoculated with Pseudomonas syringae pv. actinidiae

Erratum to: Enhancement of PR1 and PR5 gene expressions by chitosan treatment in kiwifruit plants inoculated with Pseudomonas syringae pv. actinidiae

Enhancement of PR1 and PR5 gene expressions by chitosan treatment in kiwifruit plants inoculated with Pseudomonas syringae pv. actinidiae

Kiwifruit, with a production of more than 1.5 million tons/year in the world, must be protected against attack by its most common pathogen. Following the European guidelines on the substitution of pesticides by safer alternatives, the aim of this work was to verify if kiwifruit plants are able to better resist pathogen infections through the use of chitosan, a biodegradable compound and a well-known elicitor of Systemic Acquired Resistance (SAR). To evaluate the chitosan’s elicitation effect in plant during the treatment period, two genes involved in the metabolic pathway of SAR were chosen, Pathogenesis Related Protein 1 and 5 (PRs). Primers for both genes were designed and validated and chitosan’s elicitation effect was tested in qRT-PCR. Elicitation of SAR was first evaluated in a model system with plants cultured in vitro and subsequently in 2 year old plants belonging to two different species (Actinidia chinensis Planch. and A. deliciosa (A. Chev.) C.F. Liang & A.R. Ferguson). To evaluate the effects of chitosan elicitation in the presence of the pathogen attack, the 2-year-old plants were inoculated with the bacterium Pseudomonas syringae pv. actinidiae. Micropropagated kiwifruit plants were a good model to test molecular markers for SAR onset. Moreover, PR1 and PR5 have also shown to be suitable candidates for the detection of the plant immune system activation. In this study, chitosan elicited a systemic response in kiwi plants with intensity comparable to other well-known signalling compounds (salicylic acid, methyl jasmonate or ethylene), as shown by the changes in PR1’s and PR5’s transcription profiles. The data obtained by chitosan treatments in in vitro cultures were confirmed in plants grown in greenhouse, in which, moreover, the combination of chitosan treatment and the bacterial inoculum had the greatest effect on PRs synthesis. This study also proved that chitosan, leading to an increased expression of both PRs, has a role in kiwifruit defense reactions.

Actinidia chlorotic ringspot-associated virus: a novel emaravirus infecting kiwifruit plants.

By integrating next-generation sequencing (NGS), bioinformatics, electron microscopy and conventional molecular biology tools, a new virus infecting kiwifruit vines has been identified and characterized. Being associated with double-membrane-bound bodies in infected tissues and having a genome composed of RNA segments, each one containing a single open reading frame in negative polarity, this virus shows the typical features of members of the genus Emaravirus. Five genomic RNA segments were identified. Additional molecular signatures in the viral RNAs and in the proteins they encode, together with data from phylogenetic analyses, support the proposal of creating a new species in the genus Emaravirus to classify the novel virus, which is tentatively named Actinidia chlorotic ringspot-associated virus (AcCRaV). Bioassays showed that AcCRaV is mechanically transmissible to Nicotiana benthamiana plants which, in turn, may develop chlorotic spots and ringspots. Field surveys disclosed the presence of AcCRaV in four different species of kiwifruit vines in five different provinces of central and western China, and support the association of the novel virus with symptoms of leaf chlorotic ringspots in Actinidia. Data on the molecular features of small RNAs of 21-24 nucleotides, derived from AcCRaV RNAs targeted by host RNA silencing mechanisms, are also reported, and possible molecular pathways involved in their biogenesis are discussed.

A new wet reference target method for continuous infrared thermography of vegetations

