Viroid and bacteroid plastids

Viroids are tiny units of ribonucleic acid (RNA) that infect cells and replicate themselves. Damage to cultivated crops and other plants has been reported, and orchids have not been found to be infected. The molecular weight of viroid is smaller than that of viruses, about 75000 to 120000 and 1 million to 10 million respectively.

Mycoplastids are simple organisms that lack formed nuclei and cell walls, but are surrounded by a three-tier strand. The so-called "cells" of mycoplastids are very small, only 175~250nm in diameter, and contain cytoplasm and nuclear-like lineages and ribosomes. It may be linear, spiral, ovoid or spherical. Insects are the main transmission vectors of plant mycoplast pathogens. It is known that more than 300 species of plants are infected by mycoplasts, which mainly cause chlorosis or yellowing atrophic diseases, with only a few cases of orchids. Tetracycline antibiotics have inhibitory effect on mycoplastids, but have no effect on viruses. (Chen Xinqi, Ji Zhanhe)