Influence of plastic tunnel and light quality on the interactions between Pseudomonas syringae pv. actinidiae and kiwifruit

The micro-climatic conditions inside orchards and the vine canopy are critical factors in determining the local severity and extent of the bacterial canker of kiwifruit ( Pseudomonas syringae pv. actinidiae -Psa). Among these conditions, the effect of light quality and intensity has received, so far, little attention. Light intensity and quality are crucial factor influencing plant development, but they may also affect movement, survival and virulence of Psa. The use of plastic covers is an emerging practice showing some effect in reducing Psa incidence and severity. The effect of plastic tunnel is probably related to both a modification of the microclimatic conditions (i.e. a reduction in leaf weatness) and to an increased permanence of control treatments on the leaves. Our study aimed to evaluate the effect of plastic covers on Psa symptom development and on the micro-climatic conditions in the orchard. In this study the use of permanently closed tunnel and seasonal closed tunnel were tested in two infected commercial A. chinensis orchards. The use of permanently closed tunnel showed a positive result in the control of the disease by the reduction of the leaf wetness. Finally, since commercial plastic tunnel might modify light intensity and composition, trials were performed in laboratory conditions to evaluate the effect of light on the bacterium pathogenicity and plant defenses. Concerning Psa virulence, phenotypes and the expression of genes related to motility, biofilm formation and virulence were considered. To evaluate the influence on plant resistance, callose formation, expression of defense related genes and susceptibility were considered.