THE SIGNIFICANCE OF EPICUTICULAR WAXES FO R DEFENSE OF PATHOGENS AS SHOWN FOR BOTRYTIS-CINEREA INFECTIONS IN KOHLRABI AND PEA-PLANTS

The effect of the amount and the fine structure of epicuticular waxes on the susceptibility of plants to Botrytis cinerea infection was stud ied in order to document the significance of epicuticular waxes as a d efense mechanism against fungal pathogens. Experiments were conducted under controlled conditions with leaves of two plant species at two di fferent approaches. In Brassica oleracea var. gongylodes epicuticular waxes were damaged by gently brushing or wiping the leaf surface, or r emoved by stripping the leaf surface with cellulose acetate. The degre e of wax erosion was documented by SEM. In Pisum sativum susceptibilit y to B. cinerea infection was evaluated using 3 mutants differing in w ax production. Two of these mutants showed a lower density of epicutic ular wax crystalloids, as confirmed by SEM. Evaluation of leaf lesions induced by fungal infection was performed by rating, measuring chloro phyll fluorescence of the leaves and ethylene production, respectively . There was a strong relationship between the amount of wax or degree of fine structure and the intensity of B. cinerea infection: in kohlra bi the increase of destruction or removal of epicuticular wax and in p eas the decrease of wax crystalloid density resulted in increasing lea f damage as induced by B. cinerea infection. These results clearly dem onstrate that not only the thickness of the epicuticular wax layer but also the three-dimensional fine structure of wax crystalloids may pro vide an efficient barrier against fungal attack.