The hormone ethylene is necessary for plant resistance

Dutch phytopathologists have shown that ethylene is vital for the protection of plants against bacteria and fungi. This is another function for the plant hormone already known to play a role in plant aging and fruit ripening.

Bart Geraats from Utrecht University demonstrated that plants which are insensitive for the hormone ethylene are hypersensitive to various microorganisms. The research implies that farmers and horticulturalists must be careful with substances that inhibit the effect of ethylene. Such substances could increase the susceptibility of plants to pathogens.

The researchers produced modified tobacco plants which were insensitive to ethylene. These plants were spontaneously diseased and wilted when grown in ordinary compost. Various fungi and fungi-like microorganisms in the compost attacked the ethylene-insensitive tobacco. These microorganisms do not usually cause diseases in unmodified plants.

Furthermore, various tobacco pathogens caused considerably more damage in the modified than in the unmodified tobacco plants.

This showed that plants must be able to detect ethylene in order to protect themselves against infections caused by various microorganisms.

Efforts to make the ethylene-insensitive plants more resistant were not successful. The administration of chemical substances which normally activate disease resistance in plants provided no increased resistance to the microorganisms in the compost. Treating the roots with harmless or even ’healthy’ bacteria gave no protection either. These bacteria should have competed with the pathogenic microorganisms or could even have increased the disease resistance of the plants.

Ethylene therefore appears to play a key role in activating the resistance mechanism against infectious microorganisms.

For further information please contact Bart Geraats (Department of Phytopathology, Utrecht University), tel. +31 (0)30 2536857, fax +31 (0)30 2518366, e-mail: b.p.j.geraats@bio.uu.nl. The doctoral thesis will be defended on 17 March 2003. Mr Geraats’ supervisor is Prof L.C. van Loon.