Long-term drought adaptation of unirrigated grapevines (Vitis vinifera L.)

Abstract

Resilience to drought stress is an important crop selection and breeding target particularly under an environment of increasing freshwater scarcities resulting from higher evapotranspiration rates and reduced precipitation. Identifying new genetic material and clones with superior drought tolerance would increase available genetic resources and germplasm for both grapevine breeders and propagators, providing genetic material that has greater water use efficiency thereby reducing reliance on supplemental irrigation. Towards this goal, we explored the long-term drought adaptation of field-grown, unirrigated (or dry-grown) and own-rooted grapevines of pre-clonal origin from shallow (SR) and deep (DR) soils representing low and high soil water availability, respectively, in a South Australian vineyard. Despite lower soil moisture available to SR vines, both deep and shallow-rooted vines had similar vine water status, based on measurements of midday stem water potential ({Psi }_{s}), and leaf net photosynthesis (An). Due to the lower stomatal conductance (gs), SR had higher intrinsic water use efficiency (WUEi) than DR, however the carbon isotope ratio ({delta }^{13}C) of the fruit at harvest was similar between the two groups. Our observations suggest a degree of drought adaptation in the SR vines resulting from multi-decadal cyclical droughts. Overall, we demonstrate that pre-clonal Cabernet Sauvignon grapevines dry-grown in shallow soils have an enhanced resilience to drought compared to dry-grown vines in deep soils. This study has implications for selection of crop genetic material in a changing climate.