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Candidatus Phytoplasma australiense

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Datasheet

Candidatus Phytoplasma australiense

Summary

  • Last modified
  • 31 October 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Natural Enemy
  • Preferred Scientific Name
  • Candidatus Phytoplasma australiense
  • Taxonomic Tree
  • Domain: Bacteria
  •   Phylum: Firmicutes
  •     Class: Mollicutes
  •       Order: Acholeplasmatales
  •         Family: Acholeplasmataceae
  • Summary of Invasiveness
  • Phytoplasmas are wall-less, phloem-limited unculturable bacteria that are naturally spread by sap-sucking insects. ‘Candidatus Phytoplasma australiense’, subgroup 16SrXII-B, is associated with a wide range of d...

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Pictures

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PictureTitleCaptionCopyright
Candidatus Phytoplasma australiense; symptoms on infected potato (Solanum tuberosum), showing the upward rolling and purpling of the leaves.
TitleSymptoms
CaptionCandidatus Phytoplasma australiense; symptoms on infected potato (Solanum tuberosum), showing the upward rolling and purpling of the leaves.
Copyright©Lia Liefting
Candidatus Phytoplasma australiense; symptoms on infected potato (Solanum tuberosum), showing the upward rolling and purpling of the leaves.
SymptomsCandidatus Phytoplasma australiense; symptoms on infected potato (Solanum tuberosum), showing the upward rolling and purpling of the leaves.©Lia Liefting
Candidatus Phytoplasma australiense; symptoms on strawberry infected with lethal yellows phytoplasma, showing purple-bronzing of older leaves.
TitleSymptoms
CaptionCandidatus Phytoplasma australiense; symptoms on strawberry infected with lethal yellows phytoplasma, showing purple-bronzing of older leaves.
Copyright©Mark Andersen
Candidatus Phytoplasma australiense; symptoms on strawberry infected with lethal yellows phytoplasma, showing purple-bronzing of older leaves.
SymptomsCandidatus Phytoplasma australiense; symptoms on strawberry infected with lethal yellows phytoplasma, showing purple-bronzing of older leaves.©Mark Andersen
Candidatus Phytoplasma australiense; Phormium yellow leaf symptoms on Phormium tenax (New Zealand flax), showing abnormal yellowing of leaves and stunted growth, which will  eventually result in plant death.
TitleSymptoms
CaptionCandidatus Phytoplasma australiense; Phormium yellow leaf symptoms on Phormium tenax (New Zealand flax), showing abnormal yellowing of leaves and stunted growth, which will eventually result in plant death.
Copyright©Mark Andersen
Candidatus Phytoplasma australiense; Phormium yellow leaf symptoms on Phormium tenax (New Zealand flax), showing abnormal yellowing of leaves and stunted growth, which will  eventually result in plant death.
SymptomsCandidatus Phytoplasma australiense; Phormium yellow leaf symptoms on Phormium tenax (New Zealand flax), showing abnormal yellowing of leaves and stunted growth, which will eventually result in plant death.©Mark Andersen

Identity

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Preferred Scientific Name

  • Candidatus Phytoplasma australiense R.E. Davis et al., 1997a

Other Scientific Names

  • Australian grapevine yellows phytoplasma
  • Australian lucerne yellows phytoplasma
  • Coprosma lethal decline phytoplasma
  • Cordyline sudden decline phytoplasma
  • cottonbush reduced yellow leaves phytoplasma
  • cottonbush witches' broom phytoplasma
  • Liquidambar yellows phytoplasma
  • papaya dieback phytoplasma
  • periwinkle phyllody phytoplasma
  • Phormium yellow leaf phytoplasma
  • pumpkin yellow leaf curl phytoplasma
  • strawberry green petal phytoplasma
  • strawberry lethal yellows phytoplasma

English acronym

  • AGY
  • AluY
  • CBRYL
  • CBWB
  • CLD
  • CSD
  • LaY
  • PDB
  • PYL
  • PYLC
  • SLY

EPPO code

  • PHYP08 (Phormium yellow leaf phytoplasma)

