YOUNG APPLE TREES RESPONSE TO WATER STRESS - EARLY RESULTS

The fruit production zone in the south of Uruguay presents very limited water resources so that growers must develop strategies to maximize the return of applied water. In the winter of 2006, an experiment with apple trees (Malus x domestica ‘Royal Gala’) grafted on M9 was installed in a frame of 4×1.25 m. From 2007/2008 season, four irrigation treatments were applied, consisting of increasing levels of stress, covering the 100, 66, and 33% of the ETc and without irrigation, only rain fed. By mid-December, the stem water potential already presented significant differences (p=0.05) between the non-irrigated and the irrigated treatments, but with no differences amongst the irrigated treatments. A month later, differences between all the treatments were shown. The vegetative growth, both the length of the shoots and the trunk section still did not present differences between the treatments by the end of the summer of 2009. Nevertheless, the weekly increase of the fruits size showed significant differences between treatments, being smaller in the non-irrigated trees in all the dates. The first harvest, obtained in 2009, showed significant differences in the yield between the two more irrigated treatments and the non-irrigated one. The treatment irrigated to 33% of the ETc had an intermediate production. The yield differences were due not only to a greater fruit number per tree but also, mainly, to a larger size of the fruits. Indeed, the three irrigated treatments had significantly bigger fruits compared to the non- irrigated, but without differences amongst them. These early results suggest that, faced with water shortage, irrigation deficit could be handled covering only 66% of the ETc affecting neither the production nor the structure of the trees.