SUMMARY Pseudomonas syringae pv. actinidiae is the causal agent of bacterial canker of green-fleshed kiwifruit (Actinidia deliciosa) and yellow-fleshed kiwifruit (A. chinensis). A recent, sudden, re-emerging wave of this disease has occurred, almost contemporaneously, in all of the main areas of kiwifruit production in the world,suggesting that it can be considered as a pandemic disease. Recent in-depth genetic studies performed on P. syringae pv. actinidiaestrains have revealed that this pathovar is composed of four genetically different populations which, to different extents, can infect crops of the genus Actinidia worldwide. Genome comparisons of these strains have revealed that this pathovar can gain and lose the phaseolotoxin gene cluster, as well as mobile genetic elements, such as plasmids and putative prophages, and that it can modify the repertoire of the effector gene arrays. In addition, the strains currently causing worldwide severe economic losses display an extensive set of genes related to the ecological fitness of the bacterium in planta, such as copper and antibiotic resistance genes, multiple siderophore genes and genes involved in the degradation of lignin derivatives and other phenolics.This pathogen can therefore easily colonize hosts throughout the year. Taxonomy: Bacteria; Proteobacteria, gamma subdivision; Order Pseudomonadales; Family Pseudomonadaceae; Genus Pseudomonas; Pseudomonas syringae species complex, genomospecies 8; Pathovar actinidiae.

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Pseudomonas syringae pv. actinidiae: a re‐emerging, multi‐faceted, pandemic pathogen

The introduction of Pseudomonas syringae pv actinidiae (Psa) severely damaged the New Zealand kiwifruit industry, which in 2010 was based on only two cultivars Despite an extraordinarily quick and strong response by industry, government, and scientists to minimize the economic and social impacts, the economic consequences of this outbreak were severe Although our understanding of Psa epidemiology and control methods increased substantively over the past six years, the kiwifruit industry largely recovered because of the introduction of a less-susceptible yellow-fleshed cultivar The New Zealand population of Psa is clonal but has evolved rapidly since its introduction by exchanging mobile genetic elements, including integrative conjugative elements (ICEs), with the local bacterial populations In some cases, this has led to copper resistance It is currently believed that the center of origin of the pathogen is Japan or Korea, but biovar 3, which is responsible for the global outbreak, originated in China

The Scientific, Economic, and Social Impacts of the New Zealand Outbreak of Bacterial Canker of Kiwifruit (Pseudomonas syringae pv. actinidiae).

At first glance, the compatibility of social theory and resilience thinking is not entirely evident, in part because the ontology of the former is rooted in social interactions among human beings rather than ecological process. Despite this difference, resilience thinking engages with particular aspects of social organization that have generated intense debates within social science, namely the role of humans as integral elements of social-ecological systems and the processes through which given social structures (including material relations) are either maintained or transformed. Among social theoretical approaches, Actor-Network Theory (ANT) is noted for its distinctive approach to these aspects. ANT proposes that human and nonhuman components (both referred to as actants) have the same capacity to influence the development of social-ecological systems (represented as actor-networks) by enacting relations and enrolling other actors. We explore the notion of agency that is employed in resilience thinking and ANT in order to extend our understandings of human-environment relationships through complementary insights from each approach. The discussion is illustrated by reference to ongoing assessment of resilience as it is experienced and expressed in two distinctive agricultural production systems: Indonesian rice and New Zealand kiwifruit. We conclude by establishing the potential for ANT to provide more profound theoretical conceptualizations of agency, both human and nonhuman, in analyses of social ecological systems.

/pdf/exploring-agency-beyond-humans-the-compatibility-of-actor-1xsbwa52qg.pdf

Exploring agency beyond humans: the compatibility of Actor-Network Theory (ANT) and resilience thinking

