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Plantwise Technical Factsheet

peach rosette phytoplasma (peach rosette phytoplasma)

Host plants / species affected
Prunus amygdalus
Prunus angustifolia (Mountain cherry tree)
Prunus armeniaca (apricot)
Prunus avium (sweet cherry)
Prunus cerasus (sour cherry)
Prunus domestica (plum)
Prunus persica (peach)
Prunus salicina (Japanese plum)
List of symptoms/signs
Fruit  -  abnormal shape
Fruit  -  premature drop
Fruit  -  reduced size
Growing point  -  dieback
Growing point  -  discoloration
Growing point  -  distortion
Leaves  -  abnormal colours
Leaves  -  abnormal forms
Leaves  -  abnormal leaf fall
Leaves  -  leaves rolled or folded
Leaves  -  necrotic areas
Leaves  -  yellowed or dead
Roots  -  reduced root system
Seeds  -  distortion
Stems  -  dieback
Stems  -  stunting or rosetting
Stems  -  witches broom
Whole plant  -  distortion; rosetting
Whole plant  -  dwarfing
Whole plant  -  early senescence
Whole plant  -  plant dead; dieback
Symptoms
The most characteristic symptom of diseased peach trees is the production of numerous multiple axillary buds and excessive numbers of shoots with extremely shortened internodes (Kunkel, 1936; McClintock et al., 1951; Kirkpatrick et al., 1975; KenKnight, 1976). This growth behaviour is mostly related to the death of the terminal bud. As the leaves are formed on this growth, they are normal in size but appressed into distinct dense rosettes. At the base of these rosettes are one or two abnormally long and straight leaves with inrolled margins. These outer leaves turn yellow and drop readily in early summer, leaving only tufts of younger leaves near tips of naked twigs. Very few adventitious shoots develop in the interior of the tree canopy. Affected trees produce only a few, small and misshapen fruits that drop prematurely. Severely affected trees usually die during the first year of infection. On Japanese plum, infected leaves develop chlorosis and often a reddish blush and rosette symptoms are less pronounced than on peach (Kirkpatrick, 1995). Affected plum trees may survive 2 to 3 years after the appearance of symptoms.

Prevention and control
Use of healthy plant material and removal of diseased peach trees are important measures for control of PR phytoplasma. In addition, wild plum appears to be an important endemic reservoir of the pathogen and should not be allowed to grow near commercial orchards.
Impact
Although sporadic outbreaks of the disease do occur, PR disease is of minor importance (Kirkpatrick, 1995).

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