Melon necrotic spot virus

Melon necrotic spot virus (MNSV) is a virus that belongs to the genus Carmovirus of the family Tombusviridae. It has been observed in several countries of the Americas, Africa, Asia, and Europe. It is considered to be an endemic virus in greenhouses and field productions of Cucurbitaceae crops, including melon (Cucumis melo), cucumber (Cucumbis sativus), and watermelon (Citrullus lanatus). MNSV is mainly spread through infected soil, seedlings, insects, and by the root-inhabiting fungus vector Olpidium bornovanus. Symptoms vary between Curbitaceae crops, but generally consist of chlorosis, brown necrotic lesions, leaf wilt, fruit decay, and plant death. Management of the disease consists of preventing infection by rotating fields and crops, steam sterilization, and disposal of infected plants. Also, treated seeds with heat or chemicals are efficient in preventing infection. MNSV is important in melon plants as it causes vast economical damage worldwide reducing significant yields. Melons are one of the most important crops in the tropical and temperate areas of the world. MNSV has been found to have a very narrow host range, restricted to members of the family Cucurbitaceae. In particular, the hosts include watermelons (Citrullus lanatus), cucumbers (Cucumis sativus), and melons (Cucumis melo). On watermelon, MNSV produces chlorotic lesions on leaves, stems, and/or cotyledons, which turn into dark brown local lesions. These brown local lesions indicate necrosis occurring on the specific plant parts. Also, the fruit itself may become infected. The fruit may become misshaped with the melon flesh becoming discolored and brown ring rot becoming evident. The fruit can decay while on the plant in severe cases. In cucumbers, MNSV produces chlorotic lesions on leaves and cotyledons. In the chlorotic lesions, necrotic brown pinpoint lesions enlarge throughout the lesions, causing the leaf and/or cotyledons to wilt and die. Stem necrosis is generally absent. The cucumber fruit itself will not display lesions. In melons, such as rockmelon, muskmelon, and cantaloupe, MNSV produces necrotic lesions on the leaves and/or cotyledons. The roots will also exhibit necrotic lesions. The melon fruit decreases in size and displays necrotic spots on the rind as well. Overall, infection of the crop will produce small chlorotic spots on the leaves, stems, and/or cotyledons, which turn brown while enlarging in size. The necrotic lesions can cause death to the plant structure and plant as a whole. MNSV symptoms tend to be more severe at lower temperatures. Once a plant is infected with MNSV the infection persists until plant death. If no infection occurs, MNSV can survive in soil for several years. MNSV is seed-borne, soil-borne, and vector-borne. It spreads via two means: the soil fungus Olpidium bornovanus, which is soil-borne and moisture dependent, and the cucumber beetles: western spotted cucumber beetle (Diabrotica undecimpunctata undecimpunctata) and banded cucumber beetle (D. balteata). Since it is a virus, it is transmitted through vectors. Vectors are mediums with which any pathogens are transmitted. Through seed, infection occurs when the seeds are scattered in soil containing the virus-free fungus. This is known as “vector-mediated seed transmission”. MNSV which is carried on the seed is released into the soil.