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Poster: Diseases of Plants: New & Emerging Diseases


Soil survival potential of pistachio bushy top syndrome isolates of Rhodococccus spp.
E. FICHTNER (1), S. Dhaouadi (1), E. Molina (2), R. Stamler (2), J. Randall (2) (1) University of California Division of Agriculture and Natural Resources, U.S.A.; (2) New Mexico State University, U.S.A.

Over 35,000 acres of pistachio planted from 2011-2014 in California were affected by pistachio bushy top syndrome (PBTS), a disease caused by bacteria related to Rhodococcus corynebacteriodes (Rc) and Rhodococcus fascians (Rf). Because the survival potential of PBTS isolates in soil is unknown, growers are reluctant to replant pistachios in affected orchards. The goal of this work was to assess the longevity of Rc and Rf in field soils exposed to environmental conditions and in potting medium under greenhouse conditions. An in situ field study was established in a PBTS orchard with each isolate embedded on wooden sticks and buried at various depths. Another study utilized excavated field soils incubated outdoors to investigate the influence of soil type and moisture on survival. In a greenhouse study, potting medium was infested with Rf in the presence and absence of dried pistachio plant material. After three months, populations of Rf in potting medium remained similar to initial populations, regardless of incorporation of plant tissue. After one month, Rf populations increased in moist, non-saline field soil, but Rc was almost eliminated. Both isolates were inhibited by salinity and drying, but depth did not influence survival. The results suggest saprophytic competence of Rf, and a consequent concern for persistence of Rf in affected orchards and nurseries and illustrate the need for vigilance in sanitation from the nursery to the field.