Water content is often not a good parameter for tree quality

In an EU-financed project the effects of desiccation and moisture re-absorption on regrowth were assessed and the reliability of some parameters for assessing regrowth potential of desiccated woody plants was checked. For predicting regrowth and thus measuring tree quality vitality as well as dormancy are important aspects. Therefore in two of the three described experiments dormancy was completely released before desiccation treatments (0-30%) of the apple rootstocks (Malus 'M9' (T337) and Malus 'Mh111') started. After dehydration stocks were either or not rehydrated during different periods in a water-saturated root-dip. Water content was monitored and in one experiment regrowth potential was measured by assessing the root electrolyte leakage (REL) and the water potential (WP). After planting days to flushing and survival at the end of the first season were recorded. It is shown that in terms of fresh weight re-wetting can largely overcome desiccation while regrowth potential remains poor. It was concluded that a limited period of re-wetting can improve regrowth after moderate drought stress but that nevertheless moisture content is not a good parameter for regrowth potential of Malus-rootstocks. Only when plants are not re-wetted moisture content may be an indicator for regrowth potential. For measuring regrowth potential it is important to know what is the definition of regrowth, earliness of shooting or total survival after one or more growing seasons.