First report of grapevine asteroid mosaic-associated virus in grapevines in China.

Grapevine asteroid mosaic-associated virus (GAMaV), a member of the genus Marafivirus of the family Tymoviridae, was first described to infect grapevines in California (Abou Ghanem-Sabanadzovic et al. 2003). Since then, GAMaV has been reported from Greece, Japan, Canada, Uruguay, France, Hungary, Italy, Spain, Switzerland and Russia, and also in some free-living grapevines in North America (Kyriakopoulou, 1991; Morán et al., 2021; Reynard et al., 2022; Shvets et al., 2022; Thompson et al., 2021). GAMaV may be associated with grapevine asteroid mosaic disease (Martelli 2014). In August 2022, a grapevine cv. Cabernet Sauvignon exhibiting chlorotic mottling was collected in Ningxia, China. Total RNAs were extracted using RNAprep Pure Plant Plus Kit (DP441, TIANGEN BIOTECH, Beijing), and the ribosomal RNA were removed by the Epicentre Ribo-Zero rRNA Removal Kit (Epicentre, Madison, WI, USA). The ribosomal RNA-depleted RNAs were then used to construct a cDNA library using a TruSeq RNA Sample Prep Kit (Illumina, San Diego, CA, USA), which was sequenced on an Illumina NovaSeq 6000 platform (Biomarker Biology Technology), resulting in 39,297,567 paired-end clean reads (150 nt × 2). Reads mapping to the grapevine genome (GenBank accession no PN40024) were removed using hisat2 2.1.0 software. The 15,003,158 unmapped reads were de novo assembled into 70,512 contigs using the rnaviralSPAdes method in the SPAdes v3.15.3 software with default parameters and analyzed through BLASTn and BLASTx analysis. Five viruses and two viroids were identified: GAMaV (5 contigs), grapevine Pinot gris virus (3 contigs), grapevine berry inner necrosis virus (3 contigs) , grapevine rupestris stem pitting-associated virus (4 contigs), grapevine red globe virus (2 contigs), grapevine yellow speckle 1 viroid (4 contigs) and hop stunt viroid (3 contigs). The five contigs of GAMaV were 352 nt~2, 224 nt in length, which were assembled from 3, 308 reads and shared 85.56%~91.81% nt identity with the genome of the GAMaV isolate GV30 (KX354202) with 93.3% coverage. To further confirm the infection of GAMaV, we designed two pairs of primers, GAMaV-mel1a/1b (5'-CACCTCGCCCCCTACCTTGAC-3'/5'-AAGAGGACGCCTTTGCGGGAG-3') and GAMaV-cp1a/1b (5'-CTAGCGACGACCGCACTGATC-3'/5'-GTCGGTGTACGAGATTTGGTC-3'), which were used to amplify the 329-bp and 440-bp fragments in the helicase (Hel) domain and coat protein (CP) gene of GAMaV genome in RT-PCR, respectively. The amplified PCR products were cloned and sequenced and the two sequences (OQ676951 and OQ676958) showed 91.2% and 93.4% nt identity with the isolate GV30, respectively. Furthermore, 429 grapevine samples of 71 cultivars were collected from 21 provinces and tested by RT-PCR using the above primer pairs. The results showed that 1.4% (6/429) of the samples tested positive, including one 'Autumn seedless' grapevine (Liaoning province), two 'Dawuhezi' (Liaoning), one 'Cabernet Gernischt' (Liaoning) and two 'Cabernet Sauvignon' (Tianjing and Shandong respectively). The partial sequences of the Hel domain (OQ676952-57) and CP gene (OQ676959-61) obtained from the positive samples by sequencing showed 89.1% to 84.5% and 93.6% to 93.9% nt identity with the isolate GV30, respectively. Because these GAMaV-positive grapevines did not show distinct symptoms, GAMaV pathogenicity remains challenging to confirm. This is the first report of GAMaV in grapevines in China, extending the information on its geographical distribution.