Summary of Invasiveness

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Phytoplasmas are wall-less, phloem-limited unculturable bacteria that are naturally spread by sap-sucking insects. ‘Candidatus Phytoplasma australiense’, subgroup 16SrXII-B, is associated with a wide range of diseases in Australia and New Zealand. Important commercial crop hosts of ‘Ca. Phytoplasma australiense’ include grapevine, papaya and strawberry. This phytoplasma is associated with rapid death of its papaya and cabbage tree hosts. In New Zealand, the insect vectors have been confirmed to be the endemic Cixiid planthoppers, Zeoliarus atkinsoni and Z. oppositus, while in Australia no vector has yet been determined, although the leafhopper, Orosius argentatus, has been implicated. Long distance spread of the phytoplasma is possible through infected vegetative propagating material. ‘Ca. Phytoplasma australiense’ is on the A1 list of regulated organisms for Canada and Bahrain, and is listed as a quarantine pest for the USA.

Taxonomic Tree

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  • Domain: Bacteria
  •     Phylum: Firmicutes
  •         Class: Mollicutes
  •             Order: Acholeplasmatales
  •                 Family: Acholeplasmataceae
  •                     Genus: Phytoplasma
  •                         Species: Candidatus Phytoplasma australiense

Notes on Taxonomy and Nomenclature

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Due to the difficulty in obtaining axenic cultures of phytoplasmas, they are informally designated as species of the ‘Candidatus Phytoplasma’ genus based on 16S rRNA gene sequences (IRPCM, 2004). In addition to species assignment, phytoplasmas are classified into groups and subgroups based on restriction fragment length polymorphism (RFLP) analysis of a 1.25 kb 16S rRNA gene segment (Lee et al., 1993; Lee et al., 1998).

Candidatus Phytoplasma australiense’ (Davis et al., 1997a) is a member of the Stolbur group (16SrXII), subgroup 16SrXII-B (Lee et al., 1998). Other species in the Stolbur group include ‘Ca. Phytoplasma japonicum’, ‘Ca. Phytoplasma fragariae’, ‘Ca. Phytoplasma solani’ and ‘Ca. Phytoplasma convolvuli’ (Zhao and Davis, 2016). The Stolbur group currently contains 11 different subgroups (XII-A to XII–K) with more subgroups expected to be added.

Sequence heterogeneity between the two copies of the 16S rRNA genes in phytoplasmas was first demonstrated in ‘Ca. Phytoplasma australiense’, Phormium yellow leaf isolate (Liefting et al., 1996). Since then, this sequence heterogeneity has been reported for many other phytoplasmas but has so far not affected their group classification.

A more detailed differentiation of ‘Ca. Phytoplasma australiense’ isolates by sequence analysis of the tuf gene revealed that there are three distinct tuf subgroups, designated tuf 1, tuf 2 and tuf 3 (Andersen et al., 2006). Subgroup tuf 1 is found in both Australia and New Zealand, tuf 2 isolates are found in New Zealand only and tuf 3 isolates are only found in Australia.

The complete genome sequence of two isolates from the tuf 1 subgroup of ‘Ca. Phytoplasma australiense’, have been determined, one isolate from Australia (Tran-Nguyen et al., 2008) and the other from New Zealand (Andersen et al., 2013). Comparative genomics of the two isolates revealed that although the housekeeping genes of the two isolates differ by less than 1% at the nucleotide level, the genomes differ in size by 80 kbp largely due to the number and size of potential mobile units (PMUs), which contributed to some changes in gene order (Andersen et al., 2013).

Description

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Phytoplasmas were originally referred to as mycoplasma-like organisms (MLOs) since morphologically and ultrastructurally they resemble the true mycoplasmas (Mycoplasma spp.), which belong to the class Mollicutes of the kingdom Prokaryotae. Ultrastructural studies of ‘Ca. Phytoplasma australiense’ have been performed by several researchers (Ushiyama et al., 1969; Magarey et al., 1988; Andersen et al., 2001Beever et al., 2004). The phytoplasmas were reported to be pleomorphic, comprising round, elongate, dumbbell and ring shaped elements, mostly 150 to 250 nm across but extending in length to 1000 nm and characterized by a peripheral zone of ribosome-like granules around a central nucleoplasmic net (Andersen et al., 2001). Although phytoplasmas cannot be morphologically or ultrastructurally distinguished from one another using electron or light microscopy (McCoy, 1979), it is a useful tool to confirm the presence of phytoplasmas detected by molecular methods.

