Alfalfa; Grape; Papaya; Potato; Strawberry; Sweet gum

The cixiid planthoppers Zeoliarus (Oliarus) atkinsoni and Zeoliarus oppositus are the only known vectors of Ca. P. australiense.

Z. atkinsoni has only been demonstrated to transmit the phytoplamsa from Phormium to Phormium (Phormium yellows); while Z. oppositus is polyphagous and has been reported on many different plants.

To date, the insect vector responsible for the spread of Ca. P. australiense in Australia is not known. Zeoliarus spp. do not occur in Australia. Further research will be needed to characterize additional vectors. One suspected vector, the leafhopper Recilia hospes, has been reported from Hawaii.

Follow instructions in Phytoplasma Sample Screening and Confirmation

If you have taken the hands-on phytoplasma specific training at S&T Plant Pathogen Confirmatory Diagnostics Laboratory (PPCDL, formerly Beltsville lab), you can screen your own phytoplasma samples.
Note: You will still have to follow the protocol in the linked document for confirmations.

No specific signs are present.

There are a variety of symptoms, which vary according to host. Refer to the CAPS Pest Datasheet for images of symptomatic plants.

Alfalfa
Affected plants showed yellowing, witches" broom, and phloem discoloration.
Grape
Symptoms include irregular yellowing in white grape varieties (or reddening in red varieties), downward curling of leaves, followed by death of shoot apices and flowers, which shrivel and fall. Affected leaves fall prematurely, and diseased shoots can have a bluish hue, turn rubbery, and die. Often a single shoot or a few adjacent shoots on the same arm show symptoms.
Strawberry
Infected plants may become flatter to the ground than adjacent healthy plants and their foliage growth more open. Older leaves become purple-bronze in color, particularly toward the margin. Young leaves are smaller than normal, with shortened petioles and a conspicuous chlorosis (yellowing), initially occurring around the leaf margin, but later covering much of the leaf. Leaves on runners are small, curled, and twisted, light yellow in color, and form rosettes.
Papaya
Affected plants show a bunched appearance of inner crown leaves, with one or more leaves shriveling and dying. The larger crown leaves rapidly develop yellowing, then necrosis. The entire crown dies within 1 to 4 weeks, and the stem gradually dies back from the top.
Potato
Upward rolling and purpling of leaves was observed in plants that had "Ca. P. australiense" alone and in mixed infection with "Ca. Liberibacter solanacearum". The symptoms also appeared similar to those in zebra chip disorder, to which "Ca. L. solanacearum" is linked in New Zealand and the United States.

Surveys should take place when symptoms are most likely to be apparent, which will depend on the specific host plant being surveyed. Note that our best information is from Australia and New Zealand and surveys may need adjustment in the United States.

Alfalfa
In Australia, affected plants display symptoms in the spring and summer as the temperature rises and plants mature, with symptoms being rare in winter. More samples tested positive in the spring versus the summer.
Grape
Disease symptoms in Australia appear from flowering onwards (in late spring) and increase until harvest. However, in one vineyard of the "Shiraz" variety, symptoms did not appear until late summer and then increased in incidence until leaf fall with the fruit unaffected. The disease may not be persistently expressed in the same grapevine from season to season.
Clover
Symptomatic plants were observed in spring and fall in perennial pasture in Western Australia.
Papaya
Dieback occurs throughout the year, though there is usually a peak in symptom incidence during spring and fall in Australia.
Strawberry
Symptoms usually first appear in late spring and continue until harvest in fall in northern New Zealand.

Visually inspect host plants throughout the survey site for symptoms of the phytoplasma associated with the specific host. Collection efforts should be focused on plants with several of the known symptoms. Because these are destructive sampling methods, obtain permission from landowners or growers before attempting collection.

Survey for "Ca. P. australiense" in areas that grow alfalfa, cucurbits, grape, potato, papaya, strawberry, or sweet gum. Focus survey efforts in areas that grow multiple host crops at the same time or in crops with greatest acreage.

Inspect leaves, shoots, and fruit for symptoms associated with the phytoplasma. Symptomatic plants or even plant parts may occur singly or in patches. The distribution of infected plants within a survey area is likely related to vector movement. Magarey et al. (2006) showed that many vineyards exhibited relatively low numbers of affected vines often in randomly scattered clumps (suggesting long-distance dispersal from a source host), while other vineyards with a higher disease incidence exhibited gradients in disease incidence across the vineyard (suggesting proximal location of a source host plant or plants).

Collect samples of plant tissues that have symptoms of "Ca. P. australiense" infection. Collect 3-5 symptomatic leaves, including the petioles, from each symptomatic plant. If possible, take pictures of the symptomatic parts of the plant. Follow all proper sanitation precautions to avoid spreading plant diseases. Use sterilized knives/cutters and clean aseptically between samples and prior to use at the next survey site. Place the collected leaves from each symptomatic plant into separate plastic bags and seal without any extra moisture. Keep samples cool but do not freeze the plant material.

Note that phytoplasma concentrations can be unevenly distributed within the plant; therefore, collecting symptomatic tissue is particularly important, and obtaining a negative test result may not definitively exclude the phytoplasma as a causal agent.  

The approved diagnostic method is molecular identification. Follow instructions in 2023 Phytoplasma Sample Screening and Confirmation for CAPS and PPA 7721.
If you have taken the hands-on phytoplasma specific training at S&T Plant Pathogen Confirmatory Diagnostics Laboratory (PPCDL), you can screen your own phytoplasma samples.
Note: You will still have to follow the protocol in the linked document for confirmations.

iPhyClassifier: an interactive online tool that performs sequence similarity analysis, simulates laboratory restriction enzyme digestions and subsequent gel electrophoresis and generates virtual restriction fragment length polymorphism (RFLP) profiles. Based on calculated RFLP pattern similarity coefficients and overall sequence similarity scores, iPhyClassifier makes instant suggestions on tentative phytoplasma 16Sr group/subgroup classification status and Candidatus Phytoplasma species assignment (Zhao et al., 2009). This tool can be used for preliminary identification of "Ca. P. australiense"; however, it has not been evaluated by the S&T PPCDL and its practical functionality is undetermined.

Other phytoplasmas may cause similar symptoms.
In the United States, North American grapevine yellows (NAGY) disease occurs with the associated phytoplasmas Virginia grapevine yellows SrI-A and "Ca. P. pruni"-related strains NAGYIII. Symptoms of NAGY are very similar to those caused by "Ca. P. australiense". Molecular techniques are necessary to distinguish between these similar diseases.