Kiwifruit Production Research Articles

Effects of biosolid application on soil properties and kiwi fruit nutrient composition on high-pH soil

Macro- and micronutrient availability in high-pH soil is a major constraint in crop production especially for the sensitive plants, such as kiwi fruit. A field study was conducted to investigate the multiyear effects of biosolid application on nutrient availability of agricultural soil and elemental sufficiency in kiwi fruit. Solar-dried biosolid applied at 0, 25, 50, 100 and 200 t ha−1 annually for successive 2 years. The considered soil properties included pH, EC, organic matter, N, P, K, macro–microelements, heavy metals and DTPA-extractable elements were determined. Results showed that biosolid addition significantly reduced to initial soil pH from 8.2 to 7.8 at higher application doses. Optimization of pH resulted in increased levels of soluble elements in all treatments studied. Biosolid application particularly increased Fe, Cu, Zn, Mn and B concentrations to sufficient levels. Among the other elements analyzed, were not significantly affected by biosolid application. Biosolid addition also increased soil DTPA-extractable elements, especially Cd, Cu, Mn, Pb and Zn. Significant increases in DTPA-extractable elements occurred for increasing application rates at 50, 100 and 200 t ha−1 compared to control. We conclude that municipal biosolid applied at an annual rate at or less than 200 t ha−1 can be safely used for kiwi fruit production on high-pH soils.

A Review of Production and Processing of Kiwifruit

Kiwifruit is native to Asia and has become popular worldwide due to its sensory and nutritional properties. It contains high levels of bioactive compounds such as vitamin C vitamin E, flavonoids, carotenoids and minerals. Kiwifruits show a wide diversity in size, shape, fuzziness, flesh and peel color and flavor. The export of fresh kiwifruit has led to rapid expansion of kiwifruit industry through out the world. kiwifruit has become a commonly consumed fruit and is easily available round the year. Kiwifruit is largely consumed as fresh but it is also available in processed forms as juices, fortified drinks, candies, dehydrated and lyophilized products. Kiwifruit is also minimally processed to provide consumers with ready to eat products. Different preservation techniques have been used so far to preserve minimally processed kiwifruit. Here we are going to review some of these techniques.

Effects of alternatives to hydrogen cyanamide on commercial ‘Hayward’ kiwifruit production

The restriction of Hydrogen Cyanamide (HC) for dormancy interruption of kiwifruit in the European Union leads to a concern among many New Zealand growers, who wonder how long will HC be available in their market. A completely randomized block trial in the Auckland region (New Zealand) compares the performance of two available alternative dormancy breaking treatments - Erger® (ER) and Armobreak® (AB) - with HC - HiCane® - and with the untreated control on green kiwifruit (Actinida deliciosa var. deliciosa ‘Hayward’). After a winter chill period of 1653 Richardson Chill Units, ER advanced significantly bud-break, whereas HC induced a delay. ER also advanced flowering, whereas HC and AB induced a delay. ER however showed the most spread bud-break and flowering. AB and ER induced a significantly lower percentage of winter buds (WB) to break than HC, performing however significantly better than the control. ER and AB grew significantly more inflorescences per winter bud (Kfl/WB), than HC and the control. AB and ER induced less lateral flowers than the control, however more than HC. The higher amount of inflorescences and laterals may lead to a higher need of thinning of these vines, and the possibility of not achieving such high yields or large fruit sizes as using HC. These alternatives induced significantly higher levels of fruit quality parameters such as SSC (soluble solid content) and DM (dry matter), possibly as a result of the modification of the date of bud-break and flowering.

D-PSA-K: A Model for Estimating the Accumulated Potential Damage on Kiwifruit Canes Caused by Bacterial Canker during the Growing and Overwintering Seasons.

