Apple

Psyllid vectors: Cacopsylla picta (=C. costalis), C. melanoneura.
Leafhopper vector: Fieberiella florii.

The best time to sample aboveground tissue is in late summer to early fall, because the phytoplasma population is highest at this time. At least five samples per plant need to be collected due to the low titer and erratic distribution of the pathogen in the phloem of the plant. Phytoplasmas are present in the roots of infected plants year around.

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.

Symptoms: (unevenly distributed on the plants)

Apple: Leaves of infected plants roll downward and become brittle. Leaves are finely and irregularly serrated and are smaller than normal. Leaves turn red in autumn in contrast to the yellow coloration of healthy plants. Summer leaves are chlorotic (yellow). Early defoliation may occur. A rosette of terminal leaves sometimes develops late in the season in place of normal dormant buds.

Stipules are abnormally enlarged while petioles are rather short (an important symptom in nursery surveys). Shoots develop prematurely from axillary buds and give rise to secondary shoots (witches" brooming). The angle between the secondary shoots and the main shoots is abnormally narrow. Leaf rosette may appear on the shoot ends or the shoot tips may die (an important symptom in nursery surveys). In some cases, flowers show numerous petals and the peduncles are abnormally long. They fail to set and may stay on the tree for a long period. Fruit are reduced in size with incomplete coloration and poor flavor.

Root weight is reduced; the fibrous root system of infected trees forms compact felt-like masses of short roots so that the larger ones are unable to develop.

Trunk circumference and crown diameter are reduced compared to healthy trees. Shoots are thin and the bark, which is sometimes fluted lengthwise, has a reddish-brown color. Necrotic areas appear on the bark and some branches may wither. Diseased trees may die but often recover if adequately fertilized.

Cherry: Symptoms of AP in cherry include wilting, dying, and floral and phloem necrosis.

Apricot: Symptoms of AP in apricot include stem necrosis and leaf wilting.

Plum: The primary symptom of AP in plum is late blooming.

Dahlia: Symptoms of AP in dahlia include bushy growth accompanied by shoot proliferation, narowed leaves, and flower bud deficiency.

Rose: Symptoms of AP in rose include dieback, witches" broom, bud proliferation, stunted growth, leaf and flower malformation, and shoot and flower proliferation.

Lily: Symptoms of AP in lily include leaf malformation and necrosis, flower bud abscission.

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.

Phylogenetically closely related to the European stone fruit and pear decline phytoplasmas.

Serological: ELISA is available. Loi et al. (2002) developed monoclonal antibodies against apple proliferation phytoplasma. Brzin et al. (2003) showed that the ELISA procedure was very sensitive and reliable compared to PCR.

Grafting on sensitive indicator plants: Not recommended (very time intensive - up to 2 years). Malus x dawsoniana is a very sensitive indicator.

Green et al. (1999) developed an "easy and efficient" DNA extraction method from woody plants for detection of phytoplasmas by PCR.

Molecular: A "universal" PCR assay has been developed that enables amplification of the 16S rRNA genes of phytoplasmas. Digestion of these PCR products with selected restriction enzymes provides a DNA fingerprint in the form of 16S rDNA fragment patterns that can be used to determine phytoplasma identity (Deng and Hiruki, 1991; Ahrens and Seemuller, 1992; Lee et al., 1993; Smart et al., 1996; Gibb et al., 1999).

Nested PCR: Nested PCR has been employed for the detection of phytoplasmas both in plants and psyllids using universal primers (Deng and Hiruki, 1991; Gundersen and Lee, 1996) and/or 16SrX phytoplasma group specific primer pairs (Lee et al., 1995; Lorenz et al., 1995).

Seemuller and Schneider (2004) offer a summary of the molecular studies conducted on Ca. P. mali, Ca. P. prunorum, and Ca. P. pyri.

Immunocapture PCR (IC-PCR): Rajan and Clark (1995), use immunocapture-PCR to detect apple proliferation in apple bark. They used rabbit polyclonal antibodies to capture the phytoplasma and then amplified with universal PCR primers.

Real-time PCR: Jarausch et al. (2004) developed a quantitative real-time PCR for apple proliferation phytoplasma in plants and insects from a nitroreductase gene sequence. Galetto et al. (2005) developed an apple proliferation specific real-time PCR assay from the same nitroreductase gene sequence. These authors also developed a universal assay for detection of phytoplasmas belonging to groups 16Sr-V, 16Sr-X, and 16Sr-XII.

Torres et al. (2005) developed a real-time PCR that will detect Ca. P. mali, Ca. P. prunorum, and Ca. P. pyri (three phytoplasmas in apple proliferation group of quarantine importance).

Baric and Dalla-Via (2004) developed a real-time PCR for apple proliferation phytoplasma in apple plant material. The assay also amplified a host gene from apple as an internal control.

Baric et al. (2006) compared real-time PCR with four conventional PCR assays. The real-time procedure had the highest sensitivity and specificity and was not susceptible to PCR inhibition. The one downfall was the high cost of the procedure.

Aldaghi et al. (2007) developed a real-time PCR protocol for Ca. Phytoplasma mali. This probe could distinguish a single mismatch between Ca. P. mali and Ca. P. prunorum, but late fluorescent curves were obtained from European stone fruit isolates.

Aldaghi et al. (2008) developed a new probe and adapted the original procedure to eliminate the late fluorescent curves.

This phytoplasma was previously known as Phytoplasma AP-MLO on CAPS pest lists.This pest was thought to have been found in Canada but this is now thought to be a misidentification.