Resistance profiling of PIWI accessions: insights from Geisenheim university’s breeding program

Abstract

Context and purpose of the study. Fungus-resistant grape varieties (PIWIs) represent a significant advancement toward more environmentally sustainable viticulture. Resistance to the primary pathogens Plasmopara viticola and Erysiphe necator, the causal agents of downy mildew (DM) and powdery mildew (PM) in grapevines, has been a major focus of PIWI breeding for over 150 years. This study examines 17 genotypes, selected for their viticultural characteristics and developed at Hochschule Geisenheim University from the late 1970s to the early 2000s. These breeding strains were phenotyped for their resistance and analyzed for the presence of resistance alleles against PM and DM for the most commonly used quantitative trait loci (QTLs). The aim of this study is to evaluate and compare these genotypes to commercial elite cultivars to assess their potential for future breeding programs.

Material and methods. DNA from all 17 accessions was analyzed for key markers related to resistance to Plasmopara viticola (Rpv) and resistance to Erysiphe necator (Ren) at the following loci: Rpv1, Rpv3.1, Rpv3.2, Rpv3.3, Rpv10, Rpv12, Run1, Ren3, and Ren9. The breeding lines and elite cultivars were phenotyped for their resistance using leaf disc assays (DM), evaluations of resistance in potted plants (PM and DM), and field assessments on leaves and grapes (PM).

Results. All 17 accessions exhibited varying degrees of phenotypic resistance. Significant differences were observed in their resistance behavior toward PM and DM, with some accessions outperforming popular elite cultivars such as Cabernet Cortis and Souvignier Gris. The 17 breeding lines exhibited different combinations of Rpv and Ren resistance alleles, with the most commonly encountered alleles being Rpv3.1, Rpv3.3, Rpv10, Ren3, and Ren9. In contrast, Rpv1, Run1, and Rpv12 resistance alleles were not detected in any of the accessions. Notably, some accessions displayed resistance levels much higher than expected based on the analysis of these common markers, making these accessions interesting for future resistance breeding and genetics research.