Outbreak of Pseudomonas syringae pv. actinidiae in Italy: addition to the EPPO Alert List
Kiwifruit (Actinidia spp.) can suffer from different bacterial diseases: Pseudomonas syringae pv. syringae (bacterial blossom blight), Pseudomonas viridiflava (bacterial leaf blight) and Pseudomonas syringae pv. actinidiae (bacterial canker). Bacterial canker was first observed in Japan in the 1980s. In 1984, strains were isolated in the Shizuoka Prefecture from diseased kiwifruits which were showing cankers on the trunks and main twigs, as well as shoot blight and brown leaf spot lesions surrounded by a chlorotic halo. The causal agent of bacterial canker was identified as a new pathovar of Pseudomonas syringae, and called Pseudomonas syringae pv. actinidiae. In the Republic of Korea, the bacterium was first detected in 1988 in Cheju Island, and it rapidly spread across the production areas of kiwifruit (mainly along the south coast of Korea). In both Korea and Japan, bacterial canker is considered as a limiting factor for the production of kiwifruit with significant losses in the production of fruit and plant mortality.
In the EPPO region, P. syringae pv. actinidiae was detected for the first time in 1992 in Italy (see EPPO RS 93/103). Italy is the major producer of kiwifruit in the world (more than 470 000 tons per year), and is the first exporter together with New Zealand. The main production areas are located in Lazio, Piemonte, Emilia-Romagna, and Veneto (covering at total area of approximately 27 000 ha). In Italy, Actinidia deliciosa cv. ‘Hayward’ is the most widely grown cultivar but since in last 10 years, yellow fleshed cultivars A. chinensis cvs. ‘Hort 16A’ and ‘Jin Tao’ are increasingly being produced. In spring and summer 1992, a new disease causing cankers, red-rusty exudations on twigs, and brown leaf spots was observed in 3 kiwifruit orchards (A. deliciosa cv. ‘Hayward’) in the province of Latina (Lazio region). After this initial record, P. syringae pv. actinidiae was sporadically isolated in the same area but did not cause significant losses. At that time, it was assumed that the disease had been introduced by infected propagation material, because 2-year old plants were mainly affected. But since 2007/2008, the disease has increasingly been observed in Northern Italy (Lazio), and sporadic cases of bacterial canker have been reported from Emilia-Romagna (as of October 2009, the identity of the bacterium has been confirmed on A. chinensis cv. ‘Hort 16A’ in two cases). Surveys were conducted in 2007/2008 in Northern Italy, and showed that P. syringae pv. actinidiae occurred in several orchards in Latina and Rome provinces (Lazio region) and in the province of Treviso (Veneto region). In the orchards, the disease incidence ranged from 50% to 80% and in some cases of high disease incidence, the destruction of the whole orchard was required. The highest disease incidence was associated with A. chinensis cultivars, in particular with the yellow fleshed cultivar ‘Hort 16’ in Latina and Rome provinces, where it reached at least 70% in most cases. In Treviso province, A. chinensis cv. ‘Jin Tao’ showed a lower disease incidence and severity, because symptoms were mainly affecting leaves, buds and flowers. In Italy, it is estimated that the economic losses (including impact on trade) due to P. syringae pv. actinidiae have reached 2 million euros. Because bacterial canker of kiwifruit is spreading in Italy together with an increasing incidence, the EPPO Secretariat decided to add P. syringae pv. actinidiae to the Alert List.
Pseudomonas syringae pv. actinidiae (Bacterial canker of kiwifruit)
Why: Bacterial canker of kiwifruit caused by Pseudomonas syringae pv. actinidiae was first described in Japan in the 1980s causing damage in Actinidia orchards. The disease was then observed in Korea where it also caused economic losses. In the EPPO region, the disease was first noticed in Northern Italy in 1992 where it remained sporadic and with a low incidence during 15 years. But in 2007/2008 economic losses started to be observed particularly in the Lazio region and the possible spread of the disease to other kiwifruit producing regions in Italy began to raise concerns. Because P. syringae pv. actinidiae is currently emerging in the Mediterranean region, the EPPO Secretariat decided to add it to the EPPO Alert List.
Where: Although P. syringae pv. actinidiae was originally described in Japan, its area of origin has not been ascertained. For example, comparison studies between Korean and Japanese strains showed that they have different phylogenic origins.
EPPO region: Italy (Emilia-Romagna, Lazio, Veneto).
Asia: China (Anhui), Japan (Hokkaido (on Actinidia arguta), Honshu, Kyushu, Shikoku), Korea Republic.
Data is lacking on the situation of P. syringae pv. actinidiae in China (where Actinidia species originate from); only a small number of records were reported from the province of Anhui. In the literature, several papers mention the presence of P. syringae pv. actinidiae in Iran, but the original publication only refers to P. syringae pv. syringae.
On which plants: Actinidia species: A. deliciosa, A. chinensis, A. arguta, and A. kolomikta (there is no data on the susceptibility of other Actinidia species). Observations made in Italy suggested that damage is more severe on yellow fleshed kiwifruit (i.e. A. chinensis cvs. ‘Hort 16A’ and ‘Jin Tao’) than on the more widely grown green fleshed cultivar (i.e. A. deliciosa cv. ‘Hayward’).
Damage: P. syringae pv. actinidiae causes brown discolouration of buds, dark brown spots surrounded by yellow haloes on leaves, cankers with reddish exudates on twigs and trunks, fruit collapse, wilting and eventually plant mortality. The most conspicuous symptom is the red-rusty exudation which covers bark tissues on trunks and twigs. Removal of the bark usually reveals a brown discoloration of the external vascular tissues and reddening of the tissues beneath lenticels.
Transmission: Data is lacking on the epidemiology of the disease. It has been observed that the pathogen is active between 10 to 20 °C and is limited by temperatures above 25°C. Inoculation studies showed that the bacterium can infect the plant through natural apertures (stomata, lenticels) and wounds. Symptoms are usually expressed during spring and autumn when climatic conditions are favourable to the disease (cool temperatures, persistent rains, high humidity). It is suspected that the bacterium is spread by heavy rainfalls, strong winds, animals and humans. Over long distances, trade of infected planting material can spread the disease.
Pathway: Plants for planting of Actinidia spp. (infected fruits cannot be totally excluded but seem very unlikely).
Possible risks: Kiwifruits (A. deliciosa and A. sinensis) are economically important crops which are grown in several EPPO countries (by order of importance in production: Italy, Greece, France, Portugal and Spain). In Japan and Korea, bacterial canker has become one of the most serious limiting factors for cultivating kiwifruit. In Italy, it is estimated that the economic losses (including impact on trade) due to P. syringae pv. actinidiae have reached 2 million euros. Control strategies are being developed against the disease and include preventive measures (e.g. good fertilization, avoidance of overhead irrigation, disinfection of pruning equipment, pruning and destruction of diseased parts), regular inspections of the orchards for disease symptoms, and the use of healthy planting material. Chemical control has been implemented in Japan (e.g. with copper compounds and antibiotics), but this has lead to the appearance of resistant strains. It seems desirable to better understand the biology of P. syringae pv. actinidiae in order to develop adequate control strategies in areas where it occurs, and to avoid its further spread in Europe.
EPPO RS 2009/215
Panel review date: -
Entry date 2009-11
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