Evaluation of 21 new disease-resistant winegrape varieties (PIWI) for viticultural suitability in north-eastern Italy

Abstract

The cultivation of disease-resistant winegrape varieties (PIWI) is gaining interest worldwide, particularly in viticultural areas where the use of fungicide is limited. Most breeding programs have focused primarily on resistance to pathogens, while yield performance and fruit composition across different environments, especially under global warming conditions, have received much less attention. This study evaluated yield components and fruit composition of 21 disease-resistant grapevine varieties grown under three training systems over ten consecutive vintages (2015–2025) in an experimental vineyard in Castelfranco Veneto, north-eastern Italy. The 11 white varieties included Aromera, Bronner, Fleurtai, Johanniter, Muscaris, Sauvignon Kretos, Sauvignon Nepis, Sauvignon Rytos, Solaris, Soreli and Souvignier gris. The 10 red varieties were Monarch, Cabernet Carbon, Cabernet Volos, Cabernet Eidos, Julius, Merlot Kantus, Merlot Korus, Prior, UD 31-103 and Vinera. Mean yield was similar between white and red varieties, averaging 2.65 kg per vine. Among white varieties, the lowest yields were recorded for Sauvignon Nepis and Aromera (1.72 and 1.81 kg per vine, respectively), while among red varieties the lowest values were observed for Cabernet Carbon, Merlot Korus and Merlot Kanthus (1.93, 2.19 and 2.14 kg per vine, respectively). These varieties were characterized by smaller clusters and lower cluster numbers, which accounted for their reduced yield. At harvest, average total soluble solids were 20.5 °Brix in white varieties and 20.1 °Brix in red varieties, while titratable acidity averaged 7.1 g L⁻¹ and 7.6 g L⁻¹, respectively. The lowest acidity levels were found in Soreli and Fleurtai (5.8 and 6.2 g L⁻¹). Overall, all resistant varieties reached technological maturity with adequate sugar levels while maintaining acceptable acidity. The resistant varieties proved well suited to the local environment, characterized by high annual rainfall (> 1000 mm) and warm growing conditions (~1900 °C growing degree days). Bronner and Sauvignon Rytos (white), as well as Cabernet Carbon and UD 31-103 (red), showed high phenotypic stability across all the productive traits evaluated, as indicated by regression coefficients close to or below 1. In contrast, Sauvignon Rytos (white) and Merlot Kanthus (red) exhibited low phenotypic stability, displaying a strong response to vintage conditions and high inter-annual variability. However, in particularly hot vintages, such as 2016, white varieties showed rapid sugar accumulation accompanied by a marked decline in acidity (2.6 g L⁻¹ in Fleurtai), raising concerns about their future suitability under projected climate warming.