Relaunch of the PIWI grapevine breeding program at Geisenheim University

Abstract

The development of disease-resistant grapevine cultivars (PIWI) has become a key strategy to reduce fungicide inputs, increase climateresilience, and meet regulatory and societal demands for sustainable viticulture. While substantial progress has been achieved in recent decades, further genetic gain and accelerated breeding cycles are required to ensure practical implementation and market acceptance.

In 2023, the grapevine breeding program at Hochschule Geisenheim University (HGU) was relaunched, continuing a long-standing tradition that began in the 1960s and was interrupted between 2000 and 2023. The renewed program builds on valuable legacy breedingmaterial with strong resistance backgrounds and favorable viticultural traits, complemented by the integration of modern PIWI parentsto broaden genetic diversity and performance.

The main breeding objectives are stable resistance to downy mildew (Plasmopara viticola), powdery mildew (Erysiphe necator), and black rot (Guignardia bidwellii), combined with high wine quality and agronomic suitability, including yield stability, growth habit, and favorable phenological traits. Amulti-stage breeding funnel is implemented, combining targeted parental selection, classical cross-breeding, and large seedling populations with successive phenotypic and genotypic selection steps. Early selection is based onartificial inoculation and natural infection, supported by established resistance markers (Rpv, Ren, Rgb). To accelerate genetic gain, innovative approaches such as early parental recycling and location-based grafting are applied to shorten generation intervals.

In parallel, the program is developing a structured reference population that will serve as the basis for future data-driven breeding. Systematic multi-site phenotyping and standardized trait recording are being established to capture genetic variation for disease resistance, agronomic performance and quality traits under diverse environmental conditions. These data will gradually be complemented by high-throughput genotyping and digital phenotyping approaches implemented at HGU. The long-term goal is to enable the use of predictive breeding approaches to support parental selection and early-stage seedling evaluation, particularly for complex traits that are costly or time-consuming to measure directly.

Since its restart, the program has expanded from a single cross in 2023 to 35 successful crosses in 2025, with initial resistance screeningsalready identifying highly resistant seedlings. Although advanced field trials are still under establishment, the program provides a foundation for a modern, predictive breeding strategy contributing to long-term sustainable viticulture and regional breeding capacity.