Distribution

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Ca. Phytoplasma australiense’ is widespread in Australia, specifically in New South Wales, Queensland, South Australia, Victoria and Western Australia (Davis et al., 1997b; Streten and Gibb, 2005; Streten et al., 2005a). Australian grapevine yellows occurs only in Australia, where it is found in most viticultural regions with a particularly high incidence in the warmer inland districts of Sunraysia in New South Wales and Victoria, Riverina in New South Wales and the Riverland in South Australia (Magarey and Wachtel 1986; Bonfiglioli et al., 1996; Constable et al., 2004). In New Zealand, Phormium yellow leaf, Cordyline sudden decline and Coprosma lethal decline diseases are widespread in the North Island and northern half of the South Island (Boyce and Newhook, 1953; Andersen et al., 2001; Beever et al., 2004). The distribution of other diseases of ‘Ca. Phytoplasma australiense’ is limited to where the crop is grown, for example papaya dieback is mainly found in Queensland, the main papaya growing area in Australia.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Risk of Introduction

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Ca. Phytoplasma australiense’ can be introduced by the importation of infected viable plant parts, except seed.

Hosts/Species Affected

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In Australia, important commercial crop hosts for 'Ca. Phytoplasma australiense' include grapevine (AGY phytoplasma), papaya (PDB phytoplasma) and strawberry (green petal, little leaf or lethal yellows diseases) (Padovan et al., 1998). In Australia, other plant hosts of 'Ca. Phytoplasma australiense' include: Acaena novae-zelandiae (bidgee-widgee), Carica papaya (papaya), Catharanthus roseus (periwinkle), Cucurbita maxima (pumpkin), C. moschata (pumpkin), Einardia nutans (climbing saltbush), Enchylaena tomentosa (ruby saltbush), Euphorbia terracina (false caper), Exocarpus cupressiformis (cherry ballart), Gomphocarpus fruticosa (cottonbush, swan plant), Melilotus indicus (hexham scent), Jacksonia scoparia (winged broom pea), Liquidambar styraciflua (sweetgum), Paulownia fortunei (paulownia), Phaseolus vulgaris (bean), Helminthotheca (Picris) echiodes (bristly ox tongue), Maireana brevifolia (yanga bush), Medicago sativa (alfalfa), M. polymorpha, Trifolium spp. (clover) and Vigna radiata (mung bean) (Krake et al., 1999Schneider et al., 1999Davis et al., 2003; Pilkington et al., 2003Bayliss et al., 2005Streten et al., 2005bStreten and Gibb 2005Magarey et al., 2006Getachew et al., 2007; Habili et al., 2007Constable et al., 2016; Dermastia et al., 2017). Although bidgee-widgee, pumpkin, climbing saltbush, ruby saltbush, false caper, cherry ballart, swan plant, winged broom pea, bristly ox tongue, yanga bush, clover, cottonbush and M. polymorpha have been found near commercial crops of grapevine and strawberry, it is not known if they are incidental hosts or important in the epidemiology of diseases associated with ‘Ca. Phytoplasma australiense’.

In New Zealand, the common diseases associated with 'Ca. Phytoplasma australiense' are Phormium yellow leaf, strawberry lethal yellows, Cordyline sudden decline and Coprosma lethal decline. Since 2009, 'Ca. Phytoplasma australiense' has also been reported in Solanum tuberosum (potato), Solanum pseudocapsicum (Jerusalem cherry), Gomphocarpus fruticosa (swan plant), Apium graveolens (celery) and a Rubus hybrid (boysenberry) (Liefting et al., 2011).

Growth Stages

Top of page Flowering stage, Fruiting stage, Vegetative growing stage

Symptoms

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Symptoms associated with AGY phytoplasma infection of white grape varieties include irregular chlorosis or yellowing of leaves, which is seen as reddening in red varieties. The chlorotic patches on affected leaves may become necrotic. Leaves of affected shoots can overlap one another. Inflorescence/bunches may die. Berries of more developed bunches shrivel and fail to ripen. Stems of affected shoots often take on a bluish hue. Only a few shoots on a grapevine are usually affected and inflorescence and fruit are generally only affected on symptomatic shoots. Later in the season affected shoots tend to remain green and rubbery. In some situations phytoplasma infections may be associated with restricted growth of the grapevine but the nature of this association is not well understood. In Australia, infected grapes may not display symptoms every season (Constable et al., 2003, 2004)

Symptoms on pawpaw induced by PDB phytoplasma infection include: bunching of the inner crown leaves, rapid chlorosis of recently matured leaves, bending of the growing point, reduced latex flow, abnormal ripening or abscission of the fruit and death of the crown within one to four weeks of the first visible symptoms (White et al., 1997).

