Effect of water stress on the reproductive performance of Shiraz (Vitis vinifera L.) grafted to rootstocks

An experiment was conducted in the Barossa Valley, South Australia, to examine the effect of rootstocks on reproductive performance of Shiraz (Vitis vinifera L.) under water stress. Vines were grown on own roots or grafted to 110R, 1103P, 99R, Ramsey, Schwarzmann, or 140Ru. Vines either were unirrigated or irrigation was applied at 56 to 128 mm/ha across three seasons. Water stress (Psi(pd) < 0.8 MPa) was apparent in the unirrigated vines from veraison onward. The absence of irrigation strongly influenced vine growth and performance. Pruning weight, cane weight, and cane number were all reduced as a consequence of zero irrigation. Yields were reduced in unirrigated treatments due to a reduction in cluster number, cluster weight, and berry weight rather than fruit set or berry number. Unirrigated Ramsey was the only rootstock able to maintain yield comparable with irrigated rootstocks. Unirrigated own roots performed well in the first season but not in the second and third seasons when water stress had a negative effect on yield. Millerandage, coulure, and seedless berry numbers were the main reproductive parameters found to have a negative impact on yield and both own-rooted and grafted vines were as susceptible to these parameters. Season had a greater influence than either rootstock type or irrigation. These findings have significant implications for regions facing future drought and declining water supplies