Abstract

MYBURGH, P.A.  and  HOWELL, C.L.. Determining a Midday Stem Water Potential Threshold for Irrigation of Table Grapes. S. Afr. J. Enol. Vitic. [online]. 2022, vol.43, n.2, pp.96-102. ISSN 2224-7904.  http://dx.doi.org/10.21548/43-2-4700.

Sustainable table grape production depends on sufficient water supply. Water potential is a useful indicator of water constraints in grapevines. In this regard, midday stem water potential (Ψ₈) is considered to be a better indicator of grapevine water status than leaf water potential (*F_L). The objective of the study was to determine a water potential threshold to set soil water refill lines for table grape irrigation. However, in previous studies carried out locally, only *F_L was measured. The relationship between Ψ₈ and *F_L was determined for ten selected table grape cultivars. Since there were no differences between cultivars, a single equation could be used to convert midday *F_L measured in previous studies with table grapes to Ψ₈. Vegetative growth, berry mass and colour, as well as juice total soluble solids (TSS) data were pooled, and related to midday Ψ₈. This showed that -0.8 MPa seems to be a Ψ₈ threshold for water constraints in the pre-harvest period that will allow sustainable growth and berry size for anisohydric table grape cultivars. The optimum Ψ₈ for berry colour is between -0.8 MPa and -1.0 MPa. Consequently, a midday Ψ₈ threshold of -0.8 MPa can be used to set refill points for irrigation where soil water content is measured on a regular basis in table grape vineyards.

Keywords : Berry mass; colour; grapevine; vegetative growth; water potential.

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