Symptoms of Apricots with Phytoplasma
Phytoplasmas fall into the 16SrX-B subgroup of European stone fruit yellows, commonly referred to as ESFY. Symptoms of ESFY vary depending upon the species, cultivar, rootstock, and environmental factors. In fact, some hosts may be infected but show no signs of the disease. Apricot yellows symptoms are often accompanied by leaf roll followed by leaf reddening, reduction of dormancy (leaving the tree at risk of frost damage), progressive necrosis, decline, and eventual death. ESFY afflicts blossoms and shoots in the winter, leading to a reduction or lack in fruit production along with chlorosis (yellowing) of the leaves during the growing season. Early breaks in dormancy leave the tree open to frost damage. At first, only a few branches may be afflicted but, as the disease progresses, the entire tree may become infected. Infection leads to shorter shoots with small, deformed leaves that may drop prematurely. Leaves have a paper-like appearance, yet remain on the tree. Infected shoots may die back and developing fruit is small, shrunken, and tasteless and may fall prematurely, resulting in a decreased yield.
Treating Stone Fruit Yellows in Apricots
The apricot phytoplasma is usually transferred to the host via insect vectors, primarily the psyllid Cacopsylla pruni. It has also been shown to be transferred through chip-bud grafting as well as in-vitro grafting. Unfortunately, there is no current chemical control measure for stone fruit yellows of apricots. The incidence of ESFY has, however, been shown to be reduced when great care is given to other control measures such as the use of disease free planting materials, insect vector control, removal of disease trees, and overall sanitary orchard management. At this juncture, scientists are still studying and struggling to understand this phytoplasma in order to ascertain a viable control method. The most promising of which would be the development of a resistant cultivar.
