Occurrence of pith necrosis caused by Pseudomonas fluorescens on tomato plants in Turkey

Pith necrosis, caused by Pseudomonas corrugata, P. viridiflava, P. fluorescens and P. mediterranea, is one of the most destructive diseases of tomato in Europe. Pith necrosis of soil-grown greenhouse tomatoes was observed in Adana, Mersin, Antalya, Mugla and Izmir, in the Mediterranean and Aegean regions of Turkey, during late winter and spring of 2002 and 2003.

Symptoms were yellowing and wilting of lower leaves which progressed upwards, brown areas on stems (Fig. 1) and yellow-brown discoloration of the pith (Figs 2 & 3). Bacteria were consistently isolated from affected plants and these formed fluorescent colonies on King's medium B. Twenty-seven bacterial isolates were purified and used for further studies. In tests performed according to Lelliott & Stead (1987), all isolates were Gram negative, oxidase, arginine dihydrolase and gelatin liquefaction positive. None caused soft rot on potato slices within 48 h at 25°C or produced levan-type colonies on sucrose nutrient agar and all were negative in tobacco hypersensitivity and nitrate reduction tests.

Fatty acid (FA) analysis identified the isolates as P. fluorescens biotype I with similarity indices of 55 to 97% (Janse et al., 1992). Isolates were divided into two main clusters on the basis of the FA analysis. Pathogenicity was tested on 4-week-old tomato plants (cv. H-2274) by injecting a 108 cfu per ml suspension of bacteria into the pith, using a hypodermic syringae. A reference strain of P. fluorescens biotype I (CFBP 2101, France) and saline were used as positive and negative controls respectively. Inoculated plants and saline-inoculated controls were covered with polythene bags for 24 h and maintained in a controlled environment room at 25°C, 70% relative humidity, with a 16 h photoperiod. Pith necrosis symptoms developed on inoculated plants in 7 days. No symptoms developed on negative control plants. The bacteria were re-isolated from the inoculated plants and characterised as identical to the reference strain. No differences in the pathogenicity of the isolates were observed. Pith necrosis of tomatoes caused by Pseudomonas corrugata has been reported previously in Turkey (Demir, 1990) but this is the first report of Pseudomonas fluorescens biotype I causing the disease in Turkey.