Melon necrotic spot virus (MNSV) is a member of the genus Carmovirus in the family Tombusviridae. MNSV is naturally transmitted by the soil-inhabiting fungus Olpidium radicale and by seeds and can also be transmitted by mechanical inoculation (Gonzalez-Garza, 1979). MNSV infects mainly cucurbits including melon (Cucumis melon), watermelon (Citrullus lanatus) andcucumber (Cucumis sativus) and causes necrotic spots on leaves, stems and fruits as well as curled and wilted symptoms on leaves (Gonzalez-Garza, 1979). MNSV was originally reported in Japan (Kishi, 1966) and is widely distributed in Asia, Europe, and North America (Herrera et al., 2010). In China, MNSV was first reported in melon in Jiangsu Province in 2008 (Gu et al., 2008) and then occurred in Hami melon in Xinjiang Province in 2014 (Ref. to GenBank KP406627). During October of 2014, necrotic spots and curled symptom as well as mosaic, mottled and/or crinkle symptoms occurred on watermelon and melon in greenhouses in Tai’an city in the Shandong Province, China. To identify the potential existence of MNSV in these samples, total RNAs were extracted from diseased leaves using Trizol reagent, and then reverse transcription was performed using M-MLV reverse transcriptase with primer MN-1937-R (5-GTCTCCAGTGCCTTACCATGTC-3), complementary to the middle region of RNA-dependent RNA polymerase (RdRp) gene of MNSV. The reverse transcripts were used as template to amplify by PCR the potential fragment of 911-1937 of MNSV using primers MN-1937-R and MN-911-F (5-CTCGCTGGGTTCTGTACTTCG-3), corresponding to RdRp coding region of MNSV. PCR products with the size of about 1000 bp were detected in samples of watermelon and melon. The purified fragments were cloned into pMD18-T (Takara) and sequenced using universal primers M13F and M13R. Blast analysis of obstained sequencesshowed highest similarity with MNSV (http://blast.ncbi.nlm.nih.gov/Blast.cgi). These partial RdRp sequences were submitted to GenBank obtaining number KU522434 for the watermelon and KU522435 for the melon isolate. They shared a nucleotide identity of 99.71 %. In addition, KU522434 (watermelon) shared 95.91 % identity with the previously reported MNSV-HM sequence from China (GenBank GU480022), while its identity with other reported MNSV sequences ranged from 70.20 % to 96.49 % (Table 1). Similar results were obtained with the corresponding sequence of the melon isolate (GenBank KU522435) (Table 1). DAS-ELISA was also successfully performed to confirm the presence of MNSV from diseased leaves. MNSV samples diluted by PBS buffer at 1: (20-26) were detected by DAS-ELISA using rabbit polyclonal antibody of MNSV (from NEOGEN, 1024) as capture antibody at 1/1000 dilution and detection antibody at 1/1000 dilution respectively. This is the first report of MNSV naturally infecting watermelon in China. This result suggests that MNSV has spread during past years in different hosts and regions in China. Quick and reliable detection on MNSV should be developed to avoid potential further losses of watermelon trade in China.

Viral diseases, the second most significant biotic stress, cause substantial yield loss and quality deterioration in sweet potato, and sweet potato latent virus (SPLV) is one of the dominant viral pathogens infecting sweet potato in China. To investigate SPLV-induced metabolic changes, untargeted LC-MS (liquid chromatography-mass spectrometry) was used on Nicotiana benthamiana inoculated with SPLV-infected sweet potato leaf sap. Principal component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA) confirmed distinct metabolite profiles between infected and mock control plants. In SPLV-infected plants, 626 metabolites exhibited significantly differential accumulation, with 429 upregulated and 197 downregulated. These differential metabolites were categorized into 14 distinct biochemical groups, and hierarchical clustering analysis intuitively visualized the expression patterns of the top 50 significantly different metabolites. Further, KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis revealed that 19 pathways were markedly perturbed upon SPLV inoculation. These results confirm SPLV’s significant effect on Nicotiana benthamiana metabolism, which helps elucidate SPLV-host interaction mechanisms and provides candidate metabolic targets for enhancing SPLV resistance in sweet potato.