Other hosts in Australia may exhibit symptoms of leaf yellowing and curling in pumpkin, patchy chlorosis of the crown, dieback of apical and lateral branches and small leaves showing tip necrosis in sweet gum, witches'-broom, interveinal chlorosis and stunted growth in paulownia and little leaf and yellowing in bidgee-widgee.

Symptoms on New Zealand flax (Phormium spp.) induced by PYL phytoplasma infection include: abnormal yellowing of the leaves, stunted growth, increased root death, phloem necrosis and xylem gummosis of the rhizome vascular system (Liefting et al., 1996; Andersen et al., 1998a).

Symptoms on strawberry plants with little leaf and lethal yellows disease, induced by strains of 'Ca. Phytoplasma australiense' include: stunting, purpling of older leaves, reduced leaf size, yellowing of younger leaves and occasional plant death (Andersen et al., 1998b; Constable et al., 2016).

Symptoms on cabbage tree (Cordyline spp.) start as vascular discolouration and leaf yellowing followed by leaf desiccation and eventual plant collapse resulting in rapid death of affected plants within months of the first external symptoms becoming apparent (Andersen et al., 2001).

Symptoms on coprosma include leaf reddening or bronzing and dieback of shoots and branches (Beever et al., 2004).

Other hosts in New Zealand exhibit symptoms of upward rolling and purpling of the leaves (potato), witches'-broom, foliar yellowing and reduced leaf size (Jerusalum cherry), pink coloured foliage and leaf distortion (celery) and stunting of lateral branches and production of small chlorotic leaves (boysenberry) (Liefting et al., 2011).

List of Symptoms/Signs

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SignLife StagesType
Growing point / dieback
Inflorescence / blight; necrosis
Leaves / abnormal colours
Leaves / abnormal forms
Leaves / abnormal leaf fall
Leaves / necrotic areas
Stems / dieback
Stems / stunting or rosetting
Stems / witches broom

Biology and Ecology

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Phytoplasmas are limited to the phloem tissue of infected plants and are naturally spread by phloem feeding insects.

The development and reproductive strategies of ‘Ca. Phytoplasma australiense’ in its various hosts are not well understood. In Australia, grapevine symptom development is less likely to occur beyond January/February and the percentage of samples that test positive for phytoplasma using PCR techniques can decline in autumn (Gibb et al., 1999; Constable et al., 2003). Also, while it has been shown that there is a greater probability of the same grapevines displaying AGY symptoms from year to year, remission of symptoms can also occur and some grapevines look healthy the following season (Magarey and Wachtel, 1986; Constable et al., 2004).

These observations indicate the possibility that the titre of phytoplasma within the grapevine and perhaps the location and/or distribution of phytoplasmas within the plant may influence symptom expression. Environmental factors, such as temperature and its interaction with phytoplasma multiplication and survival, may also play a role in the expression of AGY symptoms, and the concept of heat curing phytoplasma infections in grapevine after several days of high temperature has been proposed (Magarey and Wachtel, 1986).

In Australia, ‘Ca. Phytoplasma australiense’ can overwinter in symptomless strawberry runners and symptoms occur early in the following growing season, soon after planting. New infections occurring early in the growing season on strawberry may result in symptom expression in the same growing season (F Constable, Department of Economic Development, Jobs, Transport and Resources, Victoria, Australia, personal communication, 2017). These observations could suggest that timing and titre are important in symptom expression in strawberry, with late, low-titre infections leading to the production of symptomless runners.

