Identification of QTLS for sunburn resilience in grapevine berries

Abstract

Context and purpose of the study – Grape sunburn is an abiotic stress response triggered by high temperatures. In European cool-climate wine-growing regions, heat stress events are intensifying in their frequency, due to climate change. This stresses grape berries, causing browning and shriveling and results in yield losses and diminished wine quality. Traditional management practices, such as defoliation in the cluster zone to reduce fungal pressure, may exacerbate this issue. Developing climate-adapted cultivars with resilience to sunburn could address these trade-offs for the vineyard management. Some fungus-resistant varieties (PIWIs), like Calardis Blanc, were recently identified to shown notable sunburn resilience. Establishment of vineyards with such culivars that combine protection against abiotic and biotic stress, can help to secure yield and wine quality for a future-proof sustainable viticulture. This study identifies two significant QTLs associated with sunburn damage based on field trials to gain knowledge for genetic factors and highlights the potential and challenges of breeding sunburn-resistant grape plants through marker-assisted selection (MAS).

Material and methods – For this study, a biparental F1 mapping population of Calardis Musqué x Villard Blanc (CMxVB), comprised of 150 genotypes, was investigated at the JKI Geilweilerhof in Siebeldingen, Germany. New SSR markers were developed for the genomic regions associated with loci on chromosomes 10 and 11 and incorporated into an existing genetic map. Sunburn assessments were performed from 2019 to 2023, with damage evaluated each year based on the OIV descriptor 404 for “thermal stress”, whenever symptoms became evident.

Results – Composite interval mapping (CIM) using the revised genetic map and five years of phenotypic field data on sunburn damage identified two significant QTLs. One was located on the lower arm of chromosome 11, with LODmax values reaching 16.3 and one on chromosome 10, with a LODmax value of 10.29. The highest sunburn resilience in berries was linked to the additive effects of an optimal allelic combination at both loci. The results show the high genetic influence while the ripening stage during the heat event revealed to be of minor importance. The QTL regions were further analyzed for annotated and expressed genes in developing grape berries, providing insights into potential mechanisms underlying sunburn resilience.