DETECTION AND DIFFERENTIATION OF PHYTOPLASMAS IN AUSTRALIA

In a polymerase chain reaction (PCR) diagnostic test, phytoplasma (for merly known as plant-pathogenic mycoplasma-like organism or MLO) ribos omal DNA was detected in total DNA extracts prepared from 56 out of 63 plants collected from geographically diverse locations across Austral ia. 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 gro up phytoplasmas were closely related to a phytoplasma originally obtai ned from Crotalaria in Thailand, which is a member of the faba bean ph yllody strain cluster. In contrast, phytoplasmas associated with Austr alian grapevine yellows and papaya dieback were most similar to member s of the aster yellows strain cluster. Twelve phytoplasmas were compar ed by Southern blot hybridisation with DNA cloned from the sweet potat o little leaf phytoplasma strain V4. The restriction fragment length p olymorphism pattern of all phytoplasmas compared was identical except for 2 sweet potato little leaf phytoplasmas.