Means of Movement and Dispersal

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Vector Transmission

In New Zealand, the insect vectors of ‘Ca. Phytoplasma australiense’ are the Cixiid planthoppers, Zeoliarus atkinsoni and Z. oppositus (Liefting et al., 1997; Winks et al., 2014). Z. atkinsoni is monophagous and only feeds on Phormium spp. In contrast, Z. oppositus is polyphagous and has been reported from many plant species, especially those associated with low herbage, including sedges and grasses as well as Phormium spp. (Winks et al., 2014). Transmission trials determined that Z. oppositus is able to vector ‘Ca. Phytoplasma australiense’ to coprosma and cabbage tree (Winks et al., 2014). During these trials more than 60% Z. oppositus survived after three weeks on Cordyline australis and Coprosma spp., indicating that it must feed on these hosts. The ecology of Z. oppositus matches its vector status of ‘Ca. Phytoplasma australiense’. It is a very common species in natural and modified habitats throughout New Zealand in lowland to subalpine habitats and its distribution encompasses the known range of ‘Ca. Phytoplasma australiense’. The nymphal stages of Z. oppositus probably feed underground on plant rhizomes and roots, with adults present mostly over the summer months, although the detailed life cycle of most known species of Cixiidae has not been verified. The dramatic and highly visible outbreaks of Cordyline sudden decline in the 1980s could be the result of widespread plantings of C. robusta in the 1970s (Winks et al., 2014).

No insect vector has been determined for 'Ca. Phytoplasma australiense' in Australia. ‘Ca. Phytoplasma australiense’ has been detected in the common brown leafhopper, Orosius argentatus, using PCR in insects collected from vineyards and strawberry fields. It was shown that this leafhopper can occasionally acquire the phytoplasma from grapevine (Beanland et al., 1999) but its vector status has not been confirmed by transmission studies. In a survey of strawberry crops ‘Ca. Phytoplasma australiense’ was also detected in another leafhopper (Xestocephalus spp.), a planthopper (Thanatodictya spp.) and an undetermined species of the Tribe Gaetuliini, but no transmission studies have been done and their vector status is unknown (Constable et al., 2016).

Movement in Trade

Like other phytoplasmas, ‘Ca. Phytoplasma australiense’ may be introduced into new areas by importing infected vegetative propagating material.

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Leaves Yes Pest or symptoms usually visible to the naked eye
Roots Yes Pest or symptoms usually invisible
Seedlings/Micropropagated plants Yes Pest or symptoms usually invisible
Stems (above ground)/Shoots/Trunks/Branches Yes Pest or symptoms usually invisible
Plant parts not known to carry the pest in trade/transport
Flowers/Inflorescences/Cones/Calyx
Fruits (inc. pods)
Growing medium accompanying plants
True seeds (inc. grain)
Wood

Impact

Top of page AGY disease has been shown to be epidemic in the warmer irrigated districts of Sunraysia, New South Wales and Victoria, the Riverina, New South Wales and the Riverland, South Australia. In the years of highest incidence, severely affected vineyards were rendered uneconomical (Magarey and Wachtel, 1983). In the Riverland region, up to 13% yield losses have been observed in vineyards severely affected by the AGY disease and some severely diseased vines yielded up to 54% less than healthy vines (Magarey and Wachtel, 1983). In contrast, analysis of yield data from 1996-1998 indicated no significant difference in yield between asymptomatic and symptomatic Chardonnay vines expressing AGY symptoms at two study sites in the Sunraysia region. However, at a third study site, in the Sunraysia region, there was a moderately significant reduction in yield in 1996-1997 (43% yield loss, p=0.06) and 1997-1998 (44% yield loss, p=0.06). Another trial indicated a significant difference in yield between healthy vines and vines displaying both symptoms of AGY and restricted growth (54% yield loss, p=0.004) (Constable et al., 1998c).

PDB phytoplasma infections in pawpaw leading to pawpaw dieback can result in total destruction of plantations (Liu et al., 1996).

Phormium yellow leaf disease contributed to the demise of a natural fibre industry based on P. tenax in New Zealand (Boyce and Newhook, 1953).

Economic Impact

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AGY disease has been shown to be endemic in the warmer irrigated districts of Sunraysia, New South Wales and Victoria, the Riverina, New South Wales and the Riverland, South Australia. In the years of highest incidence, severely affected vineyards were rendered uneconomical (Magarey and Wachtel, 1983). In the Riverland region, up to 13% yield losses have been observed in vineyards severely affected by the AGY disease and some severely diseased vines yielded up to 54% less than healthy vines (Magarey and Wachtel, 1983). In contrast, analysis of yield data from 1996-1998 indicated no significant difference in yield between asymptomatic and symptomatic Chardonnay vines expressing AGY symptoms at two study sites in the Sunraysia region. However, at a third study site, in the Sunraysia region, there was a moderately significant reduction in yield in 1996-1997 (43% yield loss, p=0.06) and 1997-1998 (44% yield loss, p=0.06). Another trial indicated a significant difference in yield between healthy vines and vines displaying both symptoms of AGY and restricted growth (54% yield loss, p=0.004) (Constable et al., 1998).

