Poster: Epidemiology: Pathogen Dispersal
Transmission of Rhodococcus spp. causing pistachio bushy top syndrome in California
E. FICHTNER (1), S. Dhaouadi (1), T. Kapaun (2), J. Cardwell (3) (1) University of California Division of Agriculture and Natural Resources, U.S.A.; (2) University of California Division of Agriculture and Natural Resources, U.S.A.; (3) Companion Animal C
Pistachio bushy top syndrome (PBTS) is a new pistachio disease caused by two Rhodococcus spp., highly related to Rhodococcus fascians (Rf) and Rhodococcus corynebacteriodes (Rc). Determination of potential modes of pathogen transmission is necessary for protection of replants and asymptomatic trees in orchards, as well as prevention of similar future epidemics. The objectives of this study were to assess the potential for PBTS isolates to be transmitted to healthy plants via naturally-infested soil at replant sites, using pruning tools, or by rodents. Clonal UCB-1 (Pistacia atlantica x Pistacia integerrima) plants were planted in naturally-infested soil; positive and negative control treatments were established by placing root-inoculated and uninoculated plants in steam-disinfested soil. Pruning transmission studies were conducted by cutting into symptomatic tissue in advance of cutting healthy plants; positive and negative control treatments were established by artificial infestation and flame sterilization of pruners, respectively. Mice trapped in the greenhouse were evaluated for internal and external populations of Rf and Rc. The results demonstrate that naturally infested soil and infested pruning tools may transmit the bacteria to healthy plants. Mice were also found to carry Rhodococcus sp. on fur and in their digestive tract. The results underscore the need for vigilant sanitation, both in the orchard and in nursery propagation systems.