Mosaic disease

A disease in which dark green and light green or yellowish green areas appear in a mosaic pattern on the leaves of crops, especially new leaves. The pathogen is a virus, and when a plant is infected with a virus, abnormalities occur in the intracellular components of the infected cells, causing the chloroplasts to become smaller and less numerous, accumulate starch, become vacuolated, and the lamellar structure becomes disorganized and collapses. The abnormal parts of the cells become light green to yellowish green, resulting in mosaic symptoms, which is one of the characteristics of plant diseases caused by viruses, and cases in which mosaic symptoms are prominent are called mosaic diseases. In many cases, in addition to the mosaic symptoms, there are also atrophy symptoms, and the plant height becomes small. Mosaic diseases occur in many crops, and the damage is particularly severe in legumes, vegetables, and flowers. There are many types of pathogenic viruses, some of which infect many plants, such as the cucumber mosaic virus and the tobacco mosaic virus, while others, such as the legume mosaic virus, have a relatively narrow host range.

[Toshihiro Kajiwara]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

作物の葉、とくに新葉に濃緑色の部分と淡緑色あるいは黄緑色の部分がモザイク状に現れる病気。病原はウイルスで、植物がウイルスに侵されると、感染細胞では細胞内成分の異常がおこり、葉緑体の小形化、数の減少、デンプンの蓄積、空胞化、ラメラ構造が乱れ崩壊する。このような細胞の異常がおこった部分が淡緑色から黄緑色を呈するため、モザイク症状になるもので、ウイルスによる植物の病気の特徴の一つになっており、モザイク症状の顕著に現れるものをモザイク病と称している。多くの場合、モザイク症状のほかに萎縮(いしゅく)症状を伴い、草丈が小さくなる。モザイク病は多くの作物に発生し、とくにマメ類、野菜類、花類で被害が大きい。病原ウイルスの種類も多く、キュウリモザイクウイルス、タバコモザイクウイルスのように多くの植物を侵すものや、マメ類のモザイクウイルスのように比較的寄主範囲の狭いものもある。

［梶原敏宏］

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