Identification, Molecular Characterization, and Distribution of Cucurbit-Infecting Viruses in Texas.

Abstract

Texas is among the top producers of cucurbits in the U.S., but there is little current knowledge on cucurbit-infecting viruses in the state. Consequently, field surveys were conducted in 62 fields (4.1 to 174 ha) across 16 counties over three growing seasons in 2020 and 2021. Visible disease incidence ranged from 0 to 100% in surveyed fields. RT-PCR virus diagnostics were conducted on 241 leaf tissue samples from cucurbit (n=210) and non-cucurbit (n=31) plants, encompassing plants with (n=182) or without (n=59) virus-like symptoms. Metagenomic analysis of sample subsets that represented the spectrum of observed symptoms yielded ~56.7 million single-end raw Illumina reads (75 nt each) that were processed into 177 contigs specific to 14 viruses. Among them, the near-complete genomes of cucurbit aphid-borne yellows virus (CABYV), cucurbit chlorotic yellows virus (CCYV), cucurbit yellow stunting disorder virus (CYSDV), papaya ringspot virus strain W (PRSV-W), squash leaf curl virus (SLCV), squash vein yellowing virus (SqVYV), watermelon crinkle leaf-associated virus 1 (WCLaV-1), WCLaV-2, watermelon mosaic virus (WMV), and zucchini yellow mosaic virus (ZYMV). RT-PCR screening of individual samples revealed varying incidences of the commonly detected viruses; SqVYV (30.3%), SLCV (23.7%), CYSDV (18.7%), WMV (17.4%), PRSV-W (13.7%), WCLaV-1 (11.2%), WCLaV-2 (9.1%), CABYV (7.5%), ZYMV (6.6%), CCYV (6.2%). Mixed infections (40.2% or 97 of the 241) of two to six viruses were greater compared to single infections (33.6% or 81 of the 241). Hidalgo County had the highest number of virus-positive (100% or 44 of the 44) and mixed infected (72.7% or 32 of the 44) samples. While the incidences of PRSV-W, WMV, and SqVYV increased significantly across the successive three seasons, that of SLCV declined. Other cucurbits were preferentially positive for CCYV, CYSDV, CABYV, WMV, ZYMV, and SLCV over watermelon. Whereas watermelons were more likely to be positive for WCLaV-1 and WCLaV-2 than other cucurbits. The survey indicates the occurrence of diverse and potentially yield-limiting viruses in Texas cucurbit fields, as well as seasonal differences and host-type variations in their incidences.