An increasing the resistance of field tomato to Pepino mosaic virus

A resistance degree of three cultivars: 'Atol', 'Betalux' and 'Promyk' of Lycopersicon esculentum Mill. to the pathogen was investigated. The most susceptible to Pepino mosaic virus (PepMV) turned out to be the 'Betalux' cultivar, therefore it was chosen for further studies. For this cultivar, under the transmission electron microscope, a few particles of the virus were observed in leaves, and many virions arranged in the form of the bundle--in fruits. An influence of two inducers was examined--benzothiadiazole (BTH) dissolved in the water and chitosan dissolved in the acetic acid as well as the influence of milk with the addition of the acetic acid on the degree of the disease development. Different testing methods were applied: measuring the percentage of leaf surface covered by necroses and yellow spots as well as the percentage of infected area on fruits, detecting the presence of 3.3'-diaminobenzidine peroxidase, hydrogen peroxide and lignin in leaves with colourful histochemical reactions. It was stated that the 0.5 mM solution of BTH induced the highest increase in the systemic acquired resistance (SAR)--mainly in fruits, which were least infected by the virus. The upper leaves, growing above the BTH treatment zone, were also highly protected. The milk with the acetic acid had no influence on improving the condition of younger leaves (growing above the level of sprayed leaves). However, it contributed in a high degree, though a little bit lower than in case of BTH, to the protection of the tomato fruits. Natural resistance of the 'Promyk' cultivar is correlated with the higher level of hydrogen peroxide, the higher activity of the peroxidase and the greater accumulation of the lignin than in case of the susceptible cultivar--'Betalux'. BTH induced defensive reactions at susceptible cultivar of the tomato, which correlated with an increase in the level of the above mentioned indicators of plants resistance, especially of hydrogen peroxide.