Karen S. Gibb

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.

Detection and differentiation of phytoplasmas in Australia: an update

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.

The effect of colony isolation of the predacious ant, Oecophylla smaragdina (F.) (Hymenoptera: Formicidae), on protection of cashew plantations from insect pests

Fierce boundary fights between Oecophylla smaragdina colonies were previously identified as the major factor limiting ant populations and the efficiency of ants as biological control agents. In order to determine the feasibility and effect ofpreventing boundary fights between colonies, experiments with full-, semi- and no-isolation of existing antcolonies in cashew plantations were done in 1996 and 1997. In a related experiment, ant colonies were transplanted from native vegetation to a cashew orchard. Trees with ant colonies which were fully isolated from other colonies were significantly less damaged by the main insect pests and produced significantly higher yield than those with ant colonies which were partly isolated or were not isolated. That was because fighting events between fully isolated ant colonies were eliminated, and the populations of these colonies were high throughout the cashew flowering and fruiting period. Trees in which O. smaragdina colonies were transplanted suffered little damage b...

'Candidatus Phytoplasma australiense' is the phytoplasma associated with Australian grapevine yellows, papaya dieback and Phormium yellow leaf diseases

Sequence comparisons and phylogenetic analysis of the 16S rRNA genes and the 16S/23S spacer regions of the phytoplasmas associated with Australian grapevine yellows, papaya dieback and Phormium yellow leaf diseases revealed minimal nucleotide differences between them resulting in the formation of a monophyletic group. Therefore, along with Australian grapevine yellows, the phytoplasmas associated with Phormium yellow leaf and papaya dieback should also be considered as ‘Candidatus Phytoplasma australiense’.

Distribution of the green ant, Oecophylla smaragdina (F.) (Hymenoptera: Formicidae), in relation to native vegetation and the insect pests in cashew plantations in Australia

The effect of native vegetation on the distribution of the green ant, Oecophylla smaragdina, and the main insect pests in cashew, Anacardium occidentale, plantations in tropical northern Australia was studied by field surveys and by observations. O. smaragdina was an efficient predator and the most abundant ant species in cashew plantations. Infestations of the main insect pests in the trees lacking ant nests were significantly higher than in those with ant nests. Although O. smaragdina were abundant on a wider range of native tree species, they preferred Acacia aulacocarpa and Planchonia careya, and they also thrived on cashew trees after dispersing into cashew plantations. In cashew plantations, O. smaragdina preferentially colonized trees with thick canopies irrespective of tree height. Fierce fights between O. smaragdina colonies were a major factor responsible for changes in population sizes, colonization and distribution of O. smaragdina in cashew plantations. The availability of preferred native tr...

Microclimate and limits to photosynthesis in a diverse community of hypolithic cyanobacteria in northern Australia.

Hypolithic microbes, primarily cyanobacteria, inhabit the highly specialized microhabitats under translucent rocks in extreme environments. Here we report findings from hypolithic cyanobacteria found under three types of translucent rocks (quartz, prehnite, agate) in a semiarid region of tropical Australia. We investigated the photosynthetic responses of the cyanobacterial communities to light, temperature and moisture in the laboratory, and we measured the microclimatic variables of temperature and soil moisture under rocks in the field over an annual cycle. We also used molecular techniques to explore the diversity of hypolithic cyanobacteria in this community and their phylogenetic relationships within the context of hypolithic cyanobacteria from other continents. Based on the laboratory experiments, photosynthetic activity required a minimum soil moisture of 15% (by mass). Peak photosynthetic activity occurred between approximately 8 degrees C and 42 degrees C, though some photosynthesis occurred between -1 degrees C and 51 degrees C. Maximum photosynthesis rates also occurred at light levels of approximately 150-550 micromol m(-2) s(-1). We used the field microclimatic data in conjunction with these measurements of photosynthetic efficiency to estimate the amount of time the hypolithic cyanobacteria could be photosynthetically active in the field. Based on these data, we estimated that conditions were appropriate for photosynthetic activity for approximately 942 h (approximately 75 days) during the year. The hypolithic cyanobacteria community under quartz, prehnite and agate rocks was quite diverse both within and between rock types. We identified 115 operational taxonomic units (OTUs), with each rock hosting 8-24 OTUs. A third of the cyanobacteria OTUs from northern Australia grouped with Chroococcidiopsis, a genus that has been identified from hypolithic and endolithic communities from the Gobi, Mojave, Atacama and Antarctic deserts. Several OTUs identified from northern Australia have not been reported to be associated with hypolithic communities previously.

