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High Temperatures Activate Local Viral Multiplication and Cell-to-Cell Movement of Melon necrotic spot virus but Restrict Expression of Systemic Symptoms

First author: The Yokohamaueki Co. Ltd., Minami, Yokohama 232-8587, Japan; second author: Southern Prefectual Horticulture Institute, Chiba Prefecture Agriculture Research Center, Tateyama, Chiba 294-0014, Japan; third, fifth, sixth, seventh, and eighth authors: National Agricultural Research Center, Tsukuba, Ibaraki 305-8666, Japan; and fourth author: National Agricultural Research Center for Kyushu Okinawa Region, Koshi, Kumamoto, 861-1192, Japan.

The infection of melon plants by Melon necrotic spot virus (MNSV) and the development of necrotic disease symptoms are a seasonal occurrence in Japan, which take place between winter and early summer, but not during mid-summer. In this paper we investigate the effect of three different temperatures (15, 20, and 25°C) on the local and systemic expression of MNSV in melon plants. Previously, the incidence of plants expressing systemic symptoms caused by MNSV and other viruses was found to be greater at temperatures less than 20°C. In this study, our temperature-shift experiments support previous studies that found the expression of systemic symptoms increases as temperature falls from 25 to 20°C and decreases as temperature rises from 20 to 25°C. However, MNSV replication in melon cells and local viral movement within leaves following the inoculation of melon protoplasts or cotyledons were more frequent at 25°C than at 15 or 20°C.

Additional keywords:global climate change, methyl bromide, Olpidium bornovanus, posttranscriptional gene silencing, soilborne disease, symptom development.