Pratylenchus brasiliensis sp. nov. (Nematoda: Pratylenchidae) - an emerging threat to soybean in an important new agricultural frontier in Brazil.

Abstract

Root-lesion nematodes (Pratylenchus spp.) are significant agricultural pests worldwide. From January 2021 to January 2023, 365 root and rhizosphere soil samples were collected in key soybean-producing regions, revealing a new species, Pratylenchus brasiliensis sp. nov., in Brazil's agricultural frontier. Identification employed a polyphasic approach, integrating microscopy, morphometric analyses, and multi-gene phylogenetics. Molecular species delineation targeted the D2-D3 expansion segments of the 28S rRNA gene, the internal transcribed spacer (ITS) rRNA region, and cytochrome oxidase I (COXI) mitochondrial DNA. Females of P. brasiliensis sp. nov. measure 614.25-671.98 µm in length and 26.42-27.34 µm in width, with a ventrally curved body, four lateral lines, a well-developed spermatheca, a vulva at 77-81% body length, and a conical tail with 19-25 annuli. The labial region features three annuli and a robust stylet (17-18 µm) with anchor-shaped basal knobs. Males are shorter (450-550 µm), with curved spicules (15-17 µm) and a bursa extending over the tail. Molecular analysis confirmed P. brasiliensis sp. nov. as closely related to P. bolivianus, P. curvicaudas, and P. vandenbergae. Pathogenicity tests demonstrated its ability to cause necrotic lesions and gallery formation in soybean roots, with reproduction factors (Rf > 1) in major Brazilian soybean cultivars, emphasizing its agricultural threat. The discovery emphasizes the need for surveillance and the development of management strategies to mitigate its impact on soybean yield. Further studies are needed to explore its host range and identify resistance sources in soybean cultivars.