Rubus stunt: a review of an important phytoplasma disease in Rubus spp.

Phytoplasmas are cell wall-less plant pathogenic bacteria that colonize the phloem of their host plants and can be transferred by plant sap-sucking hemipteran insects or by vegetative propagation. In Rubus species such as red raspberry (Rubus idaeus) and blackberry (Rubus subgenus Rubus), phytoplasmas cause a disease which is referred to as Rubus stunt. Disease symptoms of Rubus stunt include stunting, witches’ broom, small leaves, short internodes, enlarged sepals, phyllody, flower proliferation, and fruit malformations. Rubus stunt is widely spread geographically and has been reported to be present throughout Europe, the former Soviet Union, the USA, Pakistan, and Turkey. As the incubation period of Rubus stunt can be up to 1 year and Rubus plants are usually produced by vegetative propagation, there is a high risk of spreading this disease in planting material. In addition, Rubus stunt is commonly overlooked because disease symptoms are often inconspicuous. Therefore, Rubus stunt has a high economic importance in these high-input crops with large initial investments. Here, we review the current state of knowledge on the causative agents of Rubus stunt, their spread, and control measures.