We developed a model, termed D-PSA-K, to estimate the accumulated potential damage on kiwifruit canes caused by bacterial canker during the growing and overwintering seasons. The model consisted of three parts including estimation of the amount of necrotic lesion in a non-frozen environment, the rate of necrosis increase in a freezing environment during the overwintering season, and the amount of necrotic lesion on kiwifruit canes caused by bacterial canker during the overwintering and growing seasons. We evaluated the model’s accuracy by comparing the observed maximum disease incidence on kiwifruit canes against the damage estimated using weather and disease data collected at Wando during 1994–1997 and at Seogwipo during 2014–2015. For the Hayward cultivar, D-PSA-K estimated the accumulated damage as approximately nine times the observed maximum disease incidence. For the Hort16A cultivar, the accumulated damage estimated by D-PSA-K was high when the observed disease incidence was high. D-PSA-K could assist kiwifruit growers in selecting optimal sites for kiwifruit cultivation and establishing improved production plans by predicting the loss in kiwifruit production due to bacterial canker, using past weather or future climate change data.

Integration of life cycle assessment and Cobb-Douglas modeling for the environmental assessment of kiwifruit in Iran

This paper aimed at evaluating the environmental impacts of kiwifruit production in Guilan province of Iran using Life Cycle Assessment (LCA) methodology and Cobb-Douglas (CD) modeling. For this purpose, a functional unit (FU) equal to one tonne kiwifruit was applied based on ISO 14,040 methods. Data were obtained from 84 kiwifruit producers using a questionnaire during 2012–2013. Seven impact categories were selected to be evaluated using the life cycle of kiwifruit in the region. The results of data analysis revealed that the amounts of emissions, including NH3, N2O, NOx, CO2, CH4 and SO2, for one tonne production of kiwifruit were 2.00, 0.34, 0.30, 45.08, 0.06 and 0.15, respectively. Characterization indices included global warming potential, acidification, terrestrial eutrophication, land use, the depletion of fossil resources, the depletion of phosphate, and the depletion of potash were calculated as 152.18 kg CO2eq, 3.53 kg SO2eq, 9.15 kg NOxeq, 0.32 ha, 531.23 MJ, 2.57 kg P2O5 and 0.83 kg K2O, respectively. Indicators for environmental index (Eco-indeX) and resource depletion (RDI) were 0.35 and 0.45, respectively. High potentials for environmental impacts due to depletion of phosphate resources and eutrophication in the RDI and Eco-indeX Indicators were found. The results of LCA + CD showed that the impacts of inputs, including diesel fuel, phosphate and potash fertilizers on the yield of kiwifruit were positive, while the impacts of urea fertilizer on the yield was negative. To conclude, due to the high environmental impacts of urea fertilizer and its negative effect on kiwifruit yield, it is recommended to replace urea with other sources of nitrogen fertilizer which have lower environmental impacts.

New Zealand kiwifruit growers’ vulnerability to climate and other stressors

Commercial cultivation of kiwifruit in New Zealand is concentrated in a relatively small area of the North Island. Cultivation is economically significant and growing quickly. However, current understanding of vulnerability for this, and other primary sector activities in New Zealand, makes almost exclusive use of linear outcome-oriented frameworks. Drawing on in-depth, semi-structured interviews with kiwifruit growers and orchard managers, workshops and analysis of secondary data, a “bottom-up” contextual assessment of vulnerability was developed and empirically applied. The findings suggest that climate and markets are the main sources of exposure for growers, with sensitivity moderated by location. Growers employ mostly short-term, reactive adaptive strategies to manage climate exposure and sensitivity, but have less capacity to respond to market-related stressors. Warmer and drier conditions are likely to have adverse effects for kiwifruit production and compound existing vulnerabilities. An ageing population and other processes of rural change may also constrain future adaptation. In order to realise opportunities and minimise losses, longer-term strategic responses are required. The paper demonstrates the need to move beyond outcome-oriented and model-based vulnerability assessments in New Zealand, to consider the broad range of the factors that contribute to vulnerability in the nation’s agricultural sectors. It provides a basis for further consideration of multiple exogenous impacts in the industry and confirms the critical importance of qualitatively vulnerability assessments to determine spatially specific outcomes.

