Drought stress phenotyping for rootstock breeding: a case study in Vitis berlandieri

The development of lime-tolerant, phylloxera- and drought-resistant rootstocks is the major goal of present breeding programmes. One approach to phenotype the response to drought stress during hot and dry summers is the analysis of the ratio of ¹³C and ¹²C isotopes in the juice sugar of the grapevine. This low effort approach is a simple and robust indicator for the behaviour of the stomatal apparatus, thus a proxy for the drought stress response of the grapevine during berry maturation. However, unlike cultivated grapevines, hermaphroditism is not the norm in wild Vitis species. To analyse the grapevine performance under drought conditions for those that do not bear fruit, i.e., accessions displaying male flowers, the analysis of carbon isotopes in the annual pruning wood may be a suitable alternative. Therefore, carbon isotope discrimination (δ¹³C) was conducted on the juice of 90, single-harvested, fruit bearing V. berlandieri accessions of the Geisenheim University wild Vitis collection. Additionally, one-year-old pruning wood was sampled from the same individual grapevines during winter and also analysed for the ¹³C:¹²C ratio of the woody shoot tissue. Regression analysis was conducted to describe the relationship between the parameters measured. The phenotyping approach of the analysis of annual pruning wood mass δ¹³C appears to be a promising proxy for an easy to conduct, cost-efficient and seasonal independent, thus versatile applicable method that further provides useful information on the drought stress response of non-fruit bearing grapevines. The method is interesting for the pre-selection of breeding partners aspired for rootstock breeding programmes. Additional data shall be collected to increase the validity of the approach tested.