Location: Crops Pathology and Genetics Research
2013 Annual Report
There are 4 main trunk diseases of grape: Eutypa dieback, Esca, Phomopsis dieback, and Botryosphaeria dieback. Collectively, these diseases are the main driver of vineyard decline in California. Every vineyard is or will be affected by trunk diseases. They kill spurs and other sections of the permanent woody structure of the vine from which fruiting shoots originate. Yield losses accumulate over time, thereby reducing the productive life of a vineyard. Our lab is focused on developing early detection tools for trunk diseases, so growers can quickly identify infected vines in the field. Our first greenhouse experiment defined the early stage of infection by Neofusicoccum parvum, the causal agent of Botryosphaeria dieback. The spatial and temporal distributions in the grapevine stem of fungal structures and xylem occlusions (tyloses, gels) give us insight into the stages of infection. At the inoculation site, the pathogen primarily colonized xylem cells (fibers, vessels, rays) and, to a lesser extent, phloem, periderm, and pith. Xylem occlusions were at their highest concentrations where fungal colonization is greatest, at the inoculation site. Full tyloses were at their peak at the inoculation site until 1 month post-inoculation (MPI). At 1.5 MPI, recovery of the pathogen was possible at 2 cm above and below the inoculation site, albeit from only 17% of plants. At 2 MPI, the pathogen spread to 67% of plants at 2 cm below the inoculation site. This movement of the pathogen beyond the inoculation site coincided with increasing levels of vessels with full gels and full tyloses at 2 cm below the inoculation site. Therefore, we define the early stage of infection as the point before the pathogen begins to spread beyond the inoculation site, i.e., before 2 MPI, but also when the plant anatomical response to infection is apparent. Ongoing analyses of differential gene expression in the leaves will hopefully reveal grape expression patterns that are unique to 0.5 and 1 MPI, which is before the pathogen begins to spread. These complimentary approaches of RNAseq, in addition to high-resolution computed tomography (HRCT) of the stems are meant to give us a more comprehensive understanding of the host response than we might find if we only examined the microscopic changes in the stem.