A New Disease of Onion Caused by Mycoplasma-like organism in Japan

Abstract

A new disease of onion (Allium cepa) caused by mycoplasma-like organism (MLO) was found in Saga Prefecture. The typical symptoms of diseased onion leaves were yellowing and stunting with fasciculation. Hypertrophy of the diseased onion bulb was decreased while flower clusters of the bulb were teratoid. The diseased onion bulb during storage was sprouted earlier than healthy one. In ultrathin sections of the diseased onion, MLO was observed in the sieve tubes of diseased leaves. In transmission tests with 5 species of wild planthopper and leafhoppers, only Macrosteles orientalis could inoculate and transmit the MLO to onion seedlings. The inoculated seedlings expressed the typical symptoms 20-28 days after transmission tests and MLO was detected in the sieve tubes of the onion leaves. The transmission rate of MLO by naturally infested M. orientalis ranged from 3.3 to 33%. The results indicate that the causal agent of this disease seemed to be MLO, and this disease was proposed to name “Onion yellows”.