Tomato big bud, legume little leaf, and lucerne witches' broom: three diseases associated with different mycoplasma-like organisms in Australia

Abstract

The pathogens (presumed to be mycoplasma-like organisms) causing tomato big bud, legume little leaf, and a 'mild' form of lucerne witches' broom disease could be distinguished by differential symptomatology and incubation periods in tomato (Lycopersicon esculentum) and Datura stramonium. They were regarded as reference 'type strains' of the Australian yellows disease agents. Incubation periods of the tomato big bud and legume little leaf agents in the leafhopper vector Orosius argentatus were similar, but the pathogen causing mild lucerne witches' broom was not transmissible by this insect.

Six species of plants with yellows disease symptoms (shoot proliferation, small leaves, chlorosis, virescence) were collected from northern and southern Queensland. The pathogens were transmitted by O. argentatus to D. stramonium. From symptoms produced in this host, the various isolates were characterized as either the original big bud or little leaf reference strains. An isolate causing 'severe' lucerne witches' broom could not be distinguished from the legume little leaf type strain.