Evaluating Rootstock Performance: Efficiency and Stability Insights from a 16-Year Moscato bianco Study

Grapevine rootstocks play an essential role in shaping the performance and sustainability of viticulture by influencing key traits such as disease resistance, vine vigor, yield, and fruit quality attributes, including sugar content and organic acid composition (Chen et al. 2024). As a result, selecting an appropriate rootstock has become a cornerstone of modern viticultural practices. Rootstocks affect grapevine physiology by modulating nutrient uptake, water-use efficiency, and photosynthetic performance, all of which contribute to enhancements in scion vigor and yield. For instance, improvements in nitrogen uptake capacity (Keller et al. 2001a, 2001b, Cochetel et al. 2017), water-use efficiency (Pou et al. 2022, Bernardo et al. 2025), and photosynthetic capacity (Soar et al. 2006) have been associated with rootstock selection, demonstrating their influence on grapevine performance. A growing body of research has evaluated the effect of rootstock on scion vigor, yield, and fruit quality traits (Walker et al. 2007, Kviklys et al. 2012, Kodur et al. 2013, Tecchio et al. 2022). However, the interaction between rootstock and scion often exhibits phenotypic variability such as higher yield accompanied by reduced sugar content, which complicates generalized evaluations of rootstock performance. In response to this challenge, efforts have been made to more systematically quantify rootstock contributions; for example, an index based on nitrogen uptake capacity has been proposed (Kulmann et al. 2020). While such indices provide a valuable starting point, they focus on isolated performance traits, emphasizing the need for more comprehensive frameworks that capture the multifactorial nature of rootstock performance. Environmental factors, including annual climatic variability and scion genotype, further compound the complexity of evaluating rootstock efficacy. It has been demonstrated that environmental conditions can exert effects on vine vigor, yield, and fruit quality that are 1.9 to 6.3 times greater than the influence of rootstock (Migicovsky et al. 2021), highlighting the critical importance of conducting long-term studies to ensure reliable and transferable insights. This variability underscores the necessity of adopting performance indices that can integrate multiyear data and account for environmental heterogeneity. To address these gaps, this study introduces two novel indices, the Rootstock Efficiency Index (REI) and the Rootstock Stabil-ity Index (RSI), designed to provide a holistic and accessible approach to evaluating grapevine rootstock performance. These indices synthesize data on scion vigor, yield, and fruit quality, offering a comprehensive yet practical means to assess rootstock performance under diverse environmental conditions. To validate their applicability, this study used a 16-yr data set collected in the Piedmont region of Italy, focusing on Muscat & agrave; petits grains blancs, a commercially significant scion variety that was grafted onto 10 rootstocks. As the trial was conducted in Italy, where the variety is locally known as Moscato bianco, this designation is used hereafter for consistency. Moscato bianco is used widely in sparkling wine production and is valued for its naturally high acidity and low pH, qualities that contribute to freshness in sparkling wines (Kerslake et al. 2014). Measured traits included yield components, pruning weight, vine balance (yield-to-pruning weight ratio), fruit quality metrics, and disease incidence, thereby capturing a wide array of factors that influence vine performance.By leveraging this long-term data set, the proposed indices can bridge the gap between trait-specific assessments and comprehensive performance evaluations. This approach not only provides a robust framework for rootstock selection, it also facilitates development of rootstocks tailored to meet the challenges of climate variability and evolving viticultural demands.