Survey Instruction Details:
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.
Symptoms:
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.