Salinity and Supplemental Calcium Influence Growth of Rabbiteye and Southern Highbush Blueberry

`Tifblue' and `Brightwell' rabbiteye blueberries (Vaccinium ashei Reade.) were subjected to 0, 25, or 100 mM Na + , as Na 2 SO 4 or NaCl, and 0, 1, 3, or 10 mM supplemental Ca 2+ , primarily as CaSO 4 , in an irrigated sand culture in the greenhouse. Additionally, the effect of NaCl on `Sharpblue' southern highbush blueberry (primarily V. corymbosum L.) was examined. For unsalinized plants, fastest growth occurred in plants not receiving supplemental Ca 2+ . Root and shoot growth were depressed as salinity increased in plants lacking additional Ca 2+ . With 100 mM Na + as Na 2 SO 4 . `Tifblue' root and shoot dry weight increases were only 37% and 25%, respectively, of the increase of unsalinized controls, while with 100 mM Na + as NaCl, the corresponding shoot and root dry weight increases were only 38% and 43%, respectively. `Brightwell' plants reacted similarly to `Tifblue' in salinity treatments with Na 2 SO 4 and NaCl, but `Sharpblue' plants were more severely affected by 100 mM NaCl than were the rabbiteye cultivars. In no case did addition of Ca 2+ have any ameliorative effect on either the dry weight of roots of plants exposed to 25 or 100 mM NaCl or on the shoot growth of plants exposed to NaCl. The inability of Ca 2+ to counter Cl- entry or toxicity may account for the lack of amelioration. In contrast, additional Ca 2+ did improve shoot growth of plants exposed to Na 2 SO 4 . For `Tifblue' plants supplied with 25 mM Na + as Na 2 SO 4 , growth increased by almost 25% in the presence of 10 mM Ca 2+ , while for `Tifblue' plants treated with 100 mM Na + as Na 2 SO 4 , growth was more than three times greater in plants supplied with 1 mM Ca than in those not given any Ca 2+ . Growth increase was primarily due to increased leaf area and number. Low (1 mM) concentrations of Ca 2+ were more effective in ameliorating the effects of 100 mM Na + as Na 2 SO 4 than were 3- and 10-mM Ca 2+ supplements, possibly because higher Ca 2+ additions lead to metabolic damage in these calcifuge Vaccinium species.