Modeling energy consumption and greenhouse gas emissions for kiwifruit production using artificial neural networks

The purpose of this study was to apply artificial neural networks (ANNs) for forecasting and sensitivity analysis of energy inputs and GHG emissions of three groups of kiwifruit orchards of different sizes in Guilan Province, Iran. The initial data were collected from 80 kiwifruit producers in Langroud City, Guilan Province. The total energy input and output were estimated at 37.32 GJ ha−1 and 43.44 GJ ha−1, respectively. The ANOVA (analysis of variance) results showed significant variance among the different orchard sizes from an energy input point of view. The results revealed that the highest share of energy input was that of nitrogen fertilizer use in kiwifruit production. The main reason for the overuse of nitrogen fertilizer is government subsidies provided for chemical fertilizers, followed by high levels of nitrogen leaching due to high rainfall. The average values of some energy indices, such as energy use efficiency, energy productivity, net energy and energy intensiveness, were calculated as 1.16, 0.61 × 10−3 kg GJ−1, 6.12 GJ ha−1 and 3.27 × 10−3 GJ $−1, respectively. The average total GHG emissions were calculated as 1310 kg CO2eq. ha−1. Nitrogen fertilizer had the highest share in GHG emissions for kiwifruit production, with 26.17% of total emissions. The 12-9-9-2 structure ANN model was the best topology for predicting yield and GHG (greenhouse gas) emissions of kiwifruit production in the studied area. The coefficients of determination (R2) of the best topology calculated were 0.987 and 0.992 for yield and greenhouse gas emissions, respectively, indicating the high correlation in the model. The results of model sensitivity analysis indicated that diesel fuel and nitrogen fertilizer were the most sensitive inputs for kiwifruit yield and greenhouse gas emissions, reflecting the important role of nitrogen fertilizer in the excess energy consumption and greenhouse gas emissions of kiwifruit orchards. According to the current study, it is suggested for new policies to be adopted to reduce nitrogen fertilizer consumption.

Eco-efficiency of organic and integrated kiwifruit production

Eco-efficiency of organic and integrated kiwifruit production

Chitosan coating of red kiwifruit (Actinidia melanandra) for extending of the shelf life

Commercial production of red kiwifruit (Actinidia melanandra) has been unsuccessful because of its short shelf life. Here in this study, we used chitosan to extend the shelf life of red kiwifruit berries. Chitosan (with 70–75% deacetylation degree and low molecular weight) was dissolved in acetic acid (at pH 2.0–2.3) to obtain gel material, which was used for coating of the fruit. The coated and uncoated samples were kept for 26 days at room temperature (20±2°C). The changes in the weight loss, firmness, soluble solid content, total polyphenol content and ascorbic acid content were evaluated. All these findings showed that chitosan could be an effective coating material for berries of red kiwifruit to extend its short shelf life.

Opportunities for environmental modification to controlPseudomonas syringaepv.actinidiaein kiwifruit

Bacterial canker of kiwifruit (Pseudomonas syringae pv. actinidiae; Psa) was first identified in New Zealand kiwifruit orchards in 2010. The bacterial disease has impacted significantly on orchard productivity. 'Hort16A' (Actinidia chinensis), one of the main cultivars in production in 2010, proved susceptible to the disease with large areas now removed. A new Actinidia chinensis cultivar ('Gold3'), with improved tolerance to Psa, has now been released. The kiwifruit industry has made considerable advances in understanding Psa, and extensive research efforts have focussed on control options, including cultivar selection, agrichemical treatments and changes in vine management practices. It is recognised that continued productivity of kiwifruit orchards will involve the adoption of a suite of Psa disease-mitigating practices. Modification of environmental conditions is being explored through the construction of large plastic canopies over orchards. Moisture is required for Psa multiplication and vine infection; the plastic canopies minimise leaf moisture and prevent rainfall from spreading bacteria within the canopy. Additional benefits include protection from wind and frost, environmental conditions that can result in physical damage to the vines, predisposing them to infection. Within a year of the first canopies being constructed, approximately 30 ha of the 'Gold3' has been covered. Research trials have indicated that the canopies reduce the progression of Psa symptoms when covers are constructed over vines with low levels of infection. As the area of kiwifruit production under plastic canopies continues to increase, effects on minimising the impacts of Psa continue to be monitored, and impacts on vine physiology, fruit production and occurrence of other pests and diseases are being explored.

