Impact of phenolic compounds on progression of Xylella fastidiosa infections in susceptible and PdR1-locus containing resistant grapevines

Characterization of data observing Meloidogyne incognita, Neofusicoccum parvum, and Xylella fastidiosa infection effects on development of grapevine phenolic compound levels and resistance to subsequent Neofusicoccum parvum infections

Grapevines encounter many different pathogens throughout their lifespans, including the bacterial pathogen Xylella fastidiosa, which causes Pierce's disease that results in vascular occlusion and eventual plant host death, the fungal pathogen Neofusicoccum parvum, which causes stem cankers that kill individual vines and reduce fruit yields, and the root knot nematode Meloidogyne incognita, which destroys root tissues that impacts host vigour. To date, little research has been conducted to examine how one infection could impact subsequent infections by the same or different pathogens despite this is important to ensure healthy vineyards. Therefore, grapevines initially infected with either X. fastidiosa, N. parvum, or M. incognita were subsequently infected with N. parvum eight weeks later to observe developing lesion lengths, which were assessed to determine grapevine resistance to infections. Collected data shows that when prior infections were present, the N. parvum lesions lengths were smaller. This suggests grapevines had induced resistance to combat infections. Further, defence-associated phenolics were measured by high-performance liquid chromatography to determine roles in observed resistance to the secondary N. parvum infections. Data shows that of the different phenolics examined, only stilbenoids were different due to infections, with lowered levels observed in plants that were infected compared with non-infected controls. These data provide insight into how infections by different pathogens could impact grapevine host resistance to new, subsequent pathogen infections.

Pre-inoculation water deficit effects on grapevine physiology, Xylella fastidiosa titers, and Pierce's disease progression

Drought and Pierce's disease are common throughout many grapevine-growing regions such as Mexico and the United States. Yet, how ongoing water deficits affect infections of Xylella fastidiosa, the causal agent of Pierce's disease, is poorly understood. Symptoms were observed to be significantly more severe in water-stressed plants one month after X. fastidiosa inoculation, and, in one experiment, titers were significantly lower in water-stressed than well-watered grapevines. Host chemistry examinations revealed overall amino acid and phenolic levels did not statistically differ due to water deficits, but sugar levels were significantly greater in water stressed than well-watered plants. Results highlight the need to especially manage Pierce's disease spread in grapevines experiencing drought.

Mixed infections of fungal trunk pathogens and induced systemic phenolic compound production in grapevines

As grapevines mature in California vineyards they accumulate chronic wood infections by the Ascomycete fungi that cause trunk diseases, including Botryosphaeria dieback (caused by Diplodia seriata and Neofusicoccum parvum) and Esca (caused by Phaeomoniella chlamydospora). It is thought that such mixed infections become localized to separate internal lesions/cankers of the permanent, woody structure of an individual vine, but nonetheless the fungi all colonize the same vascular system. In response to infection by one pathogen, the host may initiate systemic biochemical changes, which in turn may affect the extent of subsequent infections by other pathogens. To test this hypothesis, we measured changes in phenolic compounds in the wood and lesion lengths of the pathogens, during sequential co-inoculations with different or identical pair-wise sequences of infection by D. seriata, N. parvum, or P. chlamydospora. Prior fungal infections only affected the development of subsequent D. seriata infections. Effects of fungal infections on phenolic compounds were variable, yet initial infection by D. seriata was associated with significantly higher concentrations of most phenolic compounds distally, compared to all other initial inoculation treatments. It was hypothesized that pre-existing phenolic levels can slow initial lesion development of fungal trunk pathogens, especially for D. seriata, but over time the pathogens appeared to overcome or neutralize phenolic compounds and grow unimpeded. These results demonstrate that effects of one fungal trunk pathogen infection is generally unable to distally affect another long-term, albeit shifts in host phenolics and other plant defenses do occur.