Abstract
'Hamlin' sweet orange [Citrus sinensis (L.) Osb.] field trials were established at the north (Tavares) or south (Lake Placid) ends of the central Ridge region, and two 'Valencia' trials were established in flatwoods sites near St. Cloud or Immokalee between 1987 and 1991 at conventional tree spacings in soils typical for each region. Trees on 17 to 31 rootstocks, including several commercial rootstocks, were planted at each location in formal replicated experiments or in informal non-replicated arrangements. The rootstocks were mostly citranges [Citrus sinensis × Poncirus trifoliate (L.) Raf.], citrumelos (Citrus paradise Macf. × Poncirus trifoliate), mandarins (Citrus reticulata Blanco), other sexual hybrids and somatic hybrids. Tree survival among the four field studies was generally above 70% but was less than 50% for some rootstocks because of freeze damage in one Central Ridge study and other unknown causes at one flatwoods study. Trees on sour orange and Bittersweet sour orange rootstocks at all locations eventually succumbed to citrus tristeza virus. Tree heights ranged from about 8 to 15 feet, but the relationships were similar among tree heights in those rootstocks that were common to two or more studies. Among the formal replicated experiments, yield was either measured or estimated annually for about 5 years, and 4 years of juice quality data were collected at the Immokalee site. Yield was generally related directly to tree height. 'Hamlin' and 'Valencia' trees on F80-5 citrumelo, Carrizo, Troyer, and C-32 citranges, ×639 (a Cleopatra mandarin × trifoliate orange hybrid) produced some of the highest cumulative yields and were relatively tall trees. 'Valencia' on 1584 [a trifoliate orange × 'Milam' hybrid (Citrus jambhiri Lush.)] was one of the highest yielding combinations. In the Immokalee field trial, juice quality of fruit from trees on Swingle citrumelo did not differ significantly from the juice quality of fruit from trees on most of the other citrange, citrumelo, and mandarin rootstocks. Based on tree survival, growth, and cumulative yield, promising rootstocks were ×639, 1584, certain numbered citrumelos, and 'Flying Dragon' trifoliate orange when considered as a rootstock for high density plantings. No differences were observed between trees on Carrizo or Troyer citranges, or between Cleopatra or Sun Chu Sha mandarins.
