Location: Crops Pathology and Genetics ResearchTitle: Drought exacerbates Botryosphaeria Dieback symptoms in grapevines and confounds host-based molecular markers of infection by Neofusicoccum parvum
|Galarneau, Erin - UNIVERSITY OF CALIFORNIA|
|Lawrence, Daniel - UNIVERSITY OF CALIFORNIA|
|Travadon, Renaud - UNIVERSITY OF CALIFORNIA|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2019
Publication Date: 7/19/2019
Citation: Galarneau, E.R., Lawrence, D.P., Travadon, R., Baumgartner, K. 2019. Drought exacerbates Botryosphaeria Dieback symptoms in grapevines and confounds host-based molecular markers of infection by Neofusicoccum parvum. Plant Disease. 103(7):1738-1745. https://doi.org/10.1094/PDIS-09-18-1549-RE.
Interpretive Summary: Grapevine trunk diseases impact the vine’s ability to transport water and soil-derived nutrients from the roots up to the shoots. We might expect, therefore, that drought would make trunk diseases worse because both affect water relations. We tested a molecular technique to identify the causal pathogen of grapevine trunk disease Botryosphaeria dieback, Neofusicoccum parvum, on vines that were also or only under drought stress. In this way, we could test the specificity of the technique to the pathogen alone. Because this technique targets plant genes during infection, the influence of the pathogen, drought, and their interaction is important. Woody stems of potted ‘Cabernet-Sauvignon’ were inoculated after wounding (IW), with non-inoculated wounded (NIW) and non-inoculated non-wounded (NINW) plants as controls. At 2 weeks post-inoculation (WPI), half of the plants were severely stressed (SS), based on weekly leaf water potentials, receiving 30% water volume of the well-watered (WW) plants. A significant interactive effect of inoculation and water treatments revealed larger lesions among IW-SS plants, but not among other treatments. Expression levels of a set of reported genes were analyzed from leaf samples by qPCR at 2 WPI (before drought stress), and at 8 and 12 WPI (6 and 10 weeks post-stress, respectively) to determine the effectiveness of these host-based molecular markers of infection. Before drought was imposed, no markers were differentially expressed among treatments. One marker showed consistent overexpression at 8 WPI in only IW plants, regardless of water treatment, suggesting specificity to N. parvum infection. By 12 WPI, seven markers showed higher expression in SS plants regardless of inoculation treatment. These results highlight the difficulty to develop disease-diagnostic tools for grapevines in the field, where deficit irrigation is a common part of the growing season and is sometimes imposed to enhance wine quality.
Technical Abstract: Neofusicoccum parvum, causal fungus of the grapevine trunk disease Botryosphaeria dieback, attacks the wood of Vitis vinifera. Because lesions are internal, using putative host-based markers of infection from leaves for diagnosis is a nondestructive option. However, their specificity under drought stress is unknown. Potted ‘Cabernet-Sauvignon’ were inoculated with N. parvum in the greenhouse after wounding (IW), and with wounded and nonwounded noninoculated controls. At 2 weeks postinoculation (WPI), half of the plants were severely stressed (SS), receiving 30% water volume of the well-watered (WW) plants. Larger lesions at 12WPI among IW-SS plants, compared with all other treatments, revealed an interactive effect of inoculation and drought on lesion length. Expression of eight putative marker genes was analyzed in leaves by qPCR at the onset of drought stress, and at 8 and 12 WPI. One marker showed consistent over-expression at 8WPI in IWplants, regardless of water treatment, suggesting specificity to infection. By 12 WPI, higher expression of seven genes in all SS plants (across inoculation treatments) revealed specificity to drought. Cross-reactivity of markers to drought, therefore, limits their utility for disease diagnosis in the field, where drought induced by climate and deficit irrigation is common.