Influence of cultural practices on the incidence and severity of kiwifruit bacterial canker

The bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae, is considered one of the most severe diseases affecting several cultivated Actinidia species, including A. chinensis and A. deliciosa. Kiwifruits have been always considered fruit with an high intrinsic quality due to the strong nutraceutical value, but also to the absence of contaminants such as pesticide residues. With the emergence of this devastating disease, the use of pesticides rapidly increased and therefore the kiwifruit quality can be maintained only by ensuring agricultural practices that reduce the need of toxic xenobiotic compounds. The aim of this study was to provide an in-depth understating of the influence of agricultural practices on disease development and spread and to harmonise the agricultural practices with the current disease control inputs. Therefore, the role of fertilization, irrigation, use of bio-regulators, rootstock, training system and pruning on the incidence and epidemiology of PSA were examined. Nitrogen fertilization had a direct effect on the pathogen's endophytic growth. Furthermore, the depletion of some micronutrients, such as iron, increased the disease. The water stress consequent to a reduced irrigation resulted in higher symptoms. Concerning pruning, the open cuts remains a possible entry point for more than 30 days. In addition, the pruning performed in late season resulted more risk for infection. To test curative pruning, preliminary data were collected on the migration rate of Psa inside the different plant organs. Among the different training system evaluated in this study, the gender double curtain the allowed a more efficient penetration of the phytosanitary treatments that may increase the disease control. However, no differences on disease incidence were observed. Concerning the use of bioregulators, synthetic gibberellin, such as forchlorfenuron, reduced in controlled condition both the disease incidence and severity. Synthetic auxins, on the other hand, showed a detrimental effect with higher symptomatology. In field conditions, none of the used bioregulators showed any effect on the disease incidence and development. Several species were tested for their susceptibility to Psa in order to develop a tolerant rootstock. Arguta spp. resulted the most tolerant to the disease and further experiments are need to test its possible exploitation as a commercial rootstock. Finally, the a preliminary guideline harmonizing the best cultural practices with the most widely used control methods (i.e resistance inducers and copper) is provided.