Photosynthetic Cost Associated With Induced Defense to Plasmopara viticola in Grapevine

Abstract

Downy mildew caused by Plasmopara viticola is one of the most destructive diseases of Vitis vinifera worldwide. Grapevine breeding programs have introgressed P. viticolaresistant traits into cultivated V. vinifera genotypes and launched interspecific hybrids with resistance against downy mildew. In general, pathogen infection affects primary metabolism, reduces plant growth and development and modifies the secondary metabolism toward defense responses, which are costly in terms of carbon production and utilization. The objective of this work was to evaluate the photosynthesis impairment by inducible defenses at the leaf level in V. vinifera cultivars resistant to P. viticola. Photosynthetic limitations imposed by P. viticola in susceptible and resistant grapevine cultivars were evaluated. Histochemical localization of hydrogen peroxide and superoxide and the activity of ascorbate peroxidase were assessed. Measurements of leaf gas exchange, chlorophyll fluorescence and the response of leaf CO 2 assimilation to increasing air CO 2 concentrations were taken, and photosynthetic limitations determined in cultivars Solaris (resistant) and Riesling (susceptible). The net photosynthetic rates were reduced (−25%) in inoculated Solaris plants even before the appearance of cell death-like hypersensitive reactions ("HR"). One day after "HR" visualization, the net photosynthetic rate of Solaris was reduced by 57% compared with healthy plants. A similar pattern was noticed in resistant Cabernet Blanc and Phoenix plants. While the susceptible cultivars did not show any variation in leaf gas exchange before the appearance of visual symptoms, drastic reductions in net photosynthetic rate and stomatal conductance were found in diseased plants 12 days after inoculation. Decreases in the maximum Rubisco carboxylation rate and photochemical impairment were noticed in Riesling after inoculation with P. viticola, which were not found in Solaris. Damage to the photochemical reactions of photosynthesis was likely associated with the oxidative burst found in resistant cultivars within the first 24 h after inoculation. Both chlorophyll degradation and stomatal closure were also noticed in the incompatible interaction. Taken together, our data clearly revealed that the defense response against P. viticola causes a photosynthetic cost to grapevines, which is not reversible even 12 days after the pathogen infection.

Screening of Croatian Native Grapevine Varieties for Susceptibility to Plasmopara viticola Using Leaf Disc Bioassay, Chlorophyll Fluorescence, and Multispectral Imaging

“…Despite these circumstances, only 24 h after inoculation did this parameter clearly distinguish infected from non-infected leaf discs ( Figure 1 a), which is much earlier than the previous finding where the earliest change of F v /F m pattern on Chardonnay leaves appeared four days upon inoculation [ 38 ]. Here, necrotic areas were observed four days after inoculation in cultivar Solaris, which is in accordance with previous research [ 39 ], in which low F v /F m value was found five days after inoculation due to the development of necrotic spots.…”

“…Novel phenotyping methods which include chlorophyll fluorescence and multispectral imaging were previously used for quantification of different plant diseases such as Blumeria graminis in barley [ 35 ], Cercospora beticola in sugar beet [ 36 ], and Puccinia triticina in wheat [ 37 ]. Screening for susceptibility to P. viticola among V. vinifera varieties was also performed by these methods [ 38 , 39 ]. Recently, alterations of primary metabolism induced by pathogenesis have been the focus of studies.…”

The Molecular Priming of Defense Responses is Differently Regulated in Grapevine Genotypes Following Elicitor Application against Powdery Mildew

“…It is known that metabolic responses to Erysiphe necator can vary greatly among Vitis species [9], but information on intraspecies variability-mediated phenomena involved in the regulation of either susceptibility or resistance to this pathogen is still limited. Conversely, this subject was widely explored in relation to grape downy mildew [58,59].…”

Mono-Locus and Pyramided Resistant Grapevine Cultivars Reveal Early Putative Biomarkers Upon Artificial Inoculation With Plasmopara viticola

“…DM affects the members of the family Vitaceae and in particular the cultivated species Vitis vinifera and it can attack all green parts of the vine (leaves, fruits, and shoots in particular) (Buonassisi et al, 2018;Vezzulli et al, 2018). DM infection leads to significant crop losses due to defoliation and to the production of lowquality, deformed or entirely damaged grapes (Yildirim et al, 2019;Nogueira Júnior et al, 2020). The most distinctive signs of infection are the sporangia formation apparent as whitish spots, commonly found on the abaxial surface of the first-formed leaves, which are accompanied by chlorotic spots (known also as oil spots) on the adaxial surface.…”