<i>Oryza glumaepatula</i>, a New Source of Resistance to <i>Meloidogyne graminicola</i> and Histological Characterization of Its Defense Mechanisms

Abstract

<i>Meloidogyne graminicola</i> causes significant damage to rice fields worldwide. Sources of resistance to <i>M. graminicola</i> reported in <i>Oryza sativa</i> are limited. Resistance to this species has been found in other <i>Oryza</i> species such as <i>O. glaberrima</i> and <i>O. longistaminata</i>. This study aimed to evaluate the reaction of four wild species of <i>Oryza</i> from the Embrapa Rice and Bean Germplasm Bank (Goiás, Brazil) to a pool of <i>M. graminicola</i> populations and determine the resistance mechanism in <i>O. glumaepatula.</i> Two genotypes of <i>O. glaberrima</i>, one of <i>O. alta</i>, three of <i>O. glumaepatula</i>, one of <i>O. grandiglumis</i>, one of <i>O. longistaminata</i>, and one of <i>O. sativa</i> (control) were included in the study. The results showed that <i>O. glumaepatula</i> was highly resistant (reproduction factor [RF] < 1). <i>O. glaberrima</i>, <i>O. alta</i>, and <i>O. grandiglumis</i> were considered moderately resistant. <i>O. longistaminata</i> was susceptible, although values of RF remained lower than the control <i>O. sativa</i> 'BR-IRGA 410', considered highly susceptible. Histological observations on the interaction of <i>O. glumaepatula</i> and <i>M. graminicola</i> showed reduced penetration of second-stage juveniles (J2s) when this resistant wild accession was compared with <i>O. sativa</i>. 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 <i>O. glumaepatula</i> 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., <i>O. glumaepatula</i>), are of great interest for use in future breeding programs with <i>Oryza</i> spp.