The host guides morphogenesis and stomatal targeting in the grapevine pathogen Plasmopara viticola

Abstract

The oomycete grape downy mildew (Plasmopara viticola Berk. & Curt. Ex de Bary) is a serious pathogen of grapevine and spreads by extremely efficient cycles of asexual propagation. The high efficiency must involve efficient sensing of the host. We therefore analyzed the time course and morphology of the early development of this pathogen in a host system, by infection of leaf discs of grapevine (Vitis vinifera L. cv. Müller-Thurgau), and in a host-free system. Host factors were demonstrated to influence pathogen development in the following ways: (i) the release of zoospores from mature sporangia was accelerated, (ii) the morphogenesis of the germ tube was coordinated, and (iii) the zoospores were targeted to the stomata by factors that depended on stomata closure. The findings show that the early development of P. viticola is regulated, specifically and coordinately, by factors originating from the host plant.

An Extended Leaf Disc Test for Virulence Assessment in Plasmopara Viticola and Detection of Downy Mildew Resistance in Vitis

“…The fact that sporulation was found in some of the leaf discs suggests that there might not be a strong physiological defense in this genotype, and that its resistance is mainly due to this mechanical protection. This contradicts previous reports [40] where the formation of long surface mycelia is described. We never observed long external mycelia, but rather a very low number of encysted spores with normal germ tubes entering into the stomata and forming normal hyphae with haustoria.…”

“…Microscopy showed similar results to those reported in the literature, where shortly after penetration into the substomatal cavity, resistant hosts were able to inhibit the pathogen development [24,26,40]. The response of A. japonica to the infection was similar to that reported on M. rotundifolia [24].…”

“…Although numerous studies [12,24,34,40,41] have been conducted on the interaction between P. viticola and Vitis species and cultivars in the last years, still many questions remain unanswered. Which factors are able to hinder the hyphal growth on the resistant species?…”

Evaluation of resistance to downy mildew in grapevine genetic resources

“…Many studies on the resistance against downy mildew were performed under laboratory conditions using the method of inoculation on leaf discs (Stein et al, 1985;Staudt and Kassemeyer, 1995), leaves (Kiefer et al, 2002), and/or whole plants (Rumbolz et al, 2002).…”

The Compatible Interaction in Downy Mildew Infections

“…With downy mildews, however, such chemical or physical topography factors have yet to be determined (Kiefer et al, 2002). Evidence for host influence on germination of conidia is provided by data showing differential germination rates of Peronospora hyoscyami on different Nicotiana species, which might be explained by availablility of cations (Johnson, 1988).…”