Detection, identification, and characterization of rattail cactus necrosis-associated virus (Tobamovirus muricaudae) infecting <i>Opuntia leucotricha</i>, and a preliminary report of that and other Tobamovirus in cacti cultivated in Brazil

• Ano de defesa: 2026
• Autor(a) principal: Guimarães, Jandson José do Vale
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertacoes da USP; Universidade de São Paulo; Escola Superior de Agricultura Luiz de Queiroz
• Palavras-chave em Português: <i>Virgaviridae</i>; Cactaceae; Pera-espinhosa; Viroses; Prickly pear; Viruses
• Link de acesso: https://teses.usp.br/teses/disponiveis/11/11135/tde-08052026-133848/

The Cactaceae family gathers species known as cacti, which have relevance, especially in the northeast and southeast regions of Brazil. In an exploratory approach, rattail cactus necrosis-associated virus-RCNaV and other possible tobamovirus isolates have been detected in different cacti species, especially ornamentals. In the present work, we provide details on the detection and characterization of Brazilian isolates of RCNaV, and a report of the occurrence of additional tobamoviruses infecting Cactaceae species in Brazil. Tobamovirus-like particles were detected in negatively stained cladodes extracts from an asymptomatic prickly pear (Opuntia leucotricha DC) plant by transmission electron microscopy (TEM). Large aggregates of rod- like particles were also visualized in sections of the cladode\'s cortical cells. Total RNA of the cladode of this plant was extracted, purified, and sequenced by NGS, followed by bioinformatical analyses. A primer pair was designed and RT-PCR reactions were performed, generating a 903-bp fragment corresponding to the movement protein (MP) and coat protein (CP) genes. The generated amplicons (GenBank accession no. PQ634414) were sequenced by the Sanger method and, after a BLASTn analysis revealed that the isolate shared 100% and 99% nucleotide sequence identity with RCNaV_BR1 and the South Korean isolate (GenBank accession no. NC016442), respectively. The RCNaV-BR1 isolate was mechanically inoculated in plants of <i>Chenopodium amaranticolor</i>, <i>C. quinoa</i>, <i>Datura stramonium</i>, and <i>Gomphrena globose</i>. Except the latter that remained symptomless, all the other reacted with necrotic or chlorotic local symptoms. The virus was also transmitted by grafting to one plant of dragon fruit (<i>Selenicereus</i> spp.), jurubeba (<i>O. brasiliensis</i>), and <i>Epiphyllum</i> sp. which remained symptomless. About the host range, plants from different botanical families were inoculated, but only <i>C. amaranticolor</i>, <i>C. quinoa</i>, and <i>D. stramonium</i> eacted with symptoms. The presence of the RCNaV in the inoculated plants was confirmed by RT- PCR and TEM analysis. In the phylogenetic analyses, the Brazilian isolate was clustered closely with isolates from South Korea. Besides, this isolate was detected in 18 other cacti samples by RT-PCR and, in most cases, its presence was confirmed by TEM. In biological assays, the isolate was transmitted from these samples to <i>C. amaranticolor</i> and C. quinoa. Using a universal primer pair, other possible isolates were detected by RT-PCR (in 19 samples), such as Sammons Opuntia virus (SOV) that, after sequencing and BLASTn analysis of a sample of this work, revealed that the contig exhibited 100% of similarity to the SOV isolate from the Netherlands. This is the first report of detection, identification and characterization of other possible tobamovirus isolates in cacti in Brazil, beyond RCNaV_BR. These findings represent a crucial step toward understanding their distribution and expanding phytopathological knowledge, thereby helping to reduce the risk of epidemic emergence in other economically important crops, such as dragon fruit and forage palm.