Melon yellow spot virus in watermelon: a first record from Taiwan

During April 2007, systemic necrotic spots were observed on melon ( Cucumis melo ) grown in plastic greenhouses in Haimen city of Jiangsu Province, China. By mid May disease rates in different plastic houses ranged from 19 to 100% with symptoms characteristic of Melon necrotic spot virus (MNSV). These symptoms included many necrotic spots on the young leaves followed by coalescence of spots to form larger irregular lesions on older leaves. Necrotic stripes appeared on stems, and the infected leaves also became curled and wilted. Sap extracts in 0·01 M phosphate buffer, pH 7·0, from diseased plants were mechanically inoculated to melon, watermelon ( Citrullus lanatus ) and cucumber ( Cucumis sativus ). Melon, watermelon and cucumber all showed local necrotic spots on cotyledons 3 to 5 days post inoculation (d.p.i.) in the greenhouse and 6 d.p.i. under 20 ° C in a growth chamber, but systemic necrotic spots were observed only on melon plants, which began to appear 6 to 7 d.p.i. in the greenhouse and 9–14 d.p.i. at 20 ° C in a growth chamber. For further confirmation of the causal agent, primers MNSV-CP-5 ′ (GTGAAGCTTAARCAGGC) and MNSV-CP-3 ′ (ACRTARAGATCACCRTGGGC) were synthesized (Yakoubi et al ., 2008) to amplify a 710 bp region of the MNSV coat protein gene. The expected PCR product was amplified from Trizol extracted total RNA from virus infected fresh leaves, but no PCR products were amplified from healthy plant total RNA. The alignment of a 673 bp nucleotide sequence, which excluded the primer sequences (GenBank EU016217), showed 93 and 92% identity to MNSV isolates from Spain (GenBank DQ339157), and the Netherlands (GenBank M29671), respectively. MNSV has been previously reported in Japan, the Netherlands, UK, USA (Hibi & Furuki, 1985), Greece (Avgelis, 1985), Korea (Choi et al ., 2003), Spain (Diaz et al ., 2003) and other countries (e.g. Yakoubi et al ., 2008), but this is first report of MNSV in China.