Greenhouse gas emissions footprint of agricultural production in Guilan province of Iran

Agricultural production systems have been contributed to some negative effects on the environment. Therefore, in this research the greenhouse gas (GHG) emissions footprint associated with tea, peanut and kiwifruit production in Guilan province of Iran was studied. Data were collected using farmers’ questionnaire in the 2012–2013 production years. The results revealed that the highest share of GHG emissions for tea, peanut and kiwifruit production systems belonged to chemical fertilizer (76%), diesel fuel (58%) and electricity (47%), respectively. The total GHG emissions footprints for the production of these crops were calculated as 1281.82, 822.29 and 4518.99kgCO2eqha−1, respectively. The correlation between farm size and GHG emissions in the production of all three crops were inverse. It means that the large farms produced the least amount of GHG emissions compared to the small farms in Guilan province of Iran. The amount of GHG emissions footprints per capita of farmers in tea, peanut and kiwifruit production in Guilan province were obtained 256.36, 657.83 and 3163.29kgCO2eq per farmer, respectively. Overall, the amount of GHG emissions per capita of farmers in Guilan province of Iran was 1359.16kgCO2eq in that year.

KIWIFRUIT RESEARCH AND PRODUCTION IN TURKEY

Total world kiwifruit production outside China is currently 1,412,455 t, the total planted area is 98,656 ha, and the production area is increasing each year (FAO, 2012). Cultivation of kiwifruit started in Europe in the 1960s. Towards the end of last century, kiwifruit were introduced to Turkey by the AtatA¼rk Central Horticultural Research Institute in Yalova. Since then, each year has seen increasing interest. Today, Turkey, in terms of kiwifruit plantings, is amongst the more important producers. But productivity is low as most orchards in Turkey are still young; total yields will increase rapidly in the next few years. Commercial orchards are generally A. deliciosa ‘Hayward’ and cultivation of other species or cultivars is very limited. Especially in the northern part of Turkey, climatic conditions are suitable for kiwifruit. The two most common support systems are the T-bar and the pergola and these are used, with some modifications. Psa (Pseudomonas syringae pv. actinidiae) is so far not a serious problem in Turkey but root rots and water-logging problems in heavy soils are very common, so ridge planting is widely used. Frost protection in the form of fogging is also beginning to be used at higher altitudes. In contrast to New Zealand, irrigation of kiwifruit in Turkey is essential and is commonly done by mini-sprinkler systems in the Marmara and the Central Black Sea Regions. In the past, there was little irrigation of orchards in the Eastern Black Sea Region, but more recently irrigation systems have been installed. Consumption of fresh kiwifruit is likely to increase as the Turkish kiwifruit industry develops. Kiwifruit producers in Turkey are organized into small producer associations. However, these have not yet combined to form a national association. Such a combined national organization would make it much easier to solve problems of production, storage, packaging and marketing of Turkish kiwifruit. Kiwifruit research in Turkey first began in the 1990s at the Yalova AtatA¼rk Horticultural Central Research Institute. The number of kiwifruit-related research programmes is increasing each year. The studies so far have concentrated on rooting of cuttings, climate change-adaptation, packaging, cold storage and fruit quality issues.

PEDOCLIMATIC WEB MONITORING SYSTEM FOR PSEUDOMONAS SYRINGAE PV. ACTINIDIAE (PSA) AND ORCHARD MANAGEMENT

The collection of soil and climate data from kiwifruit orchards can constitute a reference for the proper management of kiwifruit cultivation, in particular for control of Pseudomonas syringae pv. actinidiae (Psa), plant nutrition and irrigation. The optimization of irrigation, fertilization, and copper treatment resulted in sustainable production of kiwifruit at reduced costs. The climate monitoring system can also be applied in field trials to study diseases epidemiology and orchard management.

