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`Hamlin' orange (Citrus sinensis L. Osbeck) was grown on 15 rootstocks: four citrumelos [C. paradisi Macf. × Poncirus trifoliata (L.) Raf.], five mandarin × trifoliate orange hybrids (C. reticulata Blanco × P. trifoliata), two pummelo × trifoliate orange hybrids [C. grandis (L.) × P. trifoliata], Vangasay lemon (C. limon Burm. f.), Norton citrange (C. sinensis × P. trifoliata), and two Smooth Flat Seville (C. aurantium L. hybrid?) hybrids. These scion–rootstock combinations were compared to trees on Swingle citrumelo, the most widely used citrus rootstock in Florida. One Smooth Flat Seville hybrid was eliminated early because of poor growth and variability in size, and the Vangasay lemon rootstock was eliminated because of severe freeze damage. At age 5, the trees on Norton citrange developed citrus blight and were eliminated. Remaining in the experiment for 7 years, `Hamlin' trees on six of the 13 rootstocks produced more fruit than trees on Swingle citrumelo. Of these six, HRS 852 (Changsha mandarin × English large-flowered trifoliate orange) was the best overall rootstock, with trees on it producing large quantities of high-quality fruit on medium-sized canopies.

Twenty-one selections consisting of 13 numbered hybrids, one ornamental, and seven named cultivars were tested as rootstocks for `Valencia' orange, Citrus sinensis L. Osbeck. The test included six, four-tree replications in randomized complete blocks on sandy soil typical of the center of the Florida peninsula. Trees propagated on Vangasay lemon, HRS 812 (Sunki × Benecke trifoliate orange), and HRS 942 (Sunki × Flying Dragon trifoliate orange) produced more fruit than trees on the other 18 rootstocks in the test. Trees on 10 rootstocks, including the widely used commercial rootstocks, Swingle citrumelo and Carrizo citrange, were intermediate in cumulative fruit production. Trees on five rootstocks, including Sun Chu Sha, Gou Tou #1, and Tachibana, had low yields and trees on HRS 939 (Flying Dragon trifoliate orange × Nakorn pummelo) and sour orange #2 were extremely dwarfed and were minimally productive because of tristeza virus disease. Fouryear cumulative fruit production ranged from 52 to 317 kg per tree. Fruit from trees on HRS 954 and HRS 952 (Pearl tangelo × Flying Dragon trifoliate orange) had the highest, and fruit from trees on Vangasay and Gou Tou #1 had the lowest total soluble solids concentration.

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To determine the levels of elements not usually included in soil analyses, aqua regia extracts from 10 soils in eight locations throughout the Florida citrus belt were analyzed for 14 rare earth elements (lanthanides), scandium, and yttrium with an IGP spectrophotometer. Leaves, bark, wood, and roots of citrus trees growing at two of the sampling locations, a fertilizer (14% N-l.7% P-11.6% K), and a dolomite sample were also analyzed. Scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), and holmium (Ho) were found in the soil samples in amounts above detection limits varying from 0.002 to 0.017 mg/L. Cerium, La, and Nd were the elements present in the largest amounts. The levels showed no particular regional pattern and a great amount of variability, even between adjacent sites at the same location. A soil with a relatively high organic matter content and cation exchange capacity (CEC) (Hallandale soil at Indiantown in South Florida) had by far the highest rare earth content. Lanthanide levels in the citrus tree tissues correlated with soil content, with the highest levels in the feeder roots (range 4.6 to 585.1

Concentrations of N, P, K, Ca, Mg, Na, Fe, Mn, Zn, Cu, Cl, Mo, and Al varied between blight-affected and healthy trees in one or more of the following ‘Valencia’ orange tree (Citrus sinensis (L.) Osb.) tissues: leaves, twigs, branches, trunks, trunk bark, large roots and feeder roots. Blight had no effect on B concentration; watersoluble phenolics were higher in the trunk wood of blight-affected trees, but not in the wood of branches and roots. Differences in cation exchange capacity, pH and 10 available nutrients in the soil were too small to be significant. The water content of the trunk, branch, and root wood did not vary significantly. The most consistent changes with blight were: higher N levels in the bark and the wood of the trunk; lower K levels in the leaves, coupled with higher K in the wood of the branches and the trunk; higher Na in the leaves and the trunk wood, higher Zn in the leaves and trunk wood; higher Cl concentrations in the leaves and the branch wood together with lower concentrations in the feeder roots.

Yield, fruit quality, growth, and the levels of 12 elements in the leaves of 14-year old nucellar ‘Redblush’ grapefruit on 13 rootstocks showed that trees on Citrumelo C.P.B. 4475, ‘Morton’ citrange, and ‘Bittersweet’ sour orange were the most productive; those on ‘Ponkan’ mandarin, seedlings on their own roots, and sour orange were the least productive3. Two-year means of total soluble solids ranged from 10.3% for fruit from trees on ‘Bittersweet’ sour orange, ‘Carrizo’ citrange, and ‘Ponkan’ mandarin to 11.3% on sour orange. Fruit size was best on ‘Bittersweet’ sour orange and on Citrumelo C.P.B. 4475. Effects of rootstock on the levels of N, K, Mg, Mn, Zn, Na, and Cl and B in the leaves were statistically significant.