Resistance responses of mycorrhizal Ri T-DNA-transformed carrot roots to infection by Fusarium oxysporum s. sp. chrysanthemi

The influence exerted by arbuscular mycorrhizal fungi in stimulating plant defense reactions was investigated using an in vitro system in which Ri T-DNA-transformed carrot roots were infected with Fusarium oxysporum f. sp. chrysanthemi. This experimental model, based on the use of root-organ culture to obtain typical mycorrhizal infections in axenic conditions, was selected as a reliable means of studying the events associated with subsequent pathogen attack. Cytological investigations of root samples revealed striking differences in the extent of plant defense reactions between mycorrhizal and nonmycorrhizal carrot roots after inoculation with the fungal pathogen