Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 10/23/2019
Publication Date: 12/14/2019
Citation: Krugner, R., Ledbetter, C.A., Rogers, E.E., Burbank, L.P. 2019. Insights for understanding ‘Nemaguard’ immunity mechanism against Xylella fastidiosa. CDFA Pierce's Disease Control Program Research Symposium. p. 133.
Technical Abstract: ‘Nemaguard’ was selected by the USDA and released in 1959 as a rootstock for almond and stone fruits due to resistance to nematodes and enhanced scion vigor. 'Nemaguard’ happens to be resistant to Xylella fastidiosa, the causal agent of almond leaf scorch disease. Previous research showed that prior to June-budding use of this rootstock prevents infection of almond nursery stock by X. fastidiosa. Further, the rootstock also promotes an apparent complete pathogen elimination and remission of leaf scorching symptoms in infected susceptible scions. However, nothing is known about potential chemical and physical mechanisms of resistance to X. fastidiosa infection. The goals of the current study were to determine 1) whether insect vector feeding periods on ‘Nemaguard’ can reduce bacterial populations in vectors or its transmission efficiency to susceptible plants, and 2) evaluate establishment and movement of X. fastidiosa in ‘Nemaguard’ compared to susceptible plants. After acquiring X. fastidiosa from infected grapevines, vector access periods of up to 14 days on ‘Nemaguard’ did not reduce pathogen population densities in vectors or transmission efficiency of X. fastidiosa to susceptible plants when compared to control. Mechanical inoculation of X. fastidiosa to almond resulted in systemic infection and expression of typical almond leaf scorch symptoms, whereas ongoing analysis of ‘Nemaguard’ samples have shown no survival or establishment of X. fastidiosa at or beyond the point of inoculation. Results showed that ‘Nemaguard’ xylem sap does not reduce X. fastidiosa populations in infected vectors, indicating that natural chemical properties of ‘Nemaguard’ xylem sap are not involved in resistance to X. fastidiosa. Collectively, results suggest that future research should focus on identification of potential physical traits that prevent movement of bacterial cells within the plant.