OpenLB
Open Library of Bioscience

Powdery mildew is widespread on greenhouse-cultivated tomato especially in Europe. Rhizobacteria, particularly Pseudomonas strains are well known for inducing resistance to many diseases on field crops. Plant disease resistance can also be induced by treatment with benzothiadiazole (BTH) which specifically induces the salicylic acid-dependent defence pathway. We investigated the possibility of inducing resistance to Oidium lycopersici on tomato and tobacco by treatment with BTH or with resistance-inducing rhizobacteria. Tomato (Lycopersicon esculentum) cv. Moneymaker and NahG tomato (a transgenic tomato which cannot accumulate salicylic acid (SA)) were planted in soil treated with P. aeruginosa KMPCH, a SA-producing mutant of P. aeruginosa 7NSK2, at 10(8) CFU/g. Four weeks-old plants were inoculated by exposure to an atmosphere heavily infested with O. lycopersici. P. aeruginosa 7NSK2 and KMPCH; and P. fluorescens WCS 417 were similarly tested on tobacco cv. Xanthi and Samsun NN. The results showed that the rhizobacteria had no effect on the levels of infection of the plants by O. lycopersici. There were also no differences between NahG and wild type plants. We conclude that the induced resistance pathways activated by rhizobacteria do not lead to enhanced resistance of tomato and tobacco to O. lycopersici. BTH was tested on tomato by soil application at 0.1 ppm or foliar spray with 100 microM solution 4 or 7 days before inoculation (dbi) and tobacco was treated by foliar spray with 1, 10 or 100 microM BTH, 4 dbi. While a dose-dependent suppression of O. lycopersici by BTH was registered on tobacco, tomato infection by the powdery mildew was not affected by BTH. This difference indicates that BTH probably affects the tobacco-Oidium and the tomato-Oidium systems differently. We are currently investigating whether or not this difference can be associated with the production of different PR proteins.