Phagic

Viroids: The Viroids were discovered by Diener in 1971. The Viroids are infectious RNA particles. The capsid protective covering is absent. The molecular weight of viroids is in the range of 115,00 – 130,000 daltons. It contains circular RNA particles and is the smallest pathogens known. The viroids cause diseases in plants i.e they are pathogenic to plants only. E,g PSTD – potato spindle tuber disease, Citrus exocortis, Cucumber pale yellow.