Two New Strains of Melon Necrotic Spot Virus

Abstract

Two different isolates of melon necrotic spot virus (MNSV), designated as MNSV-NK and MNSV-NH were isolated from infected melons in Nagasaki Prefecture. The host ranges of these isolates were restricted to the Cucurbitaceae and were similar to that of an isolate of MNSV from Shizuoka Prefecture (MNSV-S), but they produced a different type of local lesion on cotyledons of Cucumis melo L. The rates of systemic infection induced by MNSV-NK, MNSV-NH and MNSV-S in C. melo L. were 9.1%, 90.1% and 3.6%, respectively. MNSV-NK and MNSV-NH were designated as a new serotype N, because these viruses were serologically related but not identical to MNSV-S (serotype S) with double diffusion test in agar gel. All three isolates had a single coat protein with molecular weight of 41k dalton. MNSV-NK and MNSV-NH had two species of single-stranded RNAs (RNA1 and RNA2), while MNSV-S had three (RNA1, RNA2 and RNA3). Only RNA1 (MW 1.51×10⁶) of each isolate retained pathogenicity. The origin of other RNAs was unknown yet. From these pathogenccal, serological and physical properties, three isolates were designated as NK, NH and S strains of melon nectoric spot virus.