|Detecting the grapevine wood-canker pathogen Neofusicoccum parvum (Botryosphaeria dieback) based on host markers of infection|
E. R. GALARNEAU (1), S. Czemmel (2), R. Travadon (3), G. Cramer (2), A. J. McElrone (1), K. Baumgartner (1). (1) USDA-ARS CPGRU Davis, Davis, CA, U.S.A.; (2) University of Nevada-Reno, Reno, NV, U.S.A.; (3) University of California-Davis, Davis, CA, U.S.A.
Botryosphaeria dieback (causal fungus <i>Neofusicoccum parvum</i>) is a wood-canker disease that limits vineyard productivity. Early detection is hampered by the internal nature of the canker and absence of leaf symptoms. A detection tool for the early stage of infection, and from leaves instead of wood, would inform control practices. We defined the early stage of infection of inoculated vs. non-inoculated (both wounded and non-wounded) plants, based on light microscopic investigation of: 1) fungal colonization at and beyond the inoculation site, and 2) plant anatomical responses to wood colonization. Then we identified differentially-expressed genes from newly-expanding leaves that were specific to the early stage of infection, based on RNA-seq. Fungal colonization occurred in the xylem, mostly the fibers, and was restricted to the inoculation site until 2 months post-inoculation (MPI). Also at 2 MPI, a significantly higher percentage of xylem vessels fully-occluded by gels and xylem tissue with lower starch content were quantified in inoculated plants, but not in wounded or non-wounded plants. RNA-seq analysis of leaves identified 2,340 differentially-expressed candidate genes. qPCR analysis showed genes that were significantly induced and maintained at high levels in the early stages of infection were associated with plant defense responses, such as: 1) altered gene regulation, 2) cell wall modification, and 3) adaptation of amino acid biosynthesis.