KIWIFRUIT BREEDING AND OBTAINING NEW CULTIVARS IN TURKEY

Kiwifruit have been grown in Turkey for 25 years, especially in the Marmara and Black Sea regions. Mainly it is the Actinidia deliciosa cultivar ‘Hayward’ that is grown. However, in recent years, different cultivars and species have started to be grown as their fruit fetch higher prices in the market. As world production of kiwifruit has increased, so prices have declined. Increased product diversity, in the Actinidia species and cultivars grown, and improvements in fruit quality should help to prevent such a decline in prices. For this reason, the Yalova AtatA¼rk Central Horticultural Research Institute has initiated a kiwi breeding program in order to obtain new kiwifruit cultivars with superior characteristics. In this breeding program A. chinensis Jintao® (J), A. chinensis ‘Hort16A’ (HO), A. chinensis cultivar B (B) seedlings and A. deliciosa ‘Hayward’/Top Star® A— ‘Tomuri’ (TH) hybrids have been studied. Some phenological and pomological evaluations of these hybrids were conducted for three years. Priority has been given to selections with yellow fruit flesh and hairless skins for the evaluation of flavour and aroma. Very recently, some promising candidates have been selected to become the new kiwifruit cultivars of Turkey. Cultivation of these new cultivars should increase the profitability of orchards. This should allow the greatly expanded expected production in the near future, ten times more than at present, to be profitable.

UNDERSTANDING POSTHARVEST QUALITY OF KIWIFRUIT IN RELATION TO SHOOT AND CANE VIGOR

Global kiwifruit production has expanded considerably. Over-softening and a low soluble solids concentration of kiwifruit after storage are the main factors associated with market satisfaction. Variability between kiwifruit batches, which is associated with season, orchard, pre- and postharvest practices, can result in fruit with unpredictable postharvest quality. The origin of fruit from different locations on a vine was used to explain the variation at harvest and postharvest quality. Fruit selected from different associations between shoot and cane vigor (evaluated by diameter) from vines of three orchards with demonstrated that fruit growing on terminated shoots was dominant. In addition, dry matter concentration and ripe soluble solids concentration were not affected by cane or shoot diameter. Further, fruit size was positively related to terminated shoot length and firmer fruit developed on non-terminated shoots compared with terminated shoots when assessed after ripening. These data were validated during the following year using data collected from eight orchards. Here, a comparison of fruit from non-terminated shoots with a small diameter (8.1-9.6 mm) growing on medium-diameter canes (22.4-24.5 mm) and from terminated shoots with a medium diameter (10.7-11.7 mm) growing on small-diameter canes (15.2-15.9 mm) demonstrated that terminated shoots produced softer fruit, and the nitrogen concentration in the pulp of these kiwifruits at harvest was negatively correlated with fruit firmness measured after 75 days at 0°C + 4 days at 20°C.

TRANSPOSITION, INSERTION, DELETION AND RECOMBINATION DRIVE VARIABILITY IN THE TYPE 3 SECRETOME OF PSEUDOMONAS SYRINGAE PV. ACTINIDIAE, THE TRANSITION FROM GLOBAL EFFECTOR COMPARISONS TO KIWIFRUIT RESISTANCE BREEDING STRATEGIES

