THE ROLE OF RAIN IN THE HORIZONTAL AND VERTICAL DISTRIBUTION OF PSEUDOMONAS PSYRINGAE PV. TOMATO ON HOST LEAVES
GM BALESTRA, L PIETRARELLI and L VARVARO
Dipartimento di Protezione delle Piante, UniversitÓ degli Studi della Tuscia, Via S. Camillo De Lellis, 01100 Viterbo, Italy
Background and objectives
Materials and methods
Results and conclusions
Comparing the two different kinds of rainfall, interesting results were recorded for vertical P. s. pv. tomato distribution. Quantitatively, cells of P. s. pv. tomato were present mainly on the 3rd node leaf level within 3 days; later, bacteria were more easily detected on the 1st node leaf level within the 15th day, especially on the upper leaf surface. Qualitatively, the distribution of P. s. pv. tomato cells on the upper leaf surface (1st and 3rd node leaf level) was limited on the leaf edge within the first 3 days, and afterwards bacterial cells appeared uniformly distributed. On the lower leaf surface, bacterial distribution was on the leaf edge in A2 and A3 areas with both kinds of rain, while in A1, the P. s. pv. tomato cells were uniformly detected even on the lower leaf surface when the largest drops were used.
It appears that the smallest drops are more suitable for long-distance transport and distribution of P. s. pv. tomato cells. The largest drops showed a remarkable influence for a short bacterial distribution (A1), near the inoculum source. The uniform distribution of the pathogen, even on the lower leaf surface in A1, could be caused by more raindrops reaching the 1st node leaf level, directly or indirectly (falling from the superior node leaf level), and subsequently from the aerosol which is generated. Qualitatively, P. s. pv. tomato distribution (especially vertical) could be explained considering the morphological characteristics of tomato leaves, the gravitational forces involved and the different temperatures between the middle and edge of the tomato leaves. The influence of rain on bacterial distribution must be considered in relation to the phases of immigration, emigration, death, and growth of P. s. pv. tomato populations in the host phylloplane.