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Since 2008 Psa ( Pseudomonas syringae pv. actinidiae) has become a threat for kiwifruit plantation in many Countries. A lot of research and trials have been carried out looking for chemicals able to stop the infection, acting directly on the agent of the disease. This study is targeted on the “environment” corner of the disease triangle, with the aim of creating an overall environment unfavorable to Psa development, considering the effect of change not only on the disease, but also on growing parameters. The objective is achievable growing kiwifruit under green house in different structures. Zespri in conjunction with the University of Bologna built up three years of growing experience under covers, so the present work wants to underline the outcomes of it. It has been proved that growing kiwifruit under cover reduces significantly the symptoms of Psa. This is likely linked to lower bacteria’s population, both epiphytic and endophytic. Beside the effect on bacteria’s population, effect on fruit quality was observed. Earlier fruit set was recorded under the cover due to the warmer spring temperature. It also resulted in bigger fruit size at harvest with less blemish. In fact, plastic covers protect the crop from adverse climate events, such as wind and hail. Generally, under cover kiwifruit needs a limited number of chemical treatments, with benefit on soil compaction (fewer sprays and in better soil condition – no wet soil). The controlled climate condition allowed to operate with no weather constrains: this was particularly helpful at pollination time, but also in a Psa safer environment for summer pruning, harvest and so forth, where wounds could get infected. In the other hand, growing kiwifruit under plastic cover showed some constrains. Primary, building a structure that can resist to climate events, like wind storms or hail and snow precipitation is generally highly expensive. In addition, the plastic covers last few years (5-6 years), or at least the light permeability decreases dramatically, requiring to replace it. This implies frequent substitution of the plastic sheet, with extra charge of cost to add to the balance. Data have been collected about change in amount and quality of the light. Although in Italy it is not a big issue during sunny days, it may become a problem when it is cloudy, causing a decrease of the photosynthesis: this can impact dry matter accumulation, resulting in lower fruit quality. Care must be paid to irrigation and nutrition management, since salinity can easily build up in the root area, due to the quality of irrigation water and/or the fertilizer application. In fact, the complete absence of precipitation avoids regular wash off/dilution of the salinity, accumulating in narrow layer compressed by the irrigation volume applied. In conclusion, this paper as result of ongoing monitoring, highlights all the side effects of plastic covers, both positive and negative, on kiwifruit crop

A forecasting model to predict the kiwifruit bacterial canker infections was developed in New Zealand. In 2012 such forecasting model was intended to be validated in the kiwifruit growing areas of Emilia-Romagna Region. Model, using hourly temperature and leaf wetness data, calculates the bacteria multiplication rates (M). M values were three days accumulated (actual + two preceding days) to provide a daily Risk Index R whenever a rain event (> 1mm) occur during the growing season. Validation was carried over 2012-2014, exposing micro-propagated potted kiwi plantlets under untreated infected plants from march untill november. Every week, after being exposed, 18 Plantlets (9 Hayward and 9 Tomuri) were removed and placed in climate chamber with 24 hours wetness duration. Afterwards, part of them were placed in greenhouse at 15-18°C temperature to check for symptom occurrence, and the remaining analyzed by both pathogen isolation on selective growing media and PCR on isolated bacterial colony. Analysis were carried out as soon as kiwi plantlets were remove from the field (T0) and after 7 days (T7). In 2012 an 2013, the experiment was carried out in two kiwi orchard of the cv Hayward (1 located in the plain and 1 in the hillside), while in 2014 the experiment was carried out on 2 A.deliciosa and 1 A.chinensis orchards. Over the years 2012-2014, symptoms on plantlets were always observed from march to the first week of june. In the same period of time disease symptoms occurred in the unprayed kiwifruit plot, confirming what observed in potted trap plants. However diagnostic analysis showed that bacteria can be detected in potted trap plants throughout the year (particularly in 2013 and 2014), except some sporadic week during summer even without a rain event. Validation experiment using trap plants permitted to effectively validate the forecasting model during springtime (from march to june) showing a robust correspondence between the infection index R and the symptom occurrence. In fact, all the disease symptoms occurred in coincidence of R infection Index higher than 15, value that can be taken as action threshold. At the same time, molecular analysis as well showed a clear relationship between the infection index R and the bacterial inoculum contaminating the trap plants during the growing season.

Italy has a preeminent rank in kiwifruit industry, being the first exporter and the second largest producer after China. However, in the last years kiwifruit yields and the total cultivated area considerably decreased, due to the pandemic spread of the bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa). Several climatic conditions and cultural practices affect the development of the bacterial canker. This research work focused on the impact of agricultural practices and microclimate conditions on the incidence and epidemiology of Psa in the orchard. Therefore, the effect of fertilization, irrigation, use of bio-regulators, rootstock, training system and pruning were examined. The effect of different tunnel systems was analyzed as well, to study the plant-pathogen interaction. Considering the importance of insects as vectors in other pathosystems, the role of Metcalfa pruinosa in the spread of the bacterial canker was investigated in controlled conditions. In addition, quality and storage properties of fruits from infected plants were assessed. The study of all these aspects of the agronomic practices is useful to define a strategy to limit the bacterial diffusion in the orchard. Overall, excess nitrogen fertilization, water stress, stagnant water supplies, pruning before summer and the high number of Metcalfa pruinosa increased the Psa incidence. In contrast, tunnel covers may be useful for the control of the disease, with special attention to the kind of material.

The bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae, is considered one of the most severe diseases affecting several cultivated Actinidia species, including A. chinensis and A. deliciosa. Kiwifruits have been always considered fruit with an high intrinsic quality due to the strong nutraceutical value, but also to the absence of contaminants such as pesticide residues. With the emergence of this devastating disease, the use of pesticides rapidly increased and therefore the kiwifruit quality can be maintained only by ensuring agricultural practices that reduce the need of toxic xenobiotic compounds. The aim of this study was to provide an in-depth understating of the influence of agricultural practices on disease development and spread and to harmonise the agricultural practices with the current disease control inputs. Therefore, the role of fertilization, irrigation, use of bio-regulators, rootstock, training system and pruning on the incidence and epidemiology of PSA were examined. Nitrogen fertilization had a direct effect on the pathogen's endophytic growth. Furthermore, the depletion of some micronutrients, such as iron, increased the disease. The water stress consequent to a reduced irrigation resulted in higher symptoms. Concerning pruning, the open cuts remains a possible entry point for more than 30 days. In addition, the pruning performed in late season resulted more risk for infection. To test curative pruning, preliminary data were collected on the migration rate of Psa inside the different plant organs. Among the different training system evaluated in this study, the gender double curtain the allowed a more efficient penetration of the phytosanitary treatments that may increase the disease control. However, no differences on disease incidence were observed. Concerning the use of bioregulators, synthetic gibberellin, such as forchlorfenuron, reduced in controlled condition both the disease incidence and severity. Synthetic auxins, on the other hand, showed a detrimental effect with higher symptomatology. In field conditions, none of the used bioregulators showed any effect on the disease incidence and development. Several species were tested for their susceptibility to Psa in order to develop a tolerant rootstock. Arguta spp. resulted the most tolerant to the disease and further experiments are need to test its possible exploitation as a commercial rootstock. Finally, the a preliminary guideline harmonizing the best cultural practices with the most widely used control methods (i.e resistance inducers and copper) is provided.

The micro-climatic conditions inside orchards and the vine canopy are critical factors in determining the local severity and extent of the bacterial canker of kiwifruit ( Pseudomonas syringae pv. actinidiae -Psa). Among these conditions, the effect of light quality and intensity has received, so far, little attention. Light intensity and quality are crucial factor influencing plant development, but they may also affect movement, survival and virulence of Psa. The use of plastic covers is an emerging practice showing some effect in reducing Psa incidence and severity. The effect of plastic tunnel is probably related to both a modification of the microclimatic conditions (i.e. a reduction in leaf weatness) and to an increased permanence of control treatments on the leaves. Our study aimed to evaluate the effect of plastic covers on Psa symptom development and on the micro-climatic conditions in the orchard. In this study the use of permanently closed tunnel and seasonal closed tunnel were tested in two infected commercial A. chinensis orchards. The use of permanently closed tunnel showed a positive result in the control of the disease by the reduction of the leaf wetness. Finally, since commercial plastic tunnel might modify light intensity and composition, trials were performed in laboratory conditions to evaluate the effect of light on the bacterium pathogenicity and plant defenses. Concerning Psa virulence, phenotypes and the expression of genes related to motility, biofilm formation and virulence were considered. To evaluate the influence on plant resistance, callose formation, expression of defense related genes and susceptibility were considered.

Prevenzione ed equilibrata gestione vegeto-produttiva dell'impianto: fattori difficili da determinare con precisione scientifica, ma assai influenti sulla suscettibilità dell'actinidieto alle infezioni da Psa. Va evitato ogni tipo di abuso di mezzi tecnici che possono rendere le piante più performanti, ma allo stesso tempo più deboli.

Stress-induced mitophagy, a tightly regulated process that targets dysfunctional mitochondria for autophagy-dependent degradation, mainly relies on two proteins, PINK1 and Parkin, which genes are mutated in some forms of familiar Parkinson’s Disease (PD). Upon mitochondrial damage, the protein kinase PINK1 accumulates on the organelle surface where it controls the recruitment of the E3-ubiquitin ligase Parkin. On mitochondria, Parkin ubiquitinates a subset of mitochondrial-resident proteins located on the outer mitochondrial membrane, leading to the recruitment of downstream cytosolic autophagic adaptors and subsequent autophagosome formation. Importantly, PINK1/Parkin-independent mitophagy pathways also exist that can be counteracted by specific deubiquitinating enzymes (DUBs). Down-regulation of these specific DUBs can presumably enhance basal mitophagy and be beneficial in models in which the accumulation of defective mitochondria is implicated. Among these DUBs, USP8 is an interesting target because of its role in the endosomal pathway and autophagy and its beneficial effects, when inhibited, in models of neurodegeneration. Based on this, we evaluated autophagy and mitophagy levels when USP8 activity is altered. We used genetic approaches in D. melanogaster to measure autophagy and mitophagy in vivo and complementary in vitro approaches to investigate the molecular pathway that regulates mitophagy via USP8. We found an inverse correlation between basal mitophagy and USP8 levels, in that down-regulation of USP8 correlates with increased Parkin-independent mitophagy. These results suggest the existence of a yet uncharacterized mitophagic pathway that is inhibited by USP8.

