Many species of morning glories (Convolvulaceae) form symbioses with seed-transmitted fungal endosymbionts in the genus Periglandula, which produce ergot alkaloids within the plant and may contribute to plant-fungal defensive mutualisms. Allocation of seed-borne ergot alkaloids to various tissues of several Ipomoea species has been demonstrated, including roots of the I. tricolor. The objective of this study was to determine if infection of I. tricolor by the fungal endosymbiont affects Southern root-knot nematode (Meloidogyne incognita) gall formation and host plant fitness. In particular, we hypothesized that I. tricolor plants infected by the Periglandula endosymbiont (E+) would have fewer nematode-induced galls on the root system compared to non-symbiotic plants (E-). E+ or E- status of plant lines was confirmed by grinding individual seeds and testing methanol extracts for ergot alkaloids. To test the effects of Periglandula on nematode colonization, E+ and E- I. tricolor seedlings were potted in soil infested with high densities of M. incognita nematodes (N+) or no nematodes (N-). All plants (N=18 per treatment) were then grown in the greenhouse for four weeks before harvesting when nematode colonization was visualized microscopically and total gall number and plant biomass were quantified.
Results/Conclusions
Ergot alkaloids were quantified in I. tricolor roots of E+ and E- plants. Four ergot alkaloids were detected in roots of E+ plants, but no alkaloids were found in roots of E- plants. In parallel, we found that nematode gall formation was significantly lower in E+ plants compared to E- plants, independent of root biomass. We also found significant differences in total plant biomass between both the nematode and endosymbiont treatments. Both N+ plants and E+ plants had significantly reduced biomass compared to N- and E- plants, respectively. These results demonstrate the Periglandula endosymbiont’s potential defensive role against biotic enemies and inform potential applications for agricultural pest management.