First report of Alternanthera mosaic virus infecting Pereskia aculeata in Brazil.

Pereskia aculeata Miller is a climbing cactus, native to native to tropical areas of the Americas, whose leaves are used in cooking and folk medicine. Known as "Barbados gooseberry", "leaf cactus" and "ora-pro-nóbis" (OPN), it is considered an unconventional food plant, valued for its high protein and mineral content, offering sustainable healthy food options. In 2024, three OPN plants displaying ringspots, mosaic and leaf distortion were collected in a vegetable garden at the Instituto Biológico, São Paulo, Brazil. Elongated and flexuous particles were observed in negatively stained extracts from OPN symptomatic leaves under a transmission electron microscope (TEM). Ultrathin sections of these tissues revealed the presence of aggregates of elongated particles, presumably viral, and unknown crystalline structures in epidermal and mesophyll cells. RNA extracts were isolated using TRIzol® (ThermoFisher Scientific) and analyzed by high-throughput sequencing (HiSeq 2500 Technology, 2x150 nt paired-end reads, Illumina, San Diego, CA, USA). Bioinformatic analyses of the generated library (15.9 million row reads) revealed the complete genome (6,652 nucleotides, GenBank accession PQ650655) of an isolate of Alternanthera mosaic virus (AltMV, Potexvirus alternantherae) with a mean coverage of 14.000x. This Brazilian isolate, named AltMV_BR1, shared 94.7% nucleotide sequence identity with the genome of AltMV isolates detected in a phlox (Phlox stolonifera) plant identified in the state of Pennsylvania, USA (RefSeq NC_007731). For validation, RNA extracts from the original samples were tested by RT-PCR using primers (Potex5: 5'-CAYCARCARGCMAARTGAYGA-3'/ Potex1RC: 5'-TCAGTRTTDGCRTCRAARGT-3') designed to anneal in the RdRp gene of potexviruses (Van der Vlugt and Berendsen 2002). Amplified fragments (expected size of 735 bp) were sequenced (GenBank accession PQ811939) and the presence of the AltMV was confirmed. The host range of this isolate was evaluated by mechanical inoculation on several cactus species, including OPN, as well as indicator plant species previously described as hosts of AltMV. OPN plants showed mosaic and leaf distortion, whereas Pereskia grandifolia plants expressed local necrotic rings and systemic chlorotic rings. Dragon fruit (Hylocereus undatus) and orchid cactus (Epiphyllum sp.) plants were infected but remained asymptomatic. Necrotic local lesions were observed on Gomphrena globosa. Local chlorotic lesions were detected on Chenopodium amaranticolor and C. quinoa, which developed into systemic infections on plants of both species. Amaranthus viridis and Portulaca oleracea plants also developed infections, resulting in systemic chlorosis and leaf crinkling, respectively. The presence of the virus in these hosts, as well as in the original host, was confirmed with a specific polyclonal antiserum (kindly provided by Dr. J.E. Thomas, Queensland Horticulture Institute, Australia) against AltMV by PTA-ELISA and TEM through detection of elongated particles typical of those produced by potexviruses in extracts and tissue sections. AltMV has a wide host range and its occurrence has been reported in several countries, including Brazil. However, in cactaceous plants, AltMV has only been reported to infect orchids in the United States. To date, this is the first report of AltMV in OPN. Surveys of its occurrence in other regions will be carried out to understand the status of this virus in OPN in Brazil.