Italy: PSA: strategies of attack and kiwifruit plants reactions
The study, funded by the Italian Ministry for Agriculture and Forestry (MIPAAF) and developed by the phytobacteriology research group of DAFNE, University of Tuscia (I), in collaboration with the Center for Electronic Microscope (CIME) of the same University and the Centre for Ecosystem Studies, University of Wageningen Holland, was published this month in the prestigious international scientific journal Phytopathology (Authors: Marsilio Renzi, Paul Copini, Anna R. Taddei, Antonio Rossetti, Lorenzo Gallipoli, Angelo Mazzaglia, and Giorgio M. Balestra (2012). Kiwifruit Bacterial Canker in Italy: Anatomical Changes in the Wood and in the Primary Infection Sites. Phytopathology 102, 9, 827-840. http://dx.doi.org/10.1094/PHYTO-02-12-0019-R) where, because of its scientific importance, the same journal has dedicated its cover.
Many aspects of the biology and epidemiology of PSA in the near future will require different and in-depth studies. This research, carried out in Italy, has studied the infection processes and spread of PSA in the xylem and phloem of kiwifruit plants (Actinidia chinensis and A. deliciosa) by carrying out experiments with artificial inoculations and, through studies of Actinidia spp. plants naturally affected by bacterial canker. In particular analyses were carried by histological and dendrochronological techniques as well as by different electronic microscope systems.
The study showed that the bacterium can infect kiwifruit plants through natural openings and lesions.
In naturally infected kiwifruit plants, PSA is present in the lenticels as well as in diseased tissue, phloem below surrounded by lesions in the periderm, highlighting the importance and role of lenticels as entry route used by the bacterium.
Density and dimensions of lenticels on kiwifruit plant, healthy (left) and Psa' diseased (right)..
In cases of advanced stages of Psa infection are observed phloem necrosis often followed by changes in the exchange rates and infections of the xylem vessels.
From the anatomical point of view, infected kiwifruit plants highlight the changes in the wood such as the reduction of the growth rings, a drastic reduction of the vessels and the development of tyloses inside the vessels colonized by PSA.
In open fields, inside kiwifruit plants naturally infected by bacteria, these changes occur within one year after symptoms have been observed at leaf level, indicating a period of several months between the different primary and secondary symptoms.
By dendrochronological methodologies, it was possible to study the action of PSA on kiwifruit cambium revealing its alteration during the growing season.
Once penetrated inside the host, by its ability to colonize the different vessels (xylem and phloem), PSA demonstrates therefore of being able to reach and to survive easily even at the level of the roots, and therefore, the practice of cut at soil level and/or any grafts, of kiwifruit plants already seriously affected by PSA, are useless in eliminating the pathogen and harmful because they promote the survival and subsequent its further spreading.
"Research has the task of producing and disseminating knowledge" says Dr. Balestra coordinator of the research "we are confident that these results make it possible to fully learn fundamental aspects related to the biology and epidemiology of this bacterium, such as the reaction of kiwifruit plants as a result of PSA infection, as to adopt appropriate measures. "
"As always, also in this case the potence of natural elements highlight the precariousness of Man choices" concludes Balestra "Nature always expresses, in positive or negative sense, all his strength and no marketing strategy can substitute any biological processes; natural events can't be arrested, forced or changed, only sometimes accompanied therefore, are particular important the roles of the Governments by their addresses, as those of the kiwifruit organizations, by their balance, to work all together for the interest of the whole kiwifruit chain."
Further info:
Dr. Giorgio M. Balestra - Senior Researcher
DAFNE (Department for Agriculture, Forestry, Nature and Energy) - University of Tuscia
Via S. Camillo de Lellis
01100 Viterbo - Italy
Phone: +39 (0)761 357474
Fax: +39 (0)761 357473
Mob.: +39 333 4246404
Email: balestra@unitus.it
Web: www.unitus.it
Skype: giorba5618
Personal Web: www.agraria.unitus.it/interna.asp?idCat=244