Bacterial Composition of Meloidogyne exigua Egg Masses from Symptomatic and Asymptomatic Coffee Plants

Root-knot nematodes (Meloidogyne spp.) threaten global agricultural production. Bacteria that inhabit the nematode egg mass have not been well explored. Using a metataxonomic approach based on sequencing the 16S rRNA gene of bacteria communities associated with Meloidogyne exigua egg masses, we found significant differences in bacterial composition and diversity in the egg masses of symptomatic coffee plants compared with asymptomatic ones for the first time in field conditions. The families Pseudomonadaceae, Burkholderiaceae, Flavobacteriaceae, Rhizobiaceae, Micrococcaceae, and Bacteroidaceae were more abundant in egg masses sampled from asymptomatic plants, and Chitinophagaceae, Glycomycetaceae, Micropepsaceae, Beijerinckiaceae, and Enterococcaceae were more abundant in samples from symptomatic plants. The genera Pseudomonas, Sphingobacterium, Flavobacterium, Corynebacterium, and Virgibacillus were found in greater abundance in egg masses from asymptomatic plants, and only Tumebacillus and Bacillus were significantly more abundant in samples from symptomatic plants. The reproduction and infectivity of M. exigua was tested in tomato plants. The reproduction index of M. exigua (nematodes eggs per gram of roots) was significantly lower when applying nematode inocula from asymptomatic coffee plants compared with inocula from symptomatic plants. The root weight of tomato plants infected with inocula from asymptomatic coffee plants was significantly higher than that of plants infected with inocula from symptomatic plants. However, there was no significant difference in the infectivity index (number of galls per root system) of tomato plants when inoculated with inocula from either source (P ≤ 0.05). This study showed a differential bacterial community colonizing coffee plants with different levels of nematode infections, which opens the door for future nematode biological control.