The plant pathogen Rhodococcus fascians. History, disease symptomatology, host range, pathogenesis and plant-pathogen interaction

Since 1927, outbreaks of the leafy gall disease caused by Rhodococcus fascians on annual and perennial herbaceous plants have put the ornamental plant industry at risk. More recently, Pistachio Bushy top syndrome (PBTS), a serious disease emerging in the Western United States, has been declared as a natural disaster by the U.S. Department of Agriculture. Recent developments indicate that the taxonomic position of R. fascians should be re-evaluated and circumscribed from other members of the genus. Due to the broad host range of this bacterium, economically important crops are in a vulnerable position especially with new members within the genus becoming able to interact synergistically with R. fascians to cause symptom development. The virulence strategies employed by R. fascians and the involvement of cytokinins (CKs) in its pathogenicity have been the subject of much controversy in the last years. Additionally, the detection of virulent strains of R. fascians from symptomatic tissues has been problematic for many researchers. This review focuses on plant-pathogen interaction in context with more recent findings on the association of CKs in virulence of R. fascians. Current knowledge on the worldwide distribution of the pathogen, a historical recap of its discovery and the economic impact of the disease caused by R. fascians are also described here.