|SHUGART, HOLLY - Pennsylvania State University|
|GUTIERREZ, JOSE - Fresno State University|
|WALKER, M. ANDREW - University Of California, Davis|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2021
Publication Date: 9/8/2021
Citation: Backus, E.A., Shugart, H.J., Gutierrez, J., Walker, M. 2021. Field-collected glassy-winged sharpshooters perform more Xylella fastidiosa-inoculating behaviors on susceptible Vitis vinifera cv. ‘Chardonnay’ than on resistant Vitis champinii grapevines. Journal of Economic Entomology. Available: https://doi.org/10.1093/jee/toab141.
Interpretive Summary: Pierce’s disease (PD) is a lethal scorching disease of grapevines caused by the bacterium Xylella fastidiosa (Xf),which threatens the $5 billion per year grape crop in the state of California. Sharpshooter leafhoppers and froghoppers (adult spittlebugs) transmit Xf. The introduction of the glassy-winged sharpshooter (GWSS) in the 1980’s worsened the situation with PD. The state of California has been spending over $100 million per year since the early 2000’s to control PD, chiefly by vector control through quarantines, biological control, and insecticide applications. A major effort between the University of California, Davis and the USDA Agricultural Research Service was initiated in 2001 to develop PD-resistant grapevines through classical breeding. The present research explored the possibility of using electropenetrography (EPG) to refine the characterization of grapevines from the breeding project that are susceptible or resistant to infection with Xf. EPG provides a way to visualize insect feeding through graphs obtained by electronic means. GWSS fed differently on grapevine lines. The infection-resistant grapevine was also resistant to vector feeding behaviors responsible for injecting bacteria into the plant; the infection-susceptible grapevine was susceptible to the same behaviors. Thus, EPG detected a novel type of grapevine resistance to PD related to feeding by GWSS and its ability to inoculate Xf. Future research to develop PD-resistant grapevines could incorporate screening for this novel type of grapevine resistance using EPG.
Technical Abstract: The glassy-winged sharpshooter, Homalodisca vitripennis (Germar) arrived in California in the late 1980’s. By 1997, it had greatly worsened the Pierce’s disease (PD) problem for grape vineyards in the southern part of the state. PD is a lethal scorching disease caused by the xylem-dwelling bacterium Xylella fastidiosa Wells et al.(Xanthomonadales: Xanthomonadaceae); bacteria are transmitted by sharpshooter leafhoppers and adult spittlebugs. Once acquired, X. fastidiosa colonizes the functional foregut of the vector. Bacteria can be inoculated directly into grapevine xylem during the xylem 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 through classical breeding. V. arizonica line b43-17 was found to have strong resistance to X. fastidiosa infection. This line also has V. candicans and V. rupestris in its genetic background. The present study used EPG to compare the stylet probing behaviors between V. champinii, a V. candicans/V. rupestris natural hybrid with dense trichomes, and V. vinifera cv. ‘Chardonnay,’ which lacks trichomes. Results found that sharpshooters performed significantly more X waves/X. fastidiosa inoculation behaviors of overall longer duration on Chardonnay than on V. champinii, and that the latter genotype was highly acceptable when trichomes were removed. 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 process that is the basis for most resistance breeding today. Future research could use EPG to screen grapevines for this novel type of resistance.