Water relations and cropping of apple cultivars on a dwarfing rootstock in response to imposed drought

SummaryWater relations of 15 scion cultivars of apple (Malus x domestica Borkh.) were compared when grafted on a very drawfing rootstock (M.27). Three of these were studied in detail. Drought was imposed by using under-tree polythene tents to reduce the amount of water reaching the root zone. Some cultivar differences in tree water relations were observed, e.g. ‘James Grieve’ consistently had the highest leaf conductances and the lowest leaf water potentials. Drought decreased growth much more than it decreased fruit yield. The use of family trees (two scions on one rootstock) for increasing the efficiency of scion comparisons was shown to improve the precision of comparisons. Various methods of estimating the water status of the crop were compared, including direct soil moisture measurement with a neutron probe, measurement of leaf water potential on exposed scion leaves, covered scion leaves or leaves on suckers, and estimates of the root surface water potential.