Kiwifruit Bacterial Canker: the pathogen (PSA) survives on other plant species
During recent years, these issues have been addressed by virtue of extensive international cooperation taking place between the research Team of Prof. Balestra, at the Dip. DAFNE University of Tuscia (I) and of Prof. Zhu, at the Key Lab of Pomology, School of Horticulture, Anhui Agricultural University, Hefei, Anhui provinces, China.
In this study, part of a large epidemiological survey in progress in China, 11 bacterial isolates were isolated by three wild plant species, Setaria viridis (L.) Beauv., Alternanthera philoxeroides (Mart.) Griseb. and Paulownia tomentosa (Thunb.) Steud., found close to Actinidia spp. plants affected by kiwifruit bacterial canker. All isolates based on specific physiological, nutritional, biochemical and genetic tests, were identified as PSA. In addition, all bacterial isolates were positive by pathogenicity tests, both, on wild plant species from which they were isolated and on cultivated Actinidia spp. plants.
The results will be published shortly in the international scientific journal European Journal of Plant Pathology ("Pseudomonas syringae pv. actinidiae isolated from non-kiwifruit plant species in China", Authors: Pu Liu, Xue Shizhou, Rong He, Jiayong Hu, Wang Xiaojie, Bing Jia Lorenzo Gallipoli, Angelo Mazzaglia, Giorgio M. Balestra, Zhu Liwu).
Based on current knowledge, this is the first scientific evidence relating to the isolation of PSA from wild plants. The fact that this bacterium can survive and colonize other plants in addition to those of kiwifruit raises new questions about the strategies adopted by this pathogen to spread both locally, and internationally, such as questions about the measures to be adopted to prevent and effectively control spread of kiwifruit bacterial canker.
This study is the first PSA signaling, not only the survival, but also about the parasitic activities of this pathogen on non-kiwifruit plants. He was discovered by field observations of necrotic spots, similar to those caused by PSA on kiwifruit plants, on the leaves of some wild plants grown close to kiwifruit orchards showing symptoms resembling those caused by PSA.
The isolation from diseased tissues allowed to obtain bacterial colonies with morphological and biochemical characteristics perfectly match with those of Psa. In addition, two PCR tests end-point, the sequence analysis of two effector genes and the analysis of MLST five housekeeping genes, have confirmed not only that the strains isolated from kiwi plants were PSA, but also that they belonged to biovar 3.
The species of plants from which PSA was recovered, are spontaneous, S. viridis (L.) Beauv., and A. philoxeroides (Mart.) Griseb., and ornamental, P. tomentosa (Thunb.) Steud . The first is an annual herb of the family Poaceae. A. philoxeroides is known as "Alligator weed" for its preference for aquatic habitats and of South American originary; currently it is widely distributed worldwide. P. tomentosa is a deciduous tree native to China where it is popular for edge planting on the road, and now grown as an ornamental tree in parks and gardens throughout the world.
These results can have a deep and unexpected impact on the evaluation of the presence of the pathogen in a specific area and the approach to the kiwifruit bacterial canker control strategies and, consequently, of all the kiwifruit production to avoid PSA spread in orchards or, more concretely, to decrease the amount of natural inoculum.
So, it seems to be relevant to take into account the destruction of weeds, like S. viridis, a real alternative host of PSA, very common in kiwifruit orchards and widely distributed in most major countries kiwi fruit production, such as China, Italy and New Zealand.
For further information:
Prof. Giorgio M. Balestra
DAFNE (Department for Agriculture, Forestry, Nature and Energy)
University of Tuscia
Via S. Camillo de Lellis
01100 Viterbo
Ph.: +39 0761 357474
Mob.: +39 333 4246404
Fax: +39 0761 357473
Email: [email protected]
Web: www.unitus.it