How long is long enough? Robust ranking of commercial grapevine rootstocks and insights for pre-commercial selections from multi-year data

Abstract

In viticulture, the evaluation of scion varieties and rootstocks relies on multi-site field trials that must be maintained and monitored for several years once the vineyards become productive. Such trials are costly and resource-demanding, so it would be valuable to know how long they need to be maintained to provide meaningful results. However, we have little evidence of how long a trial must last to reach robust and reliable conclusions. To shed light on this question, in this work we analysed yield data from a 10-year Tempranillo trial that included both commercial and newly developed rootstocks to quantify how the number of evaluated years affects the robustness of rootstock performance rankings.

The dataset was analysed using several complementary approaches. For each possible trial duration from two to ten years, all combinations of years were treated as partial series and their rankings compared with that obtained from the complete 10-year dataset. Rank-based statistics, including Kendall’s τ and pairwise inversion rate were used to quantify stability. To assess the robustness of conclusions across different trial durations, we also applied leave-one-year-out and leave-k-years-out simulations. The analyses of commercial rootstocks performance revealed a rapid increase in stability with the number of evaluated years, followed by a plateau beyond a certain duration. In contrast, newly developed selections displayed slower convergence and lower stability at comparable trial lengths, suggesting that longer evaluations are needed to reach equivalent reliability.

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Acknowledgments

This long-term evaluation was made possible thanks to the concurrent support of several funding sources, including the Government of Navarra’s programmes Vit-Foot, Vit-Feet and Best-Feet; the CIEN-CDTI initiative LowpHwine, and the cross-border cooperation projects EFA 324/19 – VITES QUALITAS and EFA 033/01 – VITRES (both co-financed at 65 % by the European Regional Development Fund through the Interreg V-A Spain–France–Andorra programme). We are also deeply grateful to all the technical and field staff at Vitis Navarra for their dedication and support in maintaining the trial over the full evaluation period.