The interaction between Glomus intraradices and Pratylenchus coffeae on transformed carrot roots was studied in root organ culture. G. intraradices provided the roots with increased protection against P. coffeae by suppressing nematode reproduction in the roots. The internal and external mycorrhizal development was not influenced by the presence of the nematodes.The effects of arbuscular mycorrhizal fungi (AMF) on damage caused by root nematodes have been widely addressed (2, 21, 23). However, most research so far has been conducted under greenhouse conditions, with potentially misleading results due, in part, to the presence of undesirable contaminants (3). In recent years, the development of the root organ culture (ROC) system has opened new avenues to study various aspects of the symbiosis (for a review, see reference 13). Numerous studies have been dedicated to interactions between AMF and bacteria and fungi (3,4,12,18), while interactions with nematodes were seldom considered. One recent study reported the effect of AMF on the reproduction and root infestation of the nematode Radopholus similis by using this ROC system (10), but no data reported the impact of this nematode on the fungus development within and outside the host root. Since both organisms are obligatorily dependent on the root for the completion of their life cycle and occupy the same ecological root niche, each may impact the development of the other, either directly or indirectly. This communication reports, for the first time, the development and interaction of the obligatory parasitic nematode, Pratylenchus coffeae, and the obligatory AMF symbiont, Glomus intraradices, under ROC conditions.Transformed carrot roots (Daucus carota L.) colonized with G. intraradices Schenck and Smith (MUCL 41833) and nonmycorrhizal transformed carrot roots were purchased from GINCO (Louvain-la-Neuve, Belgium). Both materials were provided in petri dishes on the modified Strullu-Romand (MSR) medium (reference 7, modified from the description in reference 25). The petri dishes were maintained in an inverted position in the dark at 27°C. To obtain enough transformed carrot roots for the experiment, the root cultures were multiplied by transferring individual 70-mm-long root tips to new petri dishes containing MSR medium every 3 weeks. The AMF cultures were incubated for 5 months in order to obtain enough AMF spores for the inoculation. Several thousand spores were produced within this period and isolated by solubilization of the MSR medium (8), previous to the experiment.A P. coffeae population from Ghana (originally isolated from Musa spp.) was maintained on Medicago sativa L. callus, grown on modified White's medium (11). Nematodes were extracted from the callus with a modified Baermann funnel (15).At the beginning of the experiment, 48 90-mm-diameter petri dishes were filled with 40 ml of MSR medium. In each petri dish, one 70-mm-long transformed carrot root was transferred on the medium. Subsequently, they were separated in two homogenous groups (i.e., two g...