Detection and differentiation of phytoplasmas in Australia

In a polymerase chain reaction (PCR) diagnostic test, phytoplasma (formerly known as plant-pathogenic mycoplasma-like organism or MLO) ribosomal DNA was detected in total DNA extracts prepared from 56 out of 63 plants collected from geographically diverse locations across Australia. The list of phytoplasma hosts consisted of 38 different species in 16 different families. Restriction site analysis of the PCR-amplified DNA accessions was used to divide the phytoplasmas into 2 groups. The majority of the tomato big bud group and sweet potato little leaf group phytoplasmas were closely related to a phytoplasma originally obtained from Crotalaria in Thailand, which is a member of the faba bean phyllody strain cluster. In contrast, phytoplasmas associated with Australian grapevine yellows and papaya dieback were most similar to members of the aster yellows strain cluster. Twelve phytoplasmas were compared by Southern blot hybridisation with DNA cloned from the sweet potato little leaf phytoplasma strain V4. The restriction fragment length polymorphism pattern of all phytoplasmas compared was identical except for 2 sweet potato little leaf phytoplasmas.