First Report of Melon Severe Mosaic Orthotospovirus infecting cucurbits in the United States.

Cucurbits (family Cucurbitaceae) includes globally important fruit and vegetable crops. Virus diseases pose a serious threat to cucurbits, limiting crop quality and yield (Regina et al. 2021). In fall 2023, leaf and fruit samples from two squash plants with chlorotic mosaic symptoms and fruit distortion from Monroe and Pope counties in Arkansas were received for diagnosis at the University of Arkansas Division of Agriculture Plant Clinic. Based on symptoms, samples were assessed for melon severe mosaic orthotospovirus (MeSMV) using the ImmunoStrip® developed for detection of the virus (Agdia® Inc., Elkhart, Indiana). The presence of MeSMV was also confirmed by RT-PCR using the Agdia Tospovirus group PCR primers. An amplicon was sequenced and showed 91% sequence identity to the MESMV type isolate (NC_033834, VE440-A). To further verify the results, nucleic acids from a squash sample from Pope County were extracted as described by Poudel et al. (2013), DNase treated, and sequenced on an Oxford Nanopore MinION as described by Liefting et al. (2021). A total of 25,914 raw reads were analyzed using VirFind (Ho and Tzanetakis 2014), which identified 112 reads mapping to the three segments of MeSMV. Primers for all three RNAs were developed and amplified 638, 650, and 1153 nt of the S, M, and L segments of the virus respectively. The amplicons were sequenced bidirectionally and show 89-93% identity to the type isolate from Mexico (GenBank accessions PP301332-4). MeSMV has only been identified in Mexico and can cause significant losses to honeydew melon, zucchini, and cucumber (Ciuffo et al. 2009). Thus, this is the first report of MeSMV outside Mexico. Given the severity of the symptoms observed in cucurbit crops, the virus poses a potential threat to the cucurbit industry in the United States. Growers should be aware of this virus and take the necessary precautions to prevent its spread in the field.

First report of constricta yellow dwarf virus infecting Lobelia in the United States and the world.

Blue cardinal (Lobelia siphilitica L., family: Campanulaceae) is a popular perennial ornamental plant. Lobelia spp. have been reported as hosts of economically important viruses including cucumber mosaic virus (Nameth and Fisher, 2001), turnip mosaic virus (Lockhart et al., 2002), and tomato spotted wilt virus (Brown, 1988). During fall 2022, in a garden in Fayetteville, Arkansas, USA, yellow speckling, chlorosis, and dwarfing were observed on several cardinal plants. Three symptomatic plants were sampled, and RNA was isolated as described in Poudel et al. (2013) and pooled. Material was sequenced using the MinION platform as described by Liefting et al. (2021). A total of 56,700 raw reads (mean-length 326) were analyzed using VirFind (Ho and Tzanetakis, 2014) revealing 23 contigs ranging from 209-12,776 nucleotides (nt) which showed 96.2-98.4% identity with constricta yellow dwarf virus (CYDV; genus Alphanucleorhabdovirus, KY549567) and 16 contigs ranging from 201-531 nt with 83.4-95.7% identity with hydrangea chlorotic mottle virus (HdCMV; genus Carlavirus, EU754720). A total of 6,387 reads were mapped to the CYDV genome (KY549567) with 181x average coverage per nucleotide, and the consensus sequence of 12773 nt shared 98.1% identity to KY549567. The results were verified by RT-PCR and sequencing of the amplicons using primers 8825F: 5'-ACCCTGAGACAGGCATTGTG-3' and L2 9760: 5'-GCCGTACTATGAGAAGGGGC-3' for CYDV and 6495F: 5'-CAAGTACGTCTGTGTGAGGT-3' and 6630R 5'-CTTTTTGATAGTGTCATTGCTACC-3' for HdCMV. RNA was subsequently extracted from eight symptomatic and 12 symptomless samples. All symptomatic samples tested positive for CYDV but none of the 20 was positive for HdCMV indicating that CYDV is possibly the causal agent of the observed symptoms. Amplicons were CYDV specific and showed 91-98% nt identity (99-100% amino acid identity) (accession No. OP998261-63) with the CYDV isolate from Solanum tuberosum (KY549567). To the best of our knowledge, this is the first report of CYDV infecting L. cardinalis in the USA and the world. CYDV has been reported as an important pathogen of potato in the USA and recent reports indicate that emergence and re-emergence of rhabdoviruses on new hosts worldwide may threaten agricultural production (Bejerman et. al., 2021). Given the lack of monitoring of cardinal plants for viruses, this could serve as a reservoir of CYDV for several vegetables and ornamental crops (Jang et al., 2017).