Assessment of Resistance Components for Improved Phenotyping of Grapevine Varieties Resistant to Downy Mildew

Abstract

Grapevine varieties showing partial resistance to downy mildew, caused by Plasmopara viticola, are a promising alternative to fungicides for disease control. Resistant varieties are obtained through breeding programs aimed at incorporating Rpv loci controlling the quantitative resistance into genotypes characterized by valuable agronomic and wine quality traits by mean of crossing. Traditional phenotyping methods used in these breeding programs are mostly based on the assessment of the resistance level after artificial inoculation of leaf discs in bioassays, by using the visual score proposed in the 2nd Edition of the International Organization of Vine and Wine (OIV) Descriptor List for Grape Varieties and Vitis species (2009). In this work, the OIV score was compared with an alternative approach, not used for the grapevine-downy mildew pathosystem so far, based on the measurement of components of resistance (RCs); 15 grapevine resistant varieties were used in comparison with the susceptible variety ‘Merlot’. OIV scores were significantly correlated with P. viticola infection frequency (IFR), the latent period for the downy mildew (DM) lesions to appear (LP50), and the number of sporangia produced per lesion (SPOR), so that when the OIV score increased (i.e., the resistance level increases), IFR and SPOR decreased, while LP50 increased. The relationship was linear for LP50, monomolecular for IFR and hyperbolic for SPOR. No significant correlation was found between OIV score and DM lesion size, sporangia produced per unit area of lesion, length of infectious period, and infection efficiency of the sporangia produced on DM lesions. The correlation between OIV score and area under the disease progress curve (AUDPC) calculated by using the RCs and a simulation model was significant and fit an inverse exponential function. Based on the results of this study, the measurement of the RCs to P. viticola in grapevine varieties by means of monocyclic, leaf disc bioassays, as well as their incorporation into a model able to simulate their effect on the polycyclic development of DM epidemics in vineyards, represents an improved method for phenotyping resistance level.

Components of partial resistance to Plasmopara viticola enable complete phenotypic characterization of grapevine varieties

“…Therefore, IFR and SPOR, together, were able to distinguish all the four clusters. In addition, since IFR and SPOR are the major drivers of DM epidemic progress in vineyards 69 , which is caused by the concatenation of infection cycles, the phenotyping of partial resistant varieties by using these two RCs in monocyclic experiments would also account for their effect on epidemic development. This would reduce the workload of phenotyping while still producing correct assessment of resistance.…”

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

“…Since leaves are the pioneers in providing the first visual symptoms of the downy mildew disease, phenotyping methods on leaf discs that are inoculated and maintained in controlled conditions have been widely applied among plant pathologists, breeders, and geneticists who are willing to obtain differences between genotypes regarding their downy mildew susceptibility [ 28 , 29 ]. Leaf disc bioassay is based on the International Organisation of Vine and Wine (OIV) descriptor 452-1 (Leaf: degree of resistance to Plasmopara (leaf disc test)) [ 30 ].…”

Colonization of Aspergillus carbonarius and accumulation of ochratoxin A in Vitis vinifera, Vitis labrusca, and hybrid grapes – research on the most promising alternatives for organic viticulture

“…Vitis labrusca and hybrid grapes are known for their higher resistance to downy mildew (caused by Plasmopara viticola ) than V. vinifera 29 . This disease is an important cause of the reduced yield and quality of the grapes.…”