Occurrence and pathogenicity of Pseudomonas fluorescens and P. putida on tomato plants in Italy

During 2006-2008, a survey conducted in soilless and soil-grown tomato crops in eastern and southeastern Sicily (Italy) disclosed the presence of widespread leaf chlorosis and necrosis associated with yellow, pink or brown discolouration of vascular and pith tissues. Bacteria were always isolated from symptomatic tissues on KB and NA media. A total of 158 isolates showed the LOPAT characters of group Va (-+-+-) and group Vb (++-+-) and 21 of these strains were identified as different biovars of Pseudomonas fluorescens and P. putida. Koch’s postulates showed that 42 fluorescent Pseudomonas isolates are able to induce vascular discolouration of tomato plants but not leaf chlorosis and necrosis. The interactions of vascular infections and abiotic stresses were studied in growth chamber experiments. Differences in virulence were found among P. fluorescens biovar I and P. putida bv. A strains on tomato plants grown under saline stress conditions. Both bacteria were able to induce leaf chlorosis, necrosis or death of tomato plants under saline stress conditions.