A strain of Pseudomonas syringae pv. actinidiae (Psa) that is particularly virulent (Psa-V or biovar 3) is responsible for the recent devastating global outbreak of bacterial canker on kiwifruit vines. We have now sequenced the genomes of over 30 isolates of Psa from around the world including two genomes (Psa-V and the type strain) to near completion. This extensive resource of genomic information has allowed us to reveal the remarkable plasticity exhibited by this pathogen and trace its evolution from the first geographically limited outbreaks on commercial kiwifruit production in the 1980s to the present global outbreak. We present examples of how this plasticity is driven by several different mechanisms including transposition, insertions/deletions and genome level recombination events and has resulted in at least four major phylogenetically defined groupings of Psa strains. These mechanisms have scrambled long distance co-linearity between even the most closely related of these phylogenetic groups, underlining the pace of genome-wide evolution in P. syringae pathovars. We focus on the impact of these events on the effector complement of the four main groupings of Psa strains in particular. As the loss of host resistance is typically linked with loss of these effectors we discuss how this knowledge is now being used to inform the long-term resistance breeding strategies being developed against this very damaging pathogen.

UNRAVELING THE MOLECULAR INTERACTION BETWEEN PSEUDOMONAS SYRINGAE PV. ACTINIDIAE (PSA) AND THE KIWIFRUIT PLANT THROUGH RNASEQ APPROACH

Bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa), is the most important disease of kiwifruit, threatening kiwifruit production around the world. However, little is known about the molecular interaction between Psa and kiwifruit plants. To elucidate early molecular plant response during the different phases of the infection, gene expression in healthy or inoculated plants of Actinidia chinensis was analyzed 3, 24 and 48 h after experimental inoculation. In addition, to understand the molecular mechanism underlying the increased plant resistance observed after the exogenous application of the systemic acquired resistance (SAR) inducer acibenzolar- S-methyl (ASM), gene expression was analyzed in healthy or inoculated ASM pre-treated plants. Transcriptome analysis of A. chinensis, was performed using an Illumina GAIIx sequencer, generating 221 million 75 bp long paired end reads. The raw reads were de novo assembled into 63,943 contigs by Trinity software with an average size of 1,078 bp and N50 of 1,614 bp. Annotation of the de novo transcript contigs was done using Blast2GO software, BLASTX was performed against the NCBI non-redundant protein database with an E-value cut-off of 1e-5. Mapped records were also aligned to protein databases such as Swiss-Prot, KEGG and COG, in order to retrieve proteins with the highest sequence similarity, to give a putative functional annotation. Finally, InterProScan was used to identify additional gene ontology (GO) annotations. Reads were mapped to the contigs using the CLC software to identify differentially expressed genes (DEGs), statistical analysis was done using the method described in the R package DESeq. A preliminary analysis of DEGs was conducted on sequences obtained 24 h after infection. A total of 349 DEGs were identified in response to infection in non-ASM pre-treated plants. When ASM pre-treated plants were considered, 637 DEGs were identified, 213 of them were in common with the 349 DEGs modulated by infection in not ASM pre-treated plants. The ASM treatment by itself was able to modulated 974 DEGs, 70 of them were further modulated by infection in ASM pre-treated plants. These results suggest that the molecular response to Psa is strongly enhanced in ASM pre-treated plants.

Study on comparative efficacy of bio-organic nutrients on plant growth, leaf nutrient contents and fruit quality attributes of kiwi fruit

The comparative efficacy of bio-organic nutrients on cropping behavior and fruit quality of kiwifruit was analyzed using farm yard manure (FYM), vermicompost (VC), biofertilizers (BF), green manure (GM), and vermiwash (VW). Among various treatments the combination of FYM at 15 kg/vine, GM, VC at 15kg/vine, BFat50-g/ vine and VW at 2kg/vine significantly improved cropping behavior. This superior combination also resulted in considerably greater amounts of leaf macro-and micronutrients: N (2.49%), P (0.26%), K (1.48%), iron (Fe: 208.0 mg/kg), copper (Cu: 17.8 mg/kg), zinc (Zn: 36.2 mg/kg), and manganese (Mn: 88.3 mg/kg),which might be responsible for better cropping behavior, productivity and nutrient profile for sustainable kiwi fruit production. It can be concluded that with use of various sources of bio-organic materials under organic farming regime, there will be sufficient improvement in fruit quality and plant nutrient contents.

