Salinity and calcium effects on emergence, growth and mineral composition of seedlings of eight citrus rootstocks

Salt tolerance of several citrus rootstocks during emergence and the early seedling stage of development was studied under greenhouse conditions. Salinity delayed and depressed seedling emergence, reduced shoot and root biomasses, and altered the mineral concentration of young citrus seedlings, although the magnitude of these changes differed between rootstocks. The addition of 50 mol m'3 NaCl to a nutrient solution delayed seedling emergence by three to five days with the exception of Troyer citrange (TC). Final emergence was reduced by less than 30% in Carrizo citrange (CC), TC, and Swingle cit- rumelo (SC), and by more than 65% in Ridge pineapple (RP), Cleopatra mandarin (CM), and rough lemon (RL). In the 50 mol m~3 NaCl treatment, shoot and root biomass were reduced by over 50%. Even in the no-salt control treatment, emergence of the first seedling and time to 50% emergence varied between rootstocks. Troyer citrange seedlings emerged fastest beginning ten days after sowing. Carrizo citrange and SC emerged on day 16 followed by sour orange (SO) and Volkamer Lemon (VL) at day 20. RP, CM, and RL were the slowest to emerge. The addition of NaCl increased Na, Cl, N, P, and K but reduced Ca and Mg in the shoots of most rootstocks. The addition of 5 mol m~3 CaS04 to the saline solution enhanced the emergence of the first seedling in CC, CM, and RL, improved final emergence in SO, SC, RP, CM, and RL, and improved seedling growth of SC and RL. No uniform trend was found between salt tolerance during emergence and that during seedling growth. Salt tolerance at emergence might not be a useful indicator for the rapid screening of citrus cultivars.