Field-Collected Glassy-Winged Sharpshooters (Hemiptera: Cicadellidae) Perform More Xylella fastidiosa-Inoculating Behaviors on Susceptible Vitis vinifera cv. 'Chardonnay' Than on Resistant Vitis champinii Grapevines.

The glassy-winged sharpshooter, Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae: Cicadellinae), is an introduced vector of the xylem-dwelling bacterium Xylella fastidiosa Wells et al. (Xanthomonadales: Xanthomonadaceae) in California. Once acquired, X. fastidiosa colonizes the functional foregut of the vector. Bacteria can be inoculated directly into grapevine xylem during the xylem cell acceptance process in sharpshooter stylet probing, represented by the X wave using electropenetrography (EPG). Since 2001, an effort has been underway to develop PD-resistant grapevines, Vitis vinifera L., through classical breeding of various species of resistant wild grapevines with more susceptible V. vinifera. The present study used EPG to compare H. vitripennis stylet probing behaviors in a factorial experiment between V. champinii (a V. candicans/V. rupestris natural hybrid with moderate trichomes) and V. vinifera cv. 'Chardonnay' (which lacks trichomes) that had been gently scraped to remove trichomes or was not scraped. Results showed that sharpshooters performed significantly more X waves/X. fastidiosa inoculation behaviors of overall longer duration on Chardonnay than on V. champinii, regardless of shaving or not-shaving to remove trichomes. In addition, trichomes caused more frequent standing/walking/test-probing behaviors on V. champinii, whose xylem was rapidly accepted for sharpshooter ingestion once probing began. Thus, EPG can detect a novel type of grapevine resistance to X. fastidiosa-to the vector's probing process and inoculation of bacteria-in addition to the bacterial infection and symptom development processes that are the basis for most resistance breeding today. Future research could use EPG to screen grapevines for this novel type of resistance.