PDB phytoplasma infections in papaya leading to papaya dieback can result in total destruction of plantations (Liu et al., 1996).

Phormium yellow leaf disease contributed to the demise of a natural fibre industry based on P. tenax in New Zealand (Boyce and Newhook, 1953).

Strawberry lethal yellows is a concern to strawberry-runner growers in the Katikati region of New Zealand, who may lose up to 10% of the plants in some plots (Andersen et al., 1998b). Similarly, strawberry little leaf and lethal yellows disease in Australia may result in a significant loss of plants, which affects production of runners and fruit.

Australian lucerne yellows, which is associated with both 'Ca. Phytoplasma australiense' and 'Ca. Phytoplasma aurantifolia', causes an estimated $7 million in annual loss to the Australian lucerne seed industries (Pilkington et al., 1999).

Social Impact

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The cabbage tree is one of New Zealand's most distinctive native trees and is widely used for planting in urban areas. During a survey of Cordyline sudden decline phytoplasma, about 11% of the trees under observation were lost each year in the northern half of the North Island, whereas less than 1% of trees in the southern North Island and northern half of the South Island died each year (Beever et al., 1996).

Risk and Impact Factors

Top of page Invasiveness
  • Invasive in its native range
  • Has a broad native range
  • Abundant in its native range
  • Is a habitat generalist
  • Reproduces asexually
  • Has high genetic variability
Impact outcomes
  • Host damage
  • Negatively impacts agriculture
  • Threat to/ loss of native species
Impact mechanisms
  • Pathogenic

Diagnosis

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Phytoplasmas are detected using polymerase chain reaction (PCR) techniques. The conventional nested-PCR using the P1 (Deng and Hiruki, 1991) and P7 primers (Schneider et al., 1995) followed by the R16F2n (Gundersen and Lee, 1996) and R16R2 (Lee et al., 1993) primers is the most commonly used assay for universal detection of all phytoplasmas. The resulting 1250 bp amplicon forms the basis for phytoplasma identification by sequence and/or RFLP analysis (Lee et al., 1993; Lee et al., 1998; IRPCM, 2004). Real-time PCR using TaqMan probes (Christensen et al., 2004; Hodgetts et al., 2009) is also becoming common for phytoplasma screening as it is more amenable to high throughput testing. These PCR assays have been used to detect and characterise ‘Ca. Phytoplasma australiense’.

PCR assays have been developed to specifically detect 'Ca. Phytoplasma australiense' (Gibb et al., 1999; Getachew et al., 2007) and also to distinguish between tuf gene clades 1 and 2 (Andersen et al., 2006).

Phytoplasmas, including 'Ca. Phytoplasma australiense' can be detected year round in Australian grapevines using PCR techniques (Constable et al., 2003). Additionally, phytoplasmas can be detected in roots, cordons, trunks and roots of Australian grapes. However, their distribution within grapevine tissues is not fully systemic (Constable et al., 2003). The detection of phytoplasmas by PCR is most reliable in January/February from AGY symptomatic shoots. From March onwards, the percentage of samples that tested positive for phytoplasma decline (Gibb et al., 1999; Constable et al., 2003).

Detection and Inspection

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In some cases, disease symptoms associated with 'Ca. Phytoplasma australiense' can be quite definite, such as cabbage tree in late stages of infection. In other hosts for reliable diagnosis, phytoplasma infection of plants showing symptoms need to be confirmed by PCR.
 

Similarities to Other Species/Conditions

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Mechanical disruption to the phloem of grapevine shoots can cause symptoms similar to those associated with AGY phytoplasma infection. It is important to inspect symptomatic shoots for damage to vascular tissue due to breakage, restrictions of the vascular tissue due to tendrils or string wrapping tightly around shoots, and damage to vascular tissue by boring insects.

