Detection of Aphelenchoides besseyi in Major Rice-Growing Regions of Portugal: Tracing a Possible Introduction...

Aphelenchoides besseyi, the causal agent of the white-tip disease, is a quarantine nematode known to affect rice (Oryza sativa) by colonizing leaf tips and panicles. In January 2021, A. besseyi was detected in Portugal in imported Italian rice seeds (cv. Ariete). Although the contaminated lot was intercepted, subsequent detections in 2022 and 2024 revealed the presence of the nematode in the three main rice-producing regions of Portugal: the Sado, Mondego, and Tagus basins. Morphological and morphometric analyses, supported by molecular characterization using rDNA (18S, ITS1-5.8S-ITS2, and 28S) and mitochondrial (COI) markers, confirmed the identity of the nematodes. Phylogenetic analyses further corroborated these identifications, with sequences showing 98.78 to 100% similarity to known A. besseyi isolates. Pathogenicity tests conducted on rice seedlings (cv. Nipponbare) confirmed the capacity of the isolates to induce typical white-tip symptoms. This study provides the first confirmed report of A. besseyi in Portuguese rice fields and highlights the role of international seed trade in the dissemination of regulated pests. In response, phytosanitary surveillance and containment measures have been enforced under the national rice seed monitoring program. Although follow-up surveys have yielded negative results, suggesting a restricted distribution of A. besseyi, continued surveillance is essential to prevent future introductions.