Absence of Pseudomonas syringae pv. actinidiae in asymptomatic fruits at harvest in kiwifruit orchards of Emilia Romagna severely affected by the bacterial canker

Italy is the first producer of kiwifruit in the northern hemisphere (excluding China) contributing to 65% of the overall output. Since 1999, in Italy the production capacity of kiwifruit exceeds 500,000 tons and, from ‘90 to date, export of kiwifruit has significantly increased to exceed 70% of the marketable production. To investigate thoroughly whether the fruits themselves, harboring Psa either epiphytic or endophytic, can be a mean of disease spread is of great economic relevance for the production and commercial exchange. In October 2011, in 8 kiwifruit orchards (3: Actinidia deliciosa cv. Hayward; 3: A. chinensis cv. Hort16A; 2: A. chinensis cv. Jin Tao) severely affected by bacterial canker in Emilia Romagna were harvested 8 samples of 100 asymptomatic fruits. In two kiwifruit orchards (A. deliciosa cv. Hayward and A. chinensis cv. Hort16A), not affected by Psa, 2 samples of 100 fruits were used as controls. The Psa presence in the surface and the columellae of fruits was tested by microbiological and molecular analysis. In all fruits samples harvested in orchards with bacterial canker symptoms, the isolations of epiphytic/endophytic bacteria excluded the presence of Psa, and this was confirmed by PCR analysis. Since the fruits tested were collected directly from the plant in the field, it can be assumed that no endophytic fruit colonization occurred in the orchard. Our results support the hypothesis that in orchards Psa is not able to colonize, as epiphyte or endophyte, the fruits at harvest. Therefore it is very likely that the fruits of Actinidia spp. do not represent a risk of pathogen dissemination