Abstract
This experiment was carried out to determine optimal culture conditions for the production of cut flowers and tubers of Calla (Zantedeschia 'Black Magic') in highlands. To achieve the research purpose, growth of 'Black Magic' Calla influenced by tuber hardness (3.3 and $6.0kg/cm^2$), $GA_3$ concentration (0, 100 and $200mgL^{-1}$), duration of $GA_3$ treatment (24 hr, 12 hr and 30min before planting) were investigated. When tubers have high hardness, those were not severely injured by soft rot disease regardless of $GA_3$ concentrations and treatment durations. Tubers with low tuber hardness showed more than 90% of soft rot occurrence when treated with $200mgL^{-1}$ $GA_3$ for 24 hrs before planting. However, soft rot did not occur when tubers were treated with $200mgL^{-1}$ $GA_3$ for 12 hrs before planting. In conclusion, $GA_3$ treatment results showed soft rot occurrence statistically significant degree in accordance with the bulbs hardness. In addition, the yield of the cut flowers is the result received the greatest effect in accordance with the bulbs in size and appeared to not be determined in accordance with the $GA_3$ treatment concentration and hardness bulbs. To obtain flowers without soft rot symptom, tubers (as $6.0kg/cm^2$) should be completely dried after $GA_3$ treatment.
