Occurrence and distribution of plant-parasitic nematodes in flooded rice-producing regions of Rio Grande do Sul, Brazil

Abstract Rice ( Oryza sativa L.) is a crop of great economic and social importance for many countries around the world. Brazil is among the countries with the highest rice production in the world, and the state of Rio Grande do Sul accounts for more than 70% of national production. However, biotic threats, including plant-parasitic nematodes, may limit rice production across the state’s producing regions. This study surveyed the occurrence and genus composition of plant-parasitic nematodes in irrigated rice fields across different regions of Rio Grande do Sul. Fifty-four composite soil and root samples were collected and processed for nematode extraction. Nematodes were identified to the genus level based on morphological characters, and their diversity, abundance, and relative frequency were determined for each region. Differences in plant-parasitic genus composition in soil and roots were tested using permutational multivariate analysis of variance. No significant differences were detected among rice-producing regions in the composition of plant-parasitic nematode genera in soil and roots ( p > 0.05). When comparing the influence of soils with higher and lower drainage capacity, only the genus Helicotylenchus had its abundance reduced in soils with lower drainage ( p < 0.05). Six nematode genera associated with plants were detected: Meloidogyne , Hirschmanniella , Aphelenchoides , Pratylenchus , Helicotylenchus , and Mesocriconema . Meloidogyne was the most geographically widespread genus, occurring across the sampled municipalities. However, the detection of five additional genera reveals a far more diverse nematode complex in irrigated rice than previously recognized. These results expand our regional characterization of plant-associated nematodes, underscoring the importance of monitoring the entire assemblage in crop protection and surveillance.