New severe strains of <i>Melon necrotic spot virus</i> : symptomatology and sequencing

Abstract

New strains of Melon necrotic spot virus (MNSV), designated MNSV‐YS and MNSV‐KS, caused much more severe growth retardation on melon plants than MNSV‐NH, which was previously reported as the most severe strain of MNSV in Japan. MNSV‐YS spread much more quickly than MNSV‐NH in infected plants, and induced more severe growth retardation, even though the appearance of necrotic lesions on inoculated cotyledons was much slower. MNSV‐KS had properties intermediate between those of the other two strains. The results suggest that faster‐spreading strains can multiply more rapidly as a result of lower levels of activity in inducing necrotic lesions in melon plants. The complete sequences of MNSV‐YS and MNSV‐KS were determined, and an RT–PCR–RFLP method based on these sequences was successfully developed to detect and discriminate between the three strains.