RESISTANCE REACTIONS OF LEAVES AND TUBERS OF ROLC TRANSGENIC TETRAPLOID POTATO TO BACTERIAL AND FUNGAL PATHOGENS - CORRELATION WITH SUGAR, STARCH AND CHLOROPHYLL CONTENT

Infection of plants with Agrobacterium rhizogenes results in the hairy root disease. Four different loci (rolA, B, C, D), located on the TL-DNA of the Ri plasmid are involved in the establishment of this disease. When the rolC gene was expressed alone in tetraploid potato plants, the transgenic plants displayed severe phenotypic and physiological alterations compared to untransformed controls. Therefore we have tested their resistance reaction to pathogens and found differences after the introduction of this foreign gene. The level of infection was correlated to contents of some leaf and tuber metabolites. A new bioassay was used to measure the resistance of leaves and tubers. The pathogens used were the fungi Alternaria alternata and Botrytis cinerea, and the bacterium Erwinia carotovora subsp. atroseptica. On leaves, the mean level of infection with both fungi was between 10 and 20% in both controls, whereas in rolC transformed potato clones the infection increased significantly up to 95%. The correlation between level of infection of the two fungi was high and significant. The infection level was positively correlated with fructose and glucose content. However, in tuber discs of all rolC potato clones the mean level of infection was lower (between 15 and 55%) than in the controls (between 75 and 95%). Measurements of the tuber content of the metabolites studied in leaves revealed a positive correlation of the infection level with glucose, dry matter and starch content. Considering together the results obtained with leaves and tubers, only glucose content was positively correlated with infection rates. © 1993 Academic Press, Inc.