December 1, 1996
Seed of 17 citrus varieties that have been used commercially or tested as rootstocks were obtained from the Florida Department of Agriculture, Division of Plant Industry, Citrus Budwood Office at Winter Haven. Seeds were germinated on a temperature gradient table in sand media maintained at a temperature gradient from 60 to 100 degrees Fahrenheit (ordm;F). Seed varieties were sour orange, Smooth Flat Seville, Citrus obovoidea, Gou Tou #1, Zhu Luan, Cleopatra mandarin, Sun Chu Sha, X-639, Ridge Pineapple, Carrizo citrange, Benton citrange, C-35 citrange, Swingle citrumelo, F80-18 citrumelo, Rangpur lime × Troyer citrange, rough lemon, and Poncirus trifoliata. Optimum temperatures for germination ranged from 77ordm; for P. trifoliata to 90.5ordm;F for Rangpur × Troyer. The mean of optimum germination temperatures for all varieties was 85.5ordm;F. Mean germination time and percentage seed germinated were recorded and used in the formula to determine optimum temperature for germination.