One plus one does not equal two: the interaction of Ditylenchus dipsaci and Fusarium oxysporum f. sp. cepae.
Mary Ruth McDonald - University of Guelph. Katerina Jordan- University of Guelph, Michael Celetti- OMAFRA, Lilieth Ives- University of Guelph
The combination of a nematode and a fungal plant pathogen often results in a synergistic interaction where the disease symptoms or crop losses are greater than expected from either pathogen alone. Anecdotal evidence suggests that basal plate rot in garlic can be caused by the interaction between the nematode, Ditylenchus dipsaci and the fungus Fusarium oxysporum f.sp. cepae (Foc). A pot study under controlled environment conditions was conducted to determine if there was an interaction between these two pathogens on garlic and if the interaction was additive, synergistic or antagonistic. Sprouted garlic cloves were planted into pasteurized soil. Each pot was then inoculated with either 100 fourth stage juveniles of D. dipsaci, 40 ml of 3x105 conidial suspension (60% marcoconidia and 40% microconidia) of Foc, or both. There was also treatments with D. dipsaci applied one week before Foc and Foc applied one week before D. dipsaci. Disease severity (DS) on the garlic bulbs was high (53- 61%) with D. dipsaci alone and the simultaneous inoculation. Hence, no effect of adding Foc. There was an antagonistic relationship when Foc was applied 7 days before D. dipsaci with only 8% DS. Inoculation with Foc alone resulted in 23% DS. Thus there was no synergism, but early infection by Foc reduced the development of basal plate rot, even compared to the fungus alone. All inoculated garlic had lower, but similar, bulb weight than the noninoculated check. Symptoms on the leaves were not closely related to disease severity on the bulbs.