Almond; Peach, Nectarine

Not known to transmit any human or animal pathogens.

Not known to vector any pathogens or other associated organisms.

Ca. P. phoenicium is vectored by insects and can also be transmitted by vegetative propagation (grafting, cuttings, bulbs, etc.) of infected plant tissues.

There are three confirmed plant hopper vectors of "Ca. P. phoenicium":
Asymmetrasca decedens (syn. Empoasca decedens )
Tachycixius cf cypricus
Tachycixius viperinus

These vectors are not reported to occur in the United States

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 the S&T Beltsville lab (PPCDL), 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.

In almond: Symptoms include early flowering, stunted growth, leaf rosetting (short, bunchy growth due to shortened internodes and reduction in leaf size), dieback, off-season growth, proliferation of slender shoots, witches"-broom, and smaller pale green leaves. Witches"-broom symptoms arise mainly from the trunk or roots but can also occur on branches. Fruits produced from infected trees are smaller and darker in color with shriveled seeds, and fruit yield on infected branches is greatly reduced.
Infection by this phytoplasma can be asymptomatic in almond hosts and some almond cultivars are more susceptible to "Ca. P. phoenicium" than others. The susceptibility of almond cultivars grown in the United States is unknown.

In peach/nectarine: Symptoms early in the growing season include premature flowering followed by the early development of buds. Symptoms later in the growing season include shoot proliferation, smaller leaves with a pale green color, abnormal flowers (phyllody), and, in rare cases, witches" broom. Most infected trees do not set any fruit, but some trees bear a limited number of deformed fruits.

In apricot: Symptoms include leaf yellowing, shortened internodes, inward leaf curl, scorched leaf margins, leaf rosetting, die back, and plant death. Symptoms typically first emerge on one branch or a section of branches before spreading, and affected branches produce no fruit or fruit abnormal in size, shape, and taste.

Generally, the best time to test for phytoplasmas is at the end of summer. In Lebanon, "Ca. P. phoenicium" concentrations in the phloem tissue of stems and roots remained high in all seasons except autumn. It is uncertain how different environmental conditions would affect "Ca. P. phoenicium" titer.

Surveyors should perform visual surveys. Inspect host plants for symptoms and sample symptomatic tissue.

Survey for shoot proliferation, witches" broom symptoms, early flowering, rosetting, abnormal flowers (phyllody), smaller light green leaves, leaf roll, die back, reduction in fruit yield, and appearance of deformed fruits.

Survey for "Ca. P. phoenicium" in almond, peach, nectarine and apricot orchards.

For most phytoplasma diseases, leaves with symptoms are optimal for diagnostic testing. It is important to sample tissue from different parts of the same tree, as phytoplasmas are often unevenly distributed. For "Ca. P. phoenicium", the highest concentrations are found in the phloem tissues of stems and roots, but the phytoplasma can also be detected in leaf petioles or midribs, or flower petals. EPPO recommends sampling stems or roots from at least three parts of the tree. Do not sample necrotic tissue and ensure that soil is washed off roots.

Follow instructions in 2023 Phytoplasma Sample Screening and Confirmation for CAPS and PPA 7721.

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 the S&T Beltsville lab (PPCDL), you can screen your own phytoplasma samples. Note: You will still have to follow the protocol in the linked document for confirmations.

Currently there is no protocol validated by the S&T Plant Pathogen Confirmatory Diagnostics Laboratory (PPCDL) for specific detection of "Ca. P. phoenicium". 2023 Phytoplasma Sample Screening and Confirmation for CAPS and PPA 7721 is the screening assay recommended by PPCDL.

Jawhari et al. developed a specific PCR and a quantitative real-time PCR (qPCR) that can detect "Ca. P. phoenicium" in host phloem tissue or in insect vectors (Jawhari et al., 2015), and Kaddoura et al. developed a multiplex PCR that can discern 16SrIX-B from the closely related 16SrIX-C (Kaddoura et al., 2024). These assays can be used for preliminary identification of "Ca. P. phoenicium"; however, they have not been evaluated by the S&T PPCDL and their practical functionality is undetermined.

"Candidatus Phytoplasma phoenicium" infection may be confused with infection of other phytoplasmas, such as "Ca. P. prunorum", "Ca. P. pruni", and "Ca. P. aurantifolia", which also infect stone fruit. Of the three, only "Ca. P. pruni" is present in the United States. Visible symptoms alone are insufficient to diagnose phytoplasma infection, and molecular confirmation is critical for accurate identification.