INDUCED SYSTEMIC RESISTANCE AGAINST SPHAEROTHECA-FULIGINEA IN CUCUMBER - EFFICIENCY OF TOBACCO NECROSIS VIRUS (TNV) AND COPPER-SULFATE (CUSO4) IN ELICITING DEFENSE REACTIONS

Plants of Cucumis sativus were either preinoculated with TNV or treate d with drops of a 5 % solution of CuSO4 on the cotyledons, and 5 days later challenge-inoculated with Sphaerotheca fuliginea on the first tr ue leaf. The induced systemic resistance was assessed by evaluating th e percentage of conidial germination, the length of the hyphae derived from single conidia, the number of cells with lignified walls and tha t of cells containing haustoria. The number of necrotic cells was also recorded. Compared with controls, in TNV-preinoculated plants conidia l germination was lower, hyphal length shorter and the number of haust oria much reduced. The majority of haustoria was found in cells with l ignified walls. Pretreatment with CuSO4, although inducing a slight in crease of cell wall lignification, did not appreciably reduce the infe ction process. The number of necrotic cells was very low in all cases. These results suggest that, in this host/pathogen interaction, hypers ensitive cell death has no part in the induced defence reaction, altho ugh a major role is played by the lignification process.