Biology and Genetic Variability of the Leaf Galling Nematode \u3ci\u3eDitylenchus gallaeformans\u3c/i\u3e

The plant parasitic nematode Ditylenchus gallaeformans induces galls on stems, leaves, and inflorescences of Melastomataceae plants in Central and South America, and the Caribbean. Due to its specificity to Melastomataceae and severity of symptoms, this nematode has been considered as a possible biological control agent against invasive species of Miconia. Little is known about D. gallaeformans biology, genetic differences among populations, and host genotype specificity. I investigated the population structure and genetic differences among populations from Costa Rica, Dominica and Trinidad collected from different host species. Phylogenetic reconstructions, haplotype networks, and analysis of molecular variance showed strong genetic structure among populations from different widely separated locations but no structure that was explained by host plant species. The pathogenicity of different populations of D. gallaeformans was assessed in greenhouse and field studies. I observed that, under the conditions tested, the nematode did not establish well or cause severe symptoms to the plant host. Difficulties in rearing the nematode and causing disease mean that D. gallaeformans is unlikely to be a successful biological control agent against Miconia spp. I also compared the microbiome of healthy and galled leaves, and found that galled leaves have higher bacterial diversity than healthy leaves and that their community composition differs significantly. The genera Burkholderia and Xanthomonas were identified as indicator species for galled leaves, but their role in infection and symptoms development is unknown. Although D. gallaeformans is unlikely to be a suitable biocontrol agent, future work is needed to further understand the pathways of infection of this nematode