Structure and Cultural History of a Mycetozoan Found in Tobacco Plants with Mosaic-Like Symptoms

Abstract

Stained sections of tobacco leaves with mosaic show an intracellular mycetozoan, Plasmodiophora tabacai. Invaded cells become necrotic and adjoining ones hyper-plastic. Plasmodia may be found in all diseased tissues except bast fibers and xylem, but not in healthy tissues. They have been cultured in sterilized water and Knop''s solution from naturally and experimentally infected plants after washing in HgCl2 (11000) for 1-3 min.; healthy plants treated in the same way gave negative results. Summarizing the life history: (1) thick walled spores germinate to form (2) the limax type of amoebulae which grow, divide, and may become uniflagellates. Flagellates may also be formed by the union of 2 gametes, produced from chromidia discharged by the nuclei of old amoebulae of the limax type. Either amoebulae or flagellates may form (3) cysts which on germination give rise to (4) a 2nd generation of amoebulae of different type, which by fusion give rise to (5) plasmodia. From the plasmodium, (6) free spores are formed in rows. Within each free spore 3-16 thick-walled spores are formed after its nucleus has discharged chromidia.