Plant pathogenic phytoplasmas found in grasses in northern Australia have t
he 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 d
etermined. Sugarcane with and without symptoms of yellow leaf syndrome was
included in the surveys. Molecular methods were used to detect and characte
rize phytoplasmas in grass species exhibiting symptoms typical of phytoplas
ma disease. Sugarcane samples were from the Ord River Irrigation Area, West
ern Australia, and Samford, Queensland. Samples of other grasses were from
Wyndham, Kununurra and Broome, Western Australia, and Darwin, Northern Terr
itory. Our survey identified four new phytoplasma host species and confirme
d four known previously. Counting phytoplasmas, phytoplasma variants, and m
ixtures of phytoplasmas and variants, these eight host species had 33 diffe
rent infections. Two phytoplasmas were new, cenchrus bunchy shoot which is
related to Candidatus phytoplasma australiense, and sorghum bunchy shoot wh
ich is not closely related to any described phytoplasma. Twenty-five phytop
lasma isolates were detected in sugarcane. Of these, tomato big bud phytopl
asma was the most common. In most cases no clear association between phytop
lasmas and symptoms could be determined. None of the phytoplasmas in Austra
lian sugarcane, but two in other grasses, were closely related to phytoplas
mas associated with white leaf and grassy shoot diseases in Asian sugarcane
. This study demonstrates that diversity of phytoplasmas and grass host spe
cies in northern Australia is greater than previously thought, and that sym
ptoms alone are not always reliable indicators of phytoplasma presence or a
bsence. It provides the groundwork to improve future field surveys, and for
initiation of transmission trials to determine whether insect vectors capa
ble of transmitting phytoplasmas from native grasses to sugarcane are prese
nt in the region.