Gerson Luís dos Santos Rodrigues Júnior

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.

O Brasil é o maior produtor mundial de soja, porém a ocorrência de fitonematoides representa um dos principais fatores limitantes à produtividade da cultura. Entre as espécies migradoras mais frequentes destacam-se Pratylenchus brachyurus e Helicotylenchus dihystera, que frequentemente ocorrem em populações mistas em áreas de produção. Este estudo teve como objetivo avaliar a hospedabilidade de cultivares comerciais de soja a populações mistas de P. brachyurus e H. dihystera, bem como sua relação com parâmetros de produtividade. Doze cultivares foram avaliadas em experimento de campo conduzido em área naturalmente infestada, em delineamento de blocos ao acaso, com quatro repetições. Aos 60 dias após a emergência foram quantificadas as populações de nematoides em raízes, enquanto a produtividade e a massa de mil grãos foram determinadas ao final do ciclo das cultivares. Houve diferenças significativas na hospedabilidade entre as cultivares para ambas as espécies. TMG 7058 IPRO, NA 5909 RG, TMG 2165 IPRO e NEO 610 IPRO apresentaram consistentemente as menores populações de H. dihystera e P. brachyurus, enquanto CZ 15B70 IPRO, BMX GARRA IPRO e BMX COMPACTA IPRO apresentaram as maiores populações totais de fitonematoides. Entretanto, as populações de nematoides não apresentaram correlação significativa com a produtividade ou a massa de mil grãos. Os resultados demonstram que cultivares de elevado desempenho agronômico podem diferir quanto à capacidade de sustentar a multiplicação desses fitonematoides, reforçando que a recomendação de cultivares para áreas infestadas deve considerar simultaneamente a produtividade e a hospedabilidade como componentes do manejo integrado de nematoides.

African iris ( Dietes bicolor ) is a rhizomatous ornamental plant widely used in landscape design. In 2025, plants showing chlorosis, reduced development, and root galls typical of Meloidogyne spp. were observed in a nursery in Santa Maria, Rio Grande do Sul, Brazil. Eggs and second‐stage juveniles (J2) were extracted from symptomatic roots, with an average density of 327 eggs and J2 per gram of root. Adult females collected from infected roots were used for isoenzymatic characterisation. Individual females were macerated in sucrose–Triton X‐100 buffer and analysed by polyacrylamide gel electrophoresis. The resulting esterase profile exhibited the characteristic J3 phenotype, identifying the population as Meloidogyne javanica . For molecular confirmation, DNA was extracted from single females, and PCR amplification using the species‐specific primers Fjav/Rjav consistently amplified the expected ~670 bp SCAR fragment. Pathogenicity was verified by inoculating healthy D. bicolor plants with 2,500 eggs. After 60 days, the reproduction factor was 2.1, and symptoms matched those observed in naturally infected plants, fulfilling Koch's postulates. This is the first report of M. javanica parasitizing D. bicolor in Brazil and, for the best of our knowledge, the first global record of this host–nematode association.