植原体(学名：phytoplasma)是寄生于植物韧皮部的一类无细胞壁的原核致病菌。

Phytoplasmas are specialised bacteria that are obligate parasites of plant phloem tissue and transmitting insects (vectors). They were discovered by scientists in 1967 and were named mycoplasma-like organisms or MLOs. They cannot be cultured in vitro in cell-free media. They are characterised by their lack of a cell wall, a pleiomorphic or filamentous shape, normally with a diameter less than 1 μm, and their very small genomes.