A new phytoplasma detected in the South Australian native perennial shrub, Allocasuarina muelleriana

Abstract

Allocasuarina muelleriana shrubs growing in natural sclerophyll roadside vegetation near Willalooka in the upper south-east of South Australia have a high incidence of a yellowing disorder in either all or part of the foliage, combined in some cases with a shortening and curling of the leaf-bearing stems. Samples from symptomatic and adjacent asymptomatic plants were tested for phytoplasmas by the polymerase chain reaction (PCR) assay. All but one asymptomatic plant were negative for phytoplasmas, whereas about half of the symptomatic plants were positive. Restriction fragment polymorphism analysis of PCR products indicated that the phytoplasma was related to the buckthorn witches'-broom (BWB) and apple proliferation (AP) groups of phytoplasmas, members of which have not been previously reported in Australia. Further evidence from the sequence of the 16S rRNA gene and the use of PCR primers specific to the AP and pear decline (PD) phytoplasmas confirmed the close relationship to the BWB and AP group phytoplasmas.

‘Candidatus Phytoplasma spartii’, ‘Candidatus Phytoplasma rhamni’ and ‘Candidatus Phytoplasma allocasuarinae’, respectively associated with spartium witches'-broom, buckthorn witches'-broom and allocasuarina yellows diseases

“…These sequence similarity values are lower than those reported previously by Gibb et al (2003), who examined only a 1152 bp 16S rDNA fragment. At the 16S-23S rDNA spacer region level, the AlloY agent differs from AP-fruit tree phytoplasmas in 11-15 % of nucleotide positions and from the SpaWB and BWB phytoplasmas in 17 and 18 % of nucleotide positions, respectively.…”

“…These findings are consistent with data obtained by putative restriction site analysis. RFLP analysis of a PCR-amplified 880 bp 16S rDNA fragment by using MseI revealed that the AlloY phytoplasma is indistinguishable from the AP and PD phytoplasmas (Gibb et al, 2003). However, when the same rDNA fragments were digested with HpaII, the AlloY phytoplasma proved to be different from both the AP and PD phytoplasmas.…”

“…SpaWB is known to occur in Italy and Spain (Marcone et al, 1996;Torres et al, 2002) and BWB disease is present in south-western Germany (Seemüller et al, 1994;Mäurer & Seemüller, 1996), whereas AlloY disease occurs in Australia (Gibb et al, 2003). The causal agents, the SpaWB, BWB and AlloY phytoplasmas, are distinct phytoplasmas that are phylogenetically related more closely to phytoplasmas of the apple proliferation (AP) group than to other phytoplasma subclades (Seemüller et al, 1994(Seemüller et al, , 1998a(Seemüller et al, , 2002Mäurer & Seemüller, 1996;Marcone et al, 1996;Lee et al, 1998;Gibb et al, 2003). In this paper, it is proposed to consider the SpaWB, BWB and AlloY phytoplasmas as novel 'Candidatus Phytoplasma' species.…”

“…In particular, the rDNA of the AlloY phytoplasma, for which a partial 16S rDNA sequence (GenBank accession no. AY135523) had been determined previously by Gibb et al (2003), was resequenced in order to obtain the full-length 16S rDNA and 16S-23S rDNA spacer region sequences. For this purpose, rDNA of the AlloY pathogen was amplified by PCR using the universal phytoplasma primer pairs P1/rU3 (Deng & Hiruki, 1991;Lorenz et al, 1995) and fU5/m23SR (Lorenz et al, 1995;Padovan et al, 1995).…”

“…Specific detection of SpaWB and AlloY phytoplasmas is possible by using the reverse primers rSP and rAllo1 (Marcone et al, 1996;Gibb et al, 2003). The rSP primer was designed from the 16S-23S rDNA spacer sequence of the SpaWB phytoplasma (Marcone et al, 1996).…”