Flowers can provide a protected and nutrient-rich environment to the epiphytic microflora, thus representing a sensible entry point for pathogens such as Pseudomonas syringae pv. actinidiae (Psa). This bacterium can colonize both male and female Actinidia flowers, causing flower browning and fall, and systemic invasion of the host plant, eventually leading to its death. However, the process of flower colonization and penetration into the host tissues has not yet been fully elucidated. In addition, the presence of Psa in the pollen from infected flowers, and the role of pollination in the spread of Psa requires confirmation. The present study employed a Psa strain constitutively expressing the fluorescent GFPuv protein, to visualize in vivo flower colonization. Microscopy observations were performed by means of confocal laser scanning and wide-field fluorescent microscopy, and were coupled with the study of Psa population dynamics by quantitative PCR (q-PCR). The pathogen was shown to colonize stigmata, move along the stylar furrow, and penetrate the receptacles via the style or nectarhodes. Once the receptacle was invaded, the pathogen migrated along the flower pedicel and became systemic. Psa was also able to colonize the anthers epiphytically and endophytically. Infected male flowers produced contaminated pollen, which could transmit Psa to healthy plants. Finally, pollinators (Apis mellifera and Bombus terrestris) were studied in natural conditions, showing that, although they can be contaminated with Psa, the pathogen’s transmission via pollinators is contrasted by its short survival in the hive.

After 20 years of steady increase, kiwifruit industry faced a severe arrest due to the pandemic spread of the bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa). The bacterium penetrates the host plant primarily via natural openings or wounds, and its spread is mainly mediated by atmospheric events and cultural activities. Since the role of sucking insects as vectors of bacterial pathogens is widely documented, we investigated the ability of Metcalfa pruinosa Say (1830), one of the most common kiwifruit pests, to transmit Psa to healthy plants in laboratory conditions. Psa could be isolated both from insects feeding over experimentally inoculated plants, and from insects captured in Psa-infected orchards. Furthermore, insects were able to transmit Psa from experimentally inoculated plants to healthy ones. In conclusion, the control of M. pruinosa is recommended in the framework of protection strategies against Psa.

BACKGROUND: The bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae (Psa), affects several cultivated Actinidia species, including A. chinensis and A. deliciosa . Its development is related to permissive environmental conditions, such as temperature, humidity, presence of entry points, genetic and physiological features of the host plant. Moreover, also cultural practices influence, directly or indirectly, the disease development. The bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae (Psa), affects several cultivated Actinidia species, including A. chinensis and A. deliciosa . Its development is related to permissive environmental conditions, such as temperature, humidity, presence of entry points, genetic and physiological features of the host plant. Moreover, also cultural practices influence, directly or indirectly, the disease development. OBJECTIVE: The role of agricultural practices on disease development and spread was studied. The role of agricultural practices on disease development and spread was studied. METHODS: Irrigation, pruning and training systems were tested in the field according to conventional orchard management. Experiments on mineral nutrition, use of bio-regulators and rootstock susceptibility were performed in controlled conditions. Bacterial growth, symptom development and disease incidence were assessed in relation to the different practices. Irrigation, pruning and training systems were tested in the field according to conventional orchard management. Experiments on mineral nutrition, use of bio-regulators and rootstock susceptibility were performed in controlled conditions. Bacterial growth, symptom development and disease incidence were assessed in relation to the different practices. RESULTS: High nitrogen fertilization, iron deficiency and water stress were related to more severe symptoms. Open canopies allow a better irradiation, aeration, and penetration of phytosanitary treatments. Synthetic gibberellins reduced disease incidence and severity in controlled conditions. Fruits from diseased plants showed a lower quality and storability. High nitrogen fertilization, iron deficiency and water stress were related to more severe symptoms. Open canopies allow a better irradiation, aeration, and penetration of phytosanitary treatments. Synthetic gibberellins reduced disease incidence and severity in controlled conditions. Fruits from diseased plants showed a lower quality and storability. CONCLUSIONS: Dense canopies are harder to manage and more exposed to bacterial canker. Pruning tools and irrigation water are relevant for the bacterial spread. Dense canopies are harder to manage and more exposed to bacterial canker. Pruning tools and irrigation water are relevant for the bacterial spread.