Defense responses of Hevea brasiliensis to elicitors from root rot fungi

Abstract

Elicitation of root defense responses of rubber tree (Hevea brasiliensis) to Rigidoporus lignosus has been performed by injection of fungal cell wall extracts into the root system of 1-month-old seedlings. A time course study showed that tissue lignification is induced at 3, 8, 15, and 45 days after elicitor treatment, as observed under a light microscope. The ethanolsoluble elicitor fractions stimulated cinnamyl-alcohol dehydrogenase activity, involved in lignin synthesis, as well as callose deposits 15 days and 30 days after elicitor treatment. A differential phellogen activity was observed 15 days after injection of roots with fungal extracts not treated with pronase. Stimulation of chitinase activity in leaves, cell hyperplasia, and suberization of root cell walls did not succeed. These data show that some defense mechanisms of tree roots can be triggered by elicitors from root-rotting fungi and result in the stengthening of structural barriers in host tissues. Key words: root rot diseases, elicitation, lignification, cambium stimulation, callose.