Itay: Psa returns to kiwi orchards

Over the past few weeks, all kiwi orchards have experienced a return of bacteriosis, caused by Pseudomonas syringae pv. actinidiae (PSA). This event caught both producers and technicians by surprise, especially as there had been no prolonged rainy periods during winter.

This phenomenon is probably due to the cold temperatures that swept through the peninsula in winter. A study conducted a few years ago actually showed how PSA is favoured by cold temperatures. The study reproduced both the intensity and length of the frosts that hit the Latina area in November 2007 and February 2008. Green and golden kiwi plants were inoculated a month before the frost with a strain and, in the 24 hours after the frost, inoculation points showed copious exudate emissions. The first bacteriosis epidemic was registered in Latina in the spring of 2008.

Kiwi plants subjected to frost conditions and inoculated with PSA. The day after the frost, exudates appeared from the points of inoculation. When such situations occur in orchards, they favour a further spread of the bacteria.

The fact that there were no symptoms this year can be explained by the fact that PSA is mainly an endophytic bacteria that cannot be easily reached by common plant protection products. Frost favours its multiplication and protecting the orchards when plants are not undergoing a period physiological activity is not easy. "Contact" plant protection products are in fact not very effective against diseases residing inside the tree.

For further information:
C.R.A.-Centro di Ricerca per la Frutticoltura
Via di Fioranello, 52
00134 Roma
Tel.: (+39) 06 79348102
Fax: (+39) 06 79340158
Marco Scortichini
Email: [email protected]
Web: www.atlasplantpathogenicbacteria.it