2025/03/12 by Elizabeth J. Fichtner, Craig E. Kallsen, Bruce Lampinen +2 · 1 voice
Agricultural and Biological Sciences · Biochemistry, Genetics and Molecular Biology · Engineering · #Plant Surface Properties and Treatments #Plant and Fungal Interactions Research #Tree Root and Stability Studies
paper · doi:10.21273/hortsci18322-24
openalex publication_date 2025/03/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/11
Pistachio bushy top syndrome (PBTS) emerged as a new disease of pistachio in the United States in 2011. The disease, caused by two phytopathogenic Rhodococcus spp., affected clonally propagated ‘UCB-1’ pistachio rootstocks, causing a suite of symptoms including stunting, shortened internodes, swollen lateral buds, bushy growth, altered bark and root morphology, and stem galls. Symptoms developed within 1 year of planting; however, the long-term influence of PBTS on orchard productivity was unknown because conventionally trained pistachio orchards are typically first harvested after the sixth season. The goal of this project was to determine the phenotypic characteristics and productivity of PBTS-affected trees in the seventh and eighth seasons, as trees entered maturity. Symptomatic and asymptomatic trees in a PBTS-affected orchard were evaluated for bark morphology, tree size, suckering potential, yield, nut quality, photosynthetic rate, foliar chlorophyll content, foliar nutritional status, stem water potential, and bloom progression. PBTS-affected trees exhibited at least a 20% reduction in growth, more than three times more suckering, and a greater than 50% reduction in yield compared with asymptomatic trees. In addition, PBTS-affected trees exhibited greater levels of blank nuts than asymptomatic trees; however, percent edible yield was unaffected by disease status. Symptomatic trees exhibited greater variability in tree size parameters, suckering, and edible yield than asymptomatic trees. The heterogeneity of PBTS symptomatic trees undermined the value of planting clonal rootstocks, and the deleterious impact of the syndrome on both yield and nut quality demonstrates that affected trees should be rogued upon initial symptom development rather than managed to maturity.