Identification of the Causal Agent of Witches Broom on Blue Palo Verde, Dr. Ursula Schuch and Dr. Judith Brown
Witches broom disease of the blue palo verde has become a significant threat to producers in Arizona and to the sustainability of palo verde as a lucrative, drought tolerant, native tree for landscape use. Arizona nurseries have lost tens of thousands of dollars because broom-infested trees must be discarded. Many trees planted in public and private landscapes have been removed due to lost esthetic and functional value, and compromised tree structure.
This project will investigate the cause of palo verde broom by addressing several untested hypotheses, including possible causality due to palo verde gall mite feeding, and the involvement of plant viruses or fastidious bacteria. The proposed objectives are: (i) monitor mite dynamics seasonally in relation to symptom development/spread, (ii) conduct mite feeding studies from asymptomatic and symptomatic plants, and attempt ‘transmission’ to palo verde seedlings, and (iii) assess biomarker and genetic/genomic signatures in mites, and in newly emerged leaves from symptomatic and asymptomatic trees.
Jan 2017 update: Analysis is ongoing. Fruit and flowers from both healthy and affected tissue has been gathered and is being analyzed. Seeds from affected plants are being grown out to extract specific pathogen bi-products. Dr. Schuch gave an update on the progress at the Desert Horticulture Conference, June, 2016. Many more samples were taken in the summer of 2016. A NO-COST EXTENSION HAS BEEN GRANTED – Work will be completed by June 30, 2017. Deliverables include a talk at WCISA, presumably in 2018.