Pear decline

Pear decline is a severe plant disease caused by the phytoplasma Candidatus Phytoplasma pyri. This pathogen invades the phloem of the tree, obstructing the transport of carbohydrates and essential nutrients, which ultimately leads to the collapse of the root system and the decline of the tree's health.

The disease primarily affects the European pear (Pyrus communis). Trees grafted onto specific quince rootstocks are particularly susceptible due to graft incompatibility, which facilitates the rapid colonization of the phytoplasma and exacerbates the necrotic symptoms in the graft union.

The symptoms are categorized into quick decline and slow decline. Quick decline manifests as sudden wilting and death of the entire tree, often occurring shortly after the fruit set. Slow decline is characterized by stunted growth, small chlorotic or reddish leaves, sparse foliage, and the gradual dieback of branches and twigs over several seasons.

The transmission of the pathogen is mediated by insect vectors, primarily pear psyllids (Cacopsylla pyri and related species). These insects acquire the phytoplasma while feeding on the phloem of infected trees and transmit it during subsequent feedings on healthy pear trees, allowing the disease to spread rapidly through an orchard.

Management of the disease relies heavily on prevention, as there is no chemical cure for infected trees. Growers must use certified virus-free rootstocks and scions, maintain a rigorous spray program to control psyllid populations, and remove and destroy any trees showing advanced symptoms of decline to protect the remaining orchard.