Almond; Peach, Nectarine

There are three confirmed plant hopper vectors of "Ca. P. phoenicium":
Asymmetrasca decedens (syn. Empoasca decedens ) (Abou-Jawdah et al., 2014).
Tachycixius cf cypricus (Tedeschi et al., 2015).
Tachycixius viperinus (Tedeschi et al., 2015).

These vectors are not reported to occur in the United States

Follow instructions in Phytoplasma Sample Screening and Confirmation

If you have taken the hands-on phytoplasma specific training at S&T 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.

In almond: Symptoms include early flowering, stunted growth, leaf rosetting (a disease symptom characterized by short, bunchy growth habit due to shortened internodes and reduction in leaf size), dieback, off-season growth, proliferation of slender shoots, witches"-broom, and smaller pale green leaves (Abou-Jawdah et al., 2002). Witches"-broom symptoms arise mainly from the trunk or roots (Abou-Jawdah et al., 2002). The phytoplasma has also been detected in symptomless almond hosts (Abou-Jawdah et al., 2002).

Some almond cultivars are more susceptible to "Ca. P. phoenicium" than other cultivars. In Lebanon, the Alwani and Awja cultivars are highly susceptible and developed severe symptoms, and the Kachabi cultivar is less severely affected (Verdin et al., 2003). The susceptibility of almond cultivars grown in the United States is not currently known.

In peach/nectarine: Symptoms early in the growing season include premature flowering followed by the early development of buds (Molino-Lova et al., 2011). Symptoms later in the growing season include: shoot proliferation, smaller leaves with a pale green color, abnormal flowers (phyllody), and witches"-broom symptoms in rare cases (Abou-Jawdah et al., 2010). Most infected trees do not set any fruit, but some trees bore a limited number of deformed fruits (Abou-Jawdah et al., 2010).

Follow instructions in Phytoplasma Sample Screening and Confirmation

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

"Candidatus Phytoplasma phoenicium" infection may be confused with infection of other phytoplasmas. For example, "Ca. P. prunorum" and "Ca. P. pruni" are two other phytoplasmas that infect stone fruit (Seemuller and Schneider, 2004; Davis et al., 2013), and "Ca. P. pruni" is present in the United States. Verdin et al., (2003) identified a closely related but distinct phytoplasma that infects almonds in Iran and was found to be in phytyoplasma group 16SrIX-C. This phytoplasma is tentatively named Khafr almond witches"-broom (KAlmWB) and is closely related to Knautia arvensis phyllody (KAP) phytoplasma (Salehi et al., 2006).

Bacterial spot (Xanthomonas arboricola pv. pruni) is a relatively new disease of almond in California. This disease also infects other stone fruit, including peach and cherry. Symptoms include leaf spotting, lesions, and cankers, however, which are not associated with "Ca. P. phoenicium" infection (UC-IPM, 2015).

"Candidatus Phytoplasma phoenicium" can be identified by nested PCR and RFLP analysis (Abou-Jawdah et al., 2002, 2014; Tedeschi et al., 2015) or sequencing of 16S rDNA (Verdin et al., 2003; Abou-Jawdah et al., 2014). Jawhari et al. (2015) also developed a specific PCR and a quantitative real-time PCR (qPCR) which can detect "Ca. P. phoenicium" in host phloem tissue or in insect vectors. Quaglino et al. (2015) published a draft genome sequence of "Ca. P. phoenicium".