EFFECTS OF SIMULATED RAIN ON PSEUDOMONAS SYRINGAE pv TOMATO POPULATIONS ON TOMATO PLANTS
L. Pietrarelli, G.M. Balestra, L. Varvaro
A rain simulator was developed to study the effects of rain on the biological and the epidemiological aspects (distribution, epiphytic survival) of Pseudomonas syringae pv. tomato populations in the tomato canopy. Two different kinds of rain were simulated. Rain events, relative humidity, drip-irrigation and temperature were automatically controlled and monitored in a growth chamber. Simulated rainfall intensity varied with nozzle size, water pressure at the nozzle, and height of the nozzle above the plot surface. Spray nozzles formed drops of 1.6 mm or 2.7 mm in diameter. Rain was simulated on tomato plants already colonized by P. s. pv. tomato (plants with speck symptoms where bacteria were inoculated 5 days before the rain event) and on plants not colonized by the pathogen (inoculated 3 h before the rain event). After each rain simulation, the horizontal and vertical distribution and epiphytic survival of P. s. pv. tomato were observed, for two weeks. Drops 2.7 mm in diameter were more effective in distributing bacteria over short distances and drops 1.6 mm in diameter more effective in long-distance distribution. Higher rain intensity reduced epiphytic survival of P. s. pv. tomato when the host-pathogen relation was precarious (noncolonized tomato plants) but when the pathogen was already established (colonized plants), higher rain intensity increased bacterial growth.