Intra-varietal difference in Plasmopara viticola susceptibility under field conditions

Abstract

Intra-varietal diversity has been widely studied to improve the adaptability of Vitis vinifera cultivars to climate change, which is altering cultivation conditions, agricultural practices and suitable growing areas. Downy mildew (Plasmopara viticola), one of the most damaging diseases in vineyards, is increasing in regions traditionally considered dry due to shifts in rainfall patterns that concentrate precipitation during periods of high susceptibility. While varietal susceptibility has been studied in depth, clonal susceptibility remains largely unexplored. The objective of this work was to assess intra-varietal differences in the susceptibility to Plasmopara viticola in four grape varieties. In order to achieve this objective, a field study was conducted in 2025, a year marked by climatic conditions highly favourable to the development of downy mildew and associated with severe yield losses across the DOCa Rioja.

A total of 33 Tempranillo, 15 Graciano, 24 Viura and 28 Garnacha Blanca clones were evaluated in an experimental vineyard. Disease incidence was assessed as the percentage of affected bunches. Results showed the highest downy mildew incidence in Tempranillo and the lowest incidence in Garnacha Blanca. Furthermore, significant intra-varietal variability was observed. The incidence of the disease exhibited significant variation among the different grape varieties, with a range of 61% in Tempranillo, 41% in Graciano, 50% in Viura, and 36% in Garnacha Blanca. For instance, the clone most susceptible to this disease was identified as VN11 (cv. Tempranillo), while the less susceptible was the clone 942 (cv. Graciano).

These findings indicate clear differential clonal susceptibility and support the development of further investigations aimed at identifying clones with lower susceptibility to this disease within the framework of clonal selection programs.

Acknowledgements

This work is part of the research project PID2022-138638OB-I00 funded by MICIU/AEI/10.13039/501100011033. This work was co-supported by the European Regional Development Fund (ERDF), granted to the Autonomous Community of La Rioja within the ERDF Operational Program 2021–2027 (project number: 03-25).