Chromosome mapping of the sweet potato little leaf phytoplasma reveals genome heterogeneity within the phytoplasmas

To further understand the genomic diversity and genetic architecture of phytoplasmas, a physical and genetic map of the sweet potato little leaf (SPLL) strain V4 phytoplasma chromosome was determined. PFGE was used to determine the size of the SPLL-V4 genome, which was estimated to be 622 kb. A physical map was prepared by two-dimensional reciprocal digestions using the restriction endonucleases BssHII, Smal, Eagl and I-Ceul. Sixteen cleavage sites were located on the map. Southern hybridizations of digested SPLL-V4 chromosomal DNA were done using random clones and PCR-amplified genes as probes. This confirmed fragment positions and located the two rRNA operons and the linked fus/tuf genes encoding elongation factors G and Tu, respectively, on the physical map. An inversion of one of the rRNA operons was observed from hybridization data. Sequence analysis of one of the random clones identified a gid gene encoding a glucose-inhibited division protein. Digestions of the tomato big bud (TBB) phytoplasma chromosome with the same four enzymes revealed genome heterogeneity when compared to the closely related SPLL-V4, and a preliminary chromosome size for the TBB phytoplasma of 662 kb was estimated. This mapping information has revealed that significant genome diversity exists within the phytoplasmas.

Phytoplasma diseases in sub-tropical and tropical Australia

Phytoplasmas are phloem-limited plant pathogens that have been identified in over 1000 plant species worldwide. Outbreaks of the phytoplasma-related disease, papaya dieback, has resulted in 10–100% crop losses in south-east Queensland and Western Australia. Strawberry lethal yellows and green petal disease outbreaks in Queensland have led to 10–50% of strawberry runners being destroyed. Lucerne yellows disease has been reported to cause an annual loss of AU

Multiple approaches to microbial source tracking in tropical northern Australia

7 million to the lucerne seed industry. Disease surveys in Australia have increased our understanding of phytoplasma diseases in Australia and these fastidious organisms have been detected in ≈70 native and introduced plant species. The majority of the Australian phytoplasmas are assigned to the 16SrII group, however, a member of the 16SrXII group is more commonly associated with economically important diseases in Australia such as strawberry lethal yellows, papaya dieback and grapevine yellows. These phytoplasma diseases have been diagnosed using PCR primers specific for their 16S rRNA gene. Screening hundreds of samples using PCR is time consuming and expensive so current and future studies are characterising an Australian phytoplasma genome and identifying suitable targets for the development of a more rapid diagnostic test for phytoplasmas. Australasian Plant Pathology Society 2006

Mitochondrial DNA supports the identification of two endangered river sharks (Glyphis glyphis and Glyphis garricki) across northern Australia

Microbial source tracking is an area of research in which multiple approaches are used to identify the sources of elevated bacterial concentrations in recreational lakes and beaches. At our study location in Darwin, northern Australia, water quality in the harbor is generally good, however dry‐season beach closures due to elevated Escherichia coli and enterococci counts are a cause for concern. The sources of these high bacteria counts are currently unknown. To address this, we sampled sewage outfalls, other potential inputs, such as urban rivers and drains, and surrounding beaches, and used genetic fingerprints from E. coli and enterococci communities, fecal markers and 454 pyrosequencing to track contamination sources. A sewage effluent outfall (Larrakeyah discharge) was a source of bacteria, including fecal bacteria that impacted nearby beaches. Two other treated effluent discharges did not appear to influence sites other than those directly adjacent. Several beaches contained fecal indicator bacteria that likely originated from urban rivers and creeks within the catchment. Generally, connectivity between the sites was observed within distinct geographical locations and it appeared that most of the bacterial contamination on Darwin beaches was confined to local sources.