Phytoplasmas were found in 33 plant species that were not described as host plants in an earlier Australian survey. Plants displayed characteristic symptoms of little leaf, proliferation, and floral abnormalities. Restriction fragment length polymorphism analysis revealed 13 different restriction patterns. The majority of phytoplasmas showed a restriction pattern identical to that of either the tomato big bud (TBB) or sweet potato little leaf V4 (SPLL-V4) phytoplasma. Phytoplasmas from 6 plant species showed a restriction pattern similar to that of the pigeonpea little leaf (PLL) phytoplasma. One phytoplasma from garden bean displayed a restriction pattern identical to that found in papaya dieback and Australian grapevine yellows (AGY) phytoplasmas. Seven new restriction fragment patterns have been detected and sequence analysis of the 16S/23S spacer region revealed that 3 of these phytoplasmas are related to the faba bean phyllody (FBP) group. The spacer region of a graminaceous phytoplasma was most similar to phytoplasmas from the sugarcane white leaf group. Another graminaceous phytoplasma was identical to a phytoplasma from Indonesia. The spacer region of a phytoplasma from poinsettia (PoiBI) was identical to the western X-disease phytoplasma from North America and Europe. The spacer region of a phytoplasma in stylosanthes contained no tRNAIle. Full-length 16S rRNA gene sequences from selected new phytoplasmas were determined to corroborate results obtained from the spacer region analyses. Three of these phytoplasmas (galactia little leaf, vigna little leaf, and stylosanthes little leaf) are, along with the PoiBI phytoplasma and the graminaceous phytoplasmas, members of phytoplasma groups that have not been reported before 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.

Plant pathogenic phytoplasmas found in grasses in northern Australia have the potential to adversely affect sugarcane production. To begin assessment of this threat, the number of grass species with phytoplasmas, the identity of those phytoplasmas, and their relationship with disease symptoms were determined. Sugarcane with and without symptoms of yellow leaf syndrome was included in the surveys. Molecular methods were used to detect and characterize phytoplasmas in grass species exhibiting symptoms typical of phytoplasma disease. Sugarcane samples were from the Ord River Irrigation Area, Western Australia, and Samford, Queensland. Samples of other grasses were from Wyndham, Kununurra and Broome, Western Australia, and Darwin, Northern Territory. Our survey identified four new phytoplasma host species and confirmed four known previously. Counting phytoplasmas, phytoplasma variants, and mixtures of phytoplasmas and variants, these eight host species had 33 different infections. Two phytoplasmas were new, cenchrus bunchy shoot which is related to Candidatus phytoplasma australiense, and sorghum bunchy shoot which is not closely related to any described phytoplasma. Twenty‐five phytoplasma isolates were detected in sugarcane. Of these, tomato big bud phytoplasma was the most common. In most cases no clear association between phytoplasmas and symptoms could be determined. None of the phytoplasmas in Australian sugarcane, but two in other grasses, were closely related to phytoplasmas associated with white leaf and grassy shoot diseases in Asian sugarcane. This study demonstrates that diversity of phytoplasmas and grass host species in northern Australia is greater than previously thought, and that symptoms alone are not always reliable indicators of phytoplasma presence or absence. It provides the groundwork to improve future field surveys, and for initiation of transmission trials to determine whether insect vectors capable of transmitting phytoplasmas from native grasses to sugarcane are present in the region.

Forty-nine pear tree samples collected in Victoria, most of them showing decline symptoms, were tested by polymerase chain reaction (PCR) analysis to detect phytoplasmas. Two universal phytoplasma-specific primer pairs, fP1/rP7 and fU5/rU3, were tested, but only fU5/rU3 amplified the phytoplasma DNA adequately. Nested PCR with universal and group-specific primers, however, proved more effective. Thirty pear trees reacted positively in a nested PCR assay. Restriction fragment length polymorphism (RFLP) analysis with the restriction enzymes MseI and AluI of the PCR fragment amplified with the primer pair fU5/rU3 revealed patterns identical to those from the sweet potato little leaf phytoplasma. This is the first report of a phytoplasma in pear in Australia.

Stylosanthes sp. exhibiting characteristic symptoms such as little leaf, witches’ broom and floral abnormalities were collected from north Queensland and the Northern Territory, Australia. Previous studies have shown that sweet potato little leaf V4 (SPLL‐V4), tomato big bud (TBB), stylosanthes little leaf (StLL) and pigeon pea little leaf (PLL) phytoplasmas are associated with this disease. The detection of an additional phytoplasma type, vigna little leaf (ViLL) is reported herein. The range and severity of symptoms expressed by affected plants is highly variable and is not associated with a particular phytoplasma type. Similarly, host plants infected with a complex of two phytoplasmas did not have unique or more severe symptoms. Of the phytoplasmas associated with stylosanthes little leaf disease, StLL is unique because it lacks the tRNAIle gene which is normally situated in the 16S‐23S rRNA intergenic spacer region. This phytoplasma was shown to have a second operon containing the expected tRNAIle gene in all StLL samples examined. Sequence analysis suggests that the two 16S rRNA genes amplified by polymerase chain reaction from StLL samples originate from the same phytoplasma. This the first report of a phytoplasma having ribosomal operons both with and without an intergenic tRNAIle gene.