Although infrared thermography for stress detection in plants is popular in scientific research, it is rarely used in continuous and automated applications. One of the main reasons for this is that the most precise method for generating wet reference targets, used for normalizing the leaf or canopy surface temperature for microclimatic conditions, requires manual wetting before each image capture. In this article, we present and evaluate a new type of wet reference target that remains wet while having an energy balance as similar as possible to that of the canopy. This reference target consists of a cloth knitted around a solid frame whose shape and dimensions mimic those of the leaves. The cloth remains wet by constantly absorbing water from a reservoir.The new reference target was evaluated on grapevine and kiwifruit plants in greenhouse and orchard conditions. In greenhouse conditions, measured stomatal conductance was consistently more highly correlated with the stomatal conductance index Ig when Ig was calculated with the new wet reference rather than the manually wetted reference target. Furthermore, the temperature difference between leaves and the new reference target remained stable for as long as measured, in contrast with the manually wetted leaves. Ig obtained with the new reference target method was also highly correlated with stomatal conductance (gs) of both crops in orchard conditions.A new empirical regression model to estimate gs from Ig in greenhouse conditions was introduced and evaluated. This regression model incorporates the background temperature, a parameter that needs to be included in thermographic measurements for obtaining correct surface temperatures, thus avoiding the need for any additional measurements. The same regression model can be applied on different days with differing conditions. The model performed better than other tested empirical models and provided unbiased estimates of gs on days with different conditions, resulting in a root mean square error of 22–25% of gs. Thus, it provides a promising method for continuous remote sensing of stomatal conductance or drought stress detection of plants and vegetations.

The Influence of Effective Microorganisms on Microbes and Nutrients in Kiwifruit Planting Soil

To understand the effects of effective microorganisms (EMs) containing multiple strains on microbes and nutrients in kiwifruit planting soil, EMs prepared with four different strains were added to kiwifruit planting soil monthly from April to August. The counts of bacteria, fungi, actinomycetes, and total microbes were determined. The pH, total nitrogen (TN), alkali-hydrolyzable nitrogen (A-N), organic matter (OM), available potassium (A-K), and available phosphorus (A-P) of the soil were measured. Results indicated that the counts of bacteria, fungi, actinomycetes, and total microbes reached 60.33 × 105, 4.00 × 105, 0.92 × 105, and 65.25 × 105 CFU/g, respectively, in August, all of which were higher than those of the control group (CK). The bacterial count of the experimental group (EG) was higher than that of the CK in August. The pH-values of the EG were always lower than those of the CK. In August, the TN content of the EG was 1.52 g/kg, which was higher than that of the CK (1.35 g/kg). A significant negative association between the actinomycetes count and TN (p < 0.05) was found. For A-N and OM, the content of the EG (A-N, 125.18 mg/kg; OM, 49.84 mg/kg) was roughly the same as that of the CK (A-N, 112.51 mg/kg; OM, 53.11 mg/kg) in August. However, the A-K and A-P contents of the EG (A-K, 145.25 mg/kg; A-P, 111.25 mg/kg) were lower than those of the CK (A-K, 182.52 mg/kg; A-P, 202.19 mg/kg) in August. Results show that application of EMs in kiwifruit planting soil can increase the counts of soil microbes and might promote the absorption of major nutrients for kiwifruit tree.

Draft Genome Sequences of 18 Strains of Pseudomonas Isolated from Kiwifruit Plants in New Zealand and Overseas.

In this paper, we present the draft sequences of 18 genetically diverse Pseudomonas strains isolated from kiwifruit plants in New Zealand and overseas, including a number that are currently not fully characterized. These sequences will aid in the diagnosis of Pseudomonas on kiwifruit for future pest management and border security decision-making.

Pseudomonas syringae pv. Actinidiae isolated from non-kiwifruit plant species in China

Kiwifruit bacterial canker (KBC), incited by Pseudomonas syringae pv. actinidiae (Psa), may cause severe economic losses to kiwifruit (Actinidia deliciosa and A. chinensis). Many studies have been conducted to clarify relationships between this pathogen and Actinidia species. Conversely, little is known about the chance to colonize alternate hosts and the implications of this possibility on disease spread. In this study, 11 bacterial isolates have been isolated from three wild plant species, Setaria viridis (L.) Beauv., Alternanthera philoxeroides (Mart.) Griseb. and Paulownia tomentosa (Thunb.) Steud., found under or nearby kiwifruit plants affected by bacterial canker. All were identified as Psa based on biochemical tests, specific end-point PCR assays, sequence analysis of single effector genes and MLST. The strains tested positive for pathogenicity, both on wild hosts and on kiwifruit plants. To our knowledge, this is the first report on Psa isolated from non-kiwifruit plants. The proof that Psa can migrate to non-kiwifruit plants raises new issues about the means by which the disease can spread at local and international scales, and the measures to be taken to prevent and control effectively KBC disease.