Meloidogyne graminicola causes significant damage to rice fields worldwide. Sources of resistance to M. graminicola reported in Oryza sativa are limited. Resistance to this species has been found in other Oryza species such as O. glaberrima and O. longistaminata. This study aimed to evaluate the reaction of four wild species of Oryza from the Embrapa Rice and Bean Germplasm Bank (Goiás, Brazil) to a pool of M. graminicola populations and determine the resistance mechanism in O. glumaepatula. Two genotypes of O. glaberrima, one of O. alta, three of O. glumaepatula, one of O. grandiglumis, one of O. longistaminata, and one of O. sativa (control) were included in the study. The results showed that O. glumaepatula was highly resistant (reproduction factor [RF] < 1). O. glaberrima, O. alta, and O. grandiglumis were considered moderately resistant. O. longistaminata was susceptible, although values of RF remained lower than the control O. sativa ‘BR-IRGA 410’, considered highly susceptible. Histological observations on the interaction of O. glumaepatula and M. graminicola showed reduced penetration of second-stage juveniles (J2s) when this resistant wild accession was compared with O. sativa. An intense hypersensitivity response-like reaction occurred at 2 days after inoculation in the root cortex of the resistant accession. Few J2s established in the central cylinder, and rare collapsed giant cells were observed surrounded by degenerate females. Fluorescence microscopy in O. glumaepatula revealed giant cells and the female body presumably exhibiting accumulation of phenolic compounds. Our study suggests that wild rice accessions, especially from the AA genotype (e.g., O. glumaepatula), are of great interest for use in future breeding programs with Oryza spp.

Summary The rice root-knot nematode, Meloidogyne graminicola, has been reported in Southeast Asia, China, India, South Africa, USA, Brazil, and other countries. Recent surveys in Southern Brazil showed that M. graminicola was widespread in irrigated rice in Rio Grande do Sul, Santa Catarina and Paraná states, and the presence of a species complex with a predominance of M. graminicola (Est VS1 = G1) and other variants showing similar esterase phenotypes (Est G2 = R2, G3 = R3). Meloidogyne oryzae (Est O1) and M. ottersoni (Est Ot0) were also part of this complex and were recently re-described and detected on rice. The present study provides an integrative taxonomy approach of the typical and atypical populations of M. graminicola on the basis of morphological, morphometric and molecular data. Considering morphological and morphometric features, the two atypical populations (Est G2 and G3) are in close agreement with the description of M. graminicola. Based on the molecular characterisation, populations G1, G2 and G3 were successfully amplified by M. graminicola SCAR markers, although the specificity of these markers was questioned. Phylogenetic relationships complemented and confirmed the other studies. In maximum likelihood analysis of ITS, D2-D3 rRNA and COXII-16S rRNA sequences, all populations of M. graminicola from different esterase phenotypes clustered together with other M. graminicola populations, thus confirming that these enzyme phenotypes (G1, G2 and G3) are related to the same species. A high level of intraspecific variability was detected among all populations, but no correlation between genetic variability and geographic origins occurred.

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