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Abstract
Trifoliate orange [Poncirus trifoliata (L.) Raf.] and various other commonly-used rootstocks, submitted to long-day (LD) of 16 hours, (normal day + 4 hr incandescent light break), normal day (ND) of 12 hours ± 1 hr 10 min and short-day (SD) of 8 hour photoperiods fell into 2 groups—those which responded to LD tratment and those which did not. Rootstocks in the first group, Christianson, Beneke, Pomeroy, Rubidoux and Yamaguchi, trifoliate orange cultivars; Carrizo and Savage citranges [P. trifoliata × C. sinensis (L.) Osbeck.]; Sacaton citrumelo [P. trifoliata × C. paradisi Macf.]. Hawaiian sweet orange (C. sinensis) and Milam lemon (C. jambhiri Lush.), responded strongly to LD treatments in shoot growth and stem diameter. Rootstocks less responsive to photoperiod include Cleopatra mandarin (C. reshi Hort. ex Tan.), Estes lemon, (C. jambhiri), Troyer citrange, Swingle citrumelo, C. macrophylla Webster, C. taiwanica Tan. and Shin and C. volkameriana Pasq. This second group was considered better adapted to tropical conditions because they made better growth under SD conditions.