Distinct flavonoids in Cicer arietinum regulate positive and negative interactions with Mesorhizobium ciceri and Meloidogyne javanica

Legumes can form symbioses with nitrogen-fixing rhizobia. Nodulation begins when host roots exude flavonoids to attract and induce compatible rhizobia. Flavonoids are also necessary for nodule development. In the field, however, rhizobia do not interact with legumes alone. Plant-parasitic nematodes (PPNs), e.g. root-knot nematodes (RKNs) are very successful gall-forming parasites that infect a wide host range, including legumes. Chickpea (Cicer arietinum) is the second most widely-grown legume crop in the world. Mesorhizobium ciceri is the natural rhizobial symbiont of chickpea and Meloidogyne javanica is a broad host-range RKN that successfully infects chickpea. We hypothesise that distinct flavonoids are involved in the chemoattraction of rhizobia and RKNs and development of nodules or galls, respectively. Previous studies suggested some flavonoids could act as nematostatic and nematicidal compounds against RKNs, affecting their motility, gall and egg formation. I will present data showing how some flavonoid compounds could serve as attractants/repellents for both M. ciceri and M. javanica, as well as regulating nodulation and gall development, respectively. Current data show that chrysin, 2-hydroxyflavone and 3-hydroxyflavone are potential flavonoid markers for high nodulation, whereas increased daidzein concentrations could reduce gall formation. Our goal is to establish flavonoid markers in chickpea that are indicative of high nodulation and tolerance towards PPNs.