Identification of Botryosphaeriaceae Species Causing Kiwifruit Rot in Sichuan Province, China.

Species of Botryosphaeriaceae fungi are important plant pathogens causing cankers, blight, and fruit rot in an extremely wide range of host. In recent years, kiwifruit rot has been a serious problem in Sichuan Province, one of the important kiwifruit production areas of China. Botryosphaeria dothidea has previously been associated with kiwifruit rot but little is known regarding whether other Botryosphaeriaceae genera also constitute kiwifruit rot pathogens in China. Accordingly, diseased fruit were collected from six different areas of Sichuan Province. Based on morphological characteristics, pathogenicity testing, and comparisons of DNA sequences of the internal transcribed spacer, transcription elongation factor 1-α, and β-tubulin genes, 135 isolates of Botryosphaeriaceae were identified as B. dothidea, Lasiodiplodia theobromae, and Neofusicoccum parvum. All of these species were found to cause kiwifruit rot. To understand the infection cycle of kiwifruit rot pathogens, these three species were used to inoculate leaves and shoots of kiwifruit. The results showed that these species could cause spots on leaves and lesions on shoots, producing abundant pycnidia on leaves and shoots surfaces. Moreover, B. dothidea conidia and ascospores from overwintered pycnidia and pseudothecia in kiwifruit orchards in April and August could cause fruit rot and spots on leaves of kiwifruit. Therefore, we concluded that overwintered pycnidia and pseudothecia of B. dothidea in kiwifruit orchards are the primary inoculum for kiwifruit rot, with new pycnidia that develop during the growing season serving as a secondary inoculum. This is the first report of N. parvum and L. theobromae causing kiwifruit rot in China and is also the first report that B. dothidea is able to overwinter as pycnidia and pseudothecia in kiwifruit orchards and serve as the primary inoculum for kiwifruit rot.

Bactericidal Compounds Controlling Growth of the Plant Pathogen Pseudomonas syringae pv. actinidiae, Which Forms Biofilms Composed of a Novel Exopolysaccharide.

Pseudomonas syringae pv. actinidiae is the major cause of bacterial canker and is a severe threat to kiwifruit production worldwide. Many aspects of the disease caused by P. syringae pv. actinidiae, such as the pathogenicity-relevant formation of a biofilm composed of extracellular polymeric substances (EPSs), are still unknown. Here, a highly virulent strain of P. syringae pv. actinidiae, NZ V-13, was studied with respect to biofilm formation and architecture using a flow cell system combined with confocal laser scanning microscopy. The biofilm formed by P. syringae pv. actinidiae NZ V-13 was heterogeneous, consisting of a thin cellular base layer 5 μm thick and microcolonies with irregular structures. The major component of the EPSs produced by P. syringae pv. actinidiae NZ V-13 bacteria was isolated and identified to be an exopolysaccharide. Extensive compositional and structural analysis showed that rhamnose, fucose, and glucose were the major constituents, present at a ratio of 5:1.5:2. Experimental evidence that P. syringae pv. actinidiae NZ V-13 produces two polysaccharides, a branched α-d-rhamnan with side chains of terminal α-d-Fucf and an α-d-1,4-linked glucan, was obtained. The susceptibility of the cells in biofilms to kasugamycin and chlorine dioxide was assessed. About 64 and 73% of P. syringae pv. actinidiae NZ V-13 cells in biofilms were killed when kasugamycin and chlorine dioxide were used at 5 and 10 ppm, respectively. Kasugamycin inhibited the attachment of P. syringae pv. actinidiae NZ V-13 to solid surfaces at concentrations of 80 and 100 ppm. Kasugamycin was bacteriostatic against P. syringae pv. actinidiae NZ V-13 growth in the planktonic mode, with the MIC being 40 to 60 ppm and a bactericidal effect being found at 100 ppm. Here we studied the formation, architecture, and composition of P. syringae pv. actinidiae biofilms as well as used the biofilm as a model to assess the efficacies of bactericidal compounds.