EVALUATION OF RESISTANCE TO PSEUDOMONAS-SOLANACEARUM IN POTATO UNDER CONTROLLED CONDITIONS

Potato plantlets derived from in vitro propagation of three cultivars known for their field resistance (Cruza 148 and BR-63.65) or susceptib ility (Desiree) to Pseudomonas solanacearum E.F. Smith were artificial ly inoculated under controlled conditions. The aim of this work was to determine the optimal inoculum concentration and the best observation period in which the cultivars would show different reactions to bacte rial infection as expected on the basis of their field performance. A suitable statistical analysis of disease indices is proposed to distin guish between resistant and susceptible responses, with a particular c are for the applicative needs and a univocal interpretation of the res ults. In order to evaluate the significance of sources of variation re lated to the observed mean differences, the analysis of variance and a convenient clustering procedure of disease index means were applied. The statistical analysis revealed that, under our conditions, an inocu lum concentration of 5 x 10(6) cfu/plant was suitable for separating r esistant from susceptible responses, in accordance with the reactions already observed in field experiments by other authors. Also, differen ces among the three cultivars were best observed nine to twelve days a fter inoculation with the pathogen.