Horizontal gene transfer can precipitate rapid evolutionary change. In 2010 the global pandemic of kiwifruit canker disease caused by Pseudomonas syringae pv. actinidiae (Psa) reached New Zealand. At the time of introduction, the single clone responsible for the outbreak was sensitive to copper, however, analysis of a sample of isolates taken in 2015 and 2016 showed that a quarter were copper resistant. Genome sequences of seven strains showed that copper resistance - comprising czc/cusABC and copABCD systems - along with resistance to arsenic and cadmium, was acquired via uptake of integrative conjugative elements (ICEs), but also plasmids. Comparative analysis showed ICEs to have a mosaic structure, with one being a tripartite arrangement of two different ICEs and a plasmid that were isolated in 1921 (USA), 1968 (NZ) and 1988 (Japan), from P. syringae pathogens of millet, wheat and kiwifruit respectively. Two of the Psa ICEs were nearly identical to two ICEs isolated from kiwifruit leaf colonists prior to the introduction of Psa into NZ. Additionally, we show ICE transfer in vitro and in planta, analyze fitness consequences of ICE carriage, capture the de novo formation of novel recombinant ICEs, and explore ICE host-range.

/pdf/evolution-of-copper-resistance-in-the-kiwifruit-pathogen-erhxhtihm5.pdf

Evolution of copper resistance in the kiwifruit pathogen Pseudomonas syringae pv. actinidiae through acquisition of integrative conjugative elements and plasmids

Since 2008, the kiwifruit industry has been devastated by a pandemic outbreak of Pseudomonas syringae pv. actinidiae (Psa), the causal agent of bacterial canker. This disease has become the most significant limiting factor in kiwifruit production. Psa colonizes different organs of the host plant, causing a specific symptomatology on each of them. In addition, the systemic invasion of the plant may quickly lead to plant death. Despite the massive risk that this disease poses to the kiwifruit industry, studies focusing on Psa ecology have been sporadic, and a comprehensive description of the disease epidemiology is still missing. Optimal environmental conditions for infection, dispersal and survival in the environment, or the mechanisms of penetration and colonization of host tissues have not been fully elucidated yet. The present work aims to provide a synthesis of the current knowledge, and a deeper understanding of the epidemiology of kiwifruit bacterial canker based on new experimental data. The pathogen may survive in the environment or overwinter in dormant tissues and be dispersed by wind or rain. Psa was observed in association with several plant structures (stomata, trichomes, lenticels) and wounds, which could represent entry points for apoplast infection. Environmental conditions also affect the bacterial colonization, with lower optimum values of temperature and humidity for epiphytic than for endophytic growth, and disease incidence requiring a combination of mild temperature and leaf wetness. By providing information on Psa ecology, these data sets may contribute to plan efficient control strategies for kiwifruit bacterial canker.

/pdf/pseudomonas-syringae-pv-actinidiae-ecology-infection-4krdx9op6u.pdf

Pseudomonas syringae pv. actinidiae: Ecology, Infection Dynamics and Disease Epidemiology

Presence of Pseudomonas syringae pv. actinidiae (Psa), the causal agent of bacterial canker of kiwifruit, in pollen samples collected from infected and non infected orchards in Italy and in New Zealand was determined by polymerase chain reaction (PCR) and by direct bacterial isolation. Psa was isolated only from pollen samples collected in Italy, including pollen collected from two uninfected orchards, which the following year showed signs of infection. Psa was also detected in pollen collected from male and female vines in an Italian infected orchard. Pollen samples from Italy, but not from New Zealand, were collected with a vacuum device. Psa could not be isolated from any of the 25 New Zealand pollen samples analysed. This is the first report of Psa being associated with pollen. There is currently no evidence that artificial pollination leads to increased infection or that pollen has been responsible for the introduction of Psa in a previously Psa-free area.

/pdf/detection-of-pseudomonas-syringae-pv-actinidiae-in-kiwifruit-4lcxgr2vip.pdf

Detection of Pseudomonas syringae pv. actinidiae in kiwifruit pollen samples.

Pseudomonas syringae pv. actinidiae colonization of kiwifruit flowers and methods to prevent infection

Recent Advances in the Characterisation and Control of Pseudomonas Syringae Pv. Actinidiae, the Causal Agent of Bacterial Canker on Kiwifruit

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Detection of Pseudomonas syringae pv. actinidiae in kiwifruit pollen samples.

Pseudomonas syringae pv. actinidiae colonization of kiwifruit flowers and methods to prevent infection

Recent Advances in the Characterisation and Control of Pseudomonas Syringae Pv. Actinidiae, the Causal Agent of Bacterial Canker on Kiwifruit