Two other phytoplasmas distinct from 'Ca. Phytoplasma australiense' have been detected in grapevine displaying AGY symptoms (Gibb et al., 1999). One of these is the tomato big bud (TBB) phytoplasma from Australia, which is a member of the 16Srll (peanut witches broom) phytoplasma group, subgroup D (Lee et al., 1998). Additionally the TBB phytoplasma is considered to be a strain of the provisional taxon 'Ca. Phytoplasma australasiae' (White et al., 1998, not to be confused with 'Ca. Phytoplasma australiense'). The Buckland Valley grapevine yellows (BVGY) phytoplasma, which is the sole member of the 16SrXXIII phytoplasma group is only found in the Buckland Valley of Victoria, Australia (Constable et al., 2002; Gibb et al., 1999). The symptoms of AGY disease associated with each of these phytoplasmas resemble those associated with many grapevine infecting phytoplasmas in other countries.

In potato, the symptoms of 'Ca. Phytoplasma australiense' appear similar to that of 'Ca. Liberibacter solanacearum' (Liefting et al., 2009).

In Queensland, Australia, lethal yellows/little leaf symptoms of strawberry may also be associated with a rickettsia-like-organism (RLO). This RLO has not been detected in affected strawberries in other states of Australia or New Zealand (Streten et al., 2005bConstable et al., 2016).

As with other phytoplasma diseases, the symptoms can resemble damage caused by abiotic disorders such as chemical toxicity, nutrient deficiencies and temperature extremes.

Prevention and Control

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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Phytoplasma diseases are managed by the use of healthy planting material, removal of alternative weed hosts and chemical control of the insect vector. Specific control measures reported for diseases associated with ‘Ca. Phytoplasma australiense’ include:

Australian grapevine yellows – provision of material to nurseries from source blocks that have been inspected and found free from AGY symptoms, hot water treatment of 50°C for 30 minutes as the standard protocol for eliminating phytoplasmas from grapevine cuttings and planting material (Boidron and Grenan, 1992; Caudwell et al., 1993) and the management of irrigation and nutrition to improve or maintain vine health.

Papaya dieback – ratooning of diseased plants, which involves cutting the plants to a 0.75 m height as soon as external symptoms of the phytoplasma disease are observed (Guthrie et al., 1998).

Strawberry little leaf, green petal and lethal yellows – roguing of diseased plants (Andersen et al., 1998b).

References

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Andersen MT, Beever RE, Gilman AC, Liefting LW, Balmori E, Beck DL, Sutherland PW, Bryan GT, Gardner RC, Forster RLS, 1998. Detection of phormium yellow leaf phytoplasma in New Zealand flax (Phormium tenax) using nested PCRs. Plant Pathology, 47(2):188-196; 47 ref

Andersen MT, Longmore J, Liefting LW, Wood GA, Sutherland PW, Beck DL, Forster RLS, 1998. Phormium yellow leaf phytoplasma is associated with strawberry lethal yellows disease in New Zealand. Plant Disease, 82(6):606-609; 37 ref

Andersen, M. T., Beever, R. E., Sutherland, P. W., Forster, R. L. S., 2001. Association of "Candidatus Phytoplasma australiense" with sudden decline of cabbage tree in New Zealand. Plant Disease, 85(5), 462-469. doi: 10.1094/PDIS.2001.85.5.462

Andersen, M. T., Liefting, L. W., Havukkala, I., Beever, R. E., 2013. Comparison of the complete genome sequence of two closely related isolates of 'Candidatus Phytoplasma australiense' reveals genome plasticity. BMC Genomics, 14(529), (2 August 2013). http://www.biomedcentral.com/content/pdf/1471-2164-14-529.pdf

Andersen, M. T., Newcomb, R. D., Liefting, L. W., Beever, R. E., 2006. Phylogenetic analysis of "Candidatus Phytoplasma australiense" reveals distinct populations in New Zealand. Phytopathology, 96(8), 838-845. doi: 10.1094/PHYTO-96-0838

Bayliss, K. L., Saqib, M., Dell, B., Jones, M. G. K., Hardy, G. E. St J., 2005. First record of 'Candidatus Phytoplasma australiense' in Paulownia trees. Australasian Plant Pathology, 34(1), 123-124. doi: 10.1071/AP04089

Beanland L, Kelly M, Faggian R, MacFarlane J, Glenn D, 1999. In search of an insect vector of Australian grapevine yellows: species composition and abundance of potential vectors. The Australian Grapegrower and Winemaker, 430, 41-46.

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01/02/18 Updated by:

Lia Liefting, Virology, Plant Health & Environment Laboratory, Ministry for Primary Industries, Auckland, New Zealand

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