CSP Labs Blog » Pistachio Bushy Top Syndrome

Pistachio Bushy Top Syndrome

June 3rd, 2015
Padma Sudarshana, Ph.D. - Senior Scientist/Account Manager

In the recent years, a large number of pistachio trees in California and Arizona orchards have exhibited symptoms such as shortened internodes, twisted roots, stem galls and bushy top. The abnormal growth symptoms were observed with pistachio rootstock, UCB-1 and known to affect 10% to 90% of the trees in an infected orchard (Stamler et al. 2014). A bacterial pathogen, Rhodococcus fascians was identified as the causal organism of the pistachio bushy top syndrome. The California Department of Food and Agriculture (CDFA) assigned a pest rating-C to the pathogen based on the knowledge that R. fascians infections could lower crop yield and result in serious recurring economic losses to the pistachio industry. R. fascians survives as an epiphyte on plant surfaces and favors moist conditions and moderate temperatures. The bacterial transmission occurs primarily through the use of contaminated plant material and can also spread through irrigation water (Chitambar, 2015). R. fascians has a broad host range and survives in soil in the presence of host tissue. The use of disease free plant materials for propagation can be an effective control strategy to limit pathogen spread.

CSP Labs has validated a PCR test for the detection of R. fascians. The instructions for sample submission and forms can be found here.


  1. Stamler, R. A., J. Kilcrease, R. J. Heerama, C. E. Kallsen, and J. J. Randall. 2014. Rhodococcus sp. associated with Pistachio Bushy Top Syndrome in California and Arizona. Plant Disease (accepted for publication).
  2. Chitambar, J. 2015. Rhodococcus fascians. CDFA’s Division of Plant Health’s Pest Ratings and Proposals.