Karla Huerta-Acosta, C.H.D Sagawa, A.M. Dandekar, and M. Andrew Walker*
*UC Davis, Viticulture and Enology, Davis, CA 95616 (awalker@ucdavis.edu)

Pierce’s disease (PD) is caused by the xylem-limited bacteria Xylella fastidiosa (Xf), and is a chronic problem for viticulture in the southern United States and Mexico. PD causes an economic loss of more than $100 million every year just in California. The PD Resistance Grapevine Breeding Program discovered PdR1, a single dominant locus found in a resistant accession from Monterrey, Mexico. The PdR1 locus has been introgressed successfully into different Vitis vinifera varieties while maintaining strong resistance to common wild types of X. fastidiosa. A mutated strain of Xf Temecula 1 was recently developed in Dr. Abhaya Dandekar’s lab to study its secreted virulence factors. This hypervirulent strain (prtA-) exhibits reduced cell length and hypermobility in grapevines, leading to early onset of PD symptoms. However, it is currently unknown how grapevines with the PdR1 locus will respond to this strain. In this work, we investigate the effects of the prtA- strain in highly resistant accessions carrying the PdR1 locus. We are phenotyping at three different time points using the cane maturation index (CMI) and leaf scorch-leaf loss (LS-LL) index. We are also quantifying bacterial titers using ELISA and quantitative-PCR from cane tissue. These results will provide insight into the mechanism of action of PdR1 and its ability to defend against the Xf prtA- strain.

We gratefully acknowledge research funding from the CDFA Pierce’s Disease Board.

Funding Support: CDFA PD/GWSS Board