Olive knot disease new insights in the ecology, physiology and epidemiology of Pseudomonas savastanoi pv. savastanoi.

The growth of Pseudomonas savastanoi pv. savastanoi on three selective substrates (ANS-S, PVF-1 and OKA) was studied. On ANS-S, recovery of P. savastanoi was the highest and selectivity the lowest; on OKA it was the opposite (highest selectivity, lowest rate of recovery). Moreover, on OKA the colony morphology typical of the bacterium on the substrates NSA or KB, which are usually used for their growth, was lost. On PVF-1 recovery and selectivity were intermediate between ANS-S and OKA and the colonies of P. savastanoi strains maintained their typical morphology. The spread in Tuscany of levan-positive populations of P. savastanoi and the growth of this bacterium under adverse environmental conditions (poor nutrients and high agar concentration) is also reported. In this connection it was ascertained that P. savastanoi, like other bacteria (Bacillus subtilis, Proteus mirabilis, Escherichia coli, etc.) adapts to hostile environmental conditions by forming complex growth patterns during colony development.