Citrus stubborn disease is a serious economic problem in California, in Southwestern United States, and in other arid citrus areas of the world. Knowledge of the disease has rapidly increased since 1969 when a mycoplasma-like organism was found by electron microscopy in thin sections of diseased leaves. In 1970, a mycoplasma, now named Spiroplasma citri, was cultured from diseased citrus tissue. Further research has revealed that two leafhoppers (see California Agriculture, November 1973) can transmit the stubborn disease organism. Cultured spiroplasma have been fed or injected into these insects and they, in turn, have transmitted stubborn to healthy citrus seedlings. More recently (see California Agriculture, February 1975), one of the insects, Scaphytopius nitridus, fed on diseased citrus trees was shown to transmit a severe disease to healthy Vinca rosea L., periwinkle plants, in controlled greenhouse experiments. This information prompted our investigating the possibility of natural spread of stubborn into periwinkle plants.

This research was supported in part by a grant from the California Citrus Advisory Board