Melogoldʼ Pummelo X Grapefruit Hybrids on Nine Rootstocks on A
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CROP PRODUCTION HORTSCIENCE 39(1):28–32. 2004. (Cleo, C. reticulata Blanco) x trifoliate orange (Poncirus trifoliata L.) hybrid originating in South Africa (Castle et al., 1993b) were ob- Performance of ‘Oroblancoʼ and tained from the FDACS Division of Plant In- dustry. Seedlings of Carrizo citrange (Carrizo, ‘Melogoldʼ Pummelo x Grapefruit C. sinensis Osbeck x P. trifoliata); Cleo; Goutou (an unidentifi ed Citrus hybrid); rough lemon Hybrids on Nine Rootstocks on a 8166 (RL-8166, C. limon L.); Smooth Flat Se- ville (SFS, an unidentifi ed Citrus hybrid); Sun Chu Sha mandarin (SCS, C. reticulata Blanco), Calcareous, Poorly Drained Soil Swingle citrumelo (Swingle, C. paradisi x P. Ed Stover1, Robert Pelosi, Michael Burton, Scott Ciliento, and trifoliata); and Volkamer lemon (Volk, C. limon L.) were produced by collecting seed Mark Ritenour from source trees and sowing them in soilless University of Florida, IFAS, Indian River Research and Education Center, mix in Feb. 1992. Rootstock seedlings were Fort Pierce, FL 34945 grown in the greenhouse using frequent irriga- tion and fertilization, with pest control provided Additional index words. citrandarin, citrange, citrumelo, Citrus grandis, Citrus paradisi, as needed. In Nov. 1992, when seedlings were Citrus reticulata, Florida, fruit quality, grapefruit, Indian River, parthenocarpy, perched 7–10 mm in diameter, they were T-budded at water table, pummelo, triploid, x639 15 cm above the soil line. Young trees were Abstract. Adjacent but separate trials of ʼOroblancoʼ and ‘Melogoldʼ, both triploid pum- maintained in the greenhouse and were fi eld melo [Citrus grandis (L.) Osbeck] x grapefruit (Citrus paradisi Macf.) hybrids, were es- planted in July 1993. tablished on nine rootstocks in the Indian River citrus region of Florida in 1993. The trees Field site and cultural practices. Plant- on the citrandarin rootstock x639 [Cleopatra mandarin (C. reticulata Blanco) x trifoliate ings were made at the Indian River Research orange (Poncirus trifoliata L.)] were signifi cantly more productive than trees on any other and Education Center in Ft. Pierce, Fla. The rootstock tested for ‘Oroblancoʼ and all rootstocks except Swingle citrumelo (C. paradisi orchards were established as separate but x P. trifoliata) and Cleopatra mandarin for ‘Melogoldʼ. Cumulative production of ‘Oro- contiguous rootstock trials for ‘Oroblancoʼ blancoʼ on x639, through year 9, was 50% higher than for Swingle or Volkamer lemon and ‘Melogoldʼ using a randomized com- [C. limon (L.)], which were the next highest in yield. ‘Melogoldʼ displayed extremely low plete-block design, with six blocks in each yield, with 45% of trees producing fewer than 50 fruit total in the 9 years of this study. trial and two-tree plots of each rootstock. Carrizo citrange (C. sinensis Osbeck x P. trifoliata) produced the smallest trees with both Blocks were established so that drainage was scion varieties, refl ecting poor adaptation of this rootstock to the calcareous soil at the as similar as possible within each block. Typical trial site. As expected, acidity of ‘Oroblancoʼ and ‘Melogoldʼ was much lower than would of older Indian River region citrus orchards, be observed for grapefruit when fall harvested, with similar total soluble solids (TSS), the planting site had been formed into single- and much higher TSS : titratable acidity ratio. Some rootstock effects on internal quality row beds to improve drainage, and had been were observed. planted to citrus since 1934. Spacing was 9.2 m between rows and 5.4 m within rows. The siteʼs soil was mapped as primarily Winder The Indian River region of Florida is noted been evaluated in California and elicited con- sand depressional (fine-loamy, siliceous, for its production of high quality fresh market siderable grower and market interest. hyperthermic, typic glossaqualfs) with some grapefruit (Citrus paradisi Macf.), which has The loss of sour orange as a standard inclusions of Wabasso sand (sandy, siliceous, been largely produced on sour orange (Citrus rootstock for the Indian River area, because hyperthermic, alfi c haploquads). Microsprin- aurantium L.) rootstock. Minimum standards of its susceptibility to decline strains of citrus kler irrigation was used. Fertilization and pest of sugar content and sugar : acid ratio must be tristeza virus, remains the greatest horticul- control were typical of grapefruit grown for met before grapefruit can be legally marketed tural problem for this regionʼs citrus industry, processing in the Indian River area. (Citrus Administrative Committee, 2003b). and no ideal replacement for sour orange has Data collection. From 1998 through 2002, While a few orchards may meet these stan- been identifi ed (Stover and Castle, 2002). the total number and weight of fruit were re- dards as early as September in some years, Rootstocks that are industry standards in other corded for each tree when harvested in October the availability of salable grapefruit is usually areas of Florida are either poorly adapted to through December of each year. Beginning in substantially less than the potential market until the calcareous, poorly drained soils common September, ‘Oroblancoʼ fruit were sampled on late October (e.g., Citrus Administrative Com- in the Indian River region or do not confer 3–4 dates each year to test internal fruit qual- mittee, 2003a) in most years. Many grapefruit premium internal fruit quality. ity characteristics, with number and weight of producers think that an earlier ripening grape- The purpose of the trials described in this fruit and source tree recorded for inclusion in fruit or grapefruit-like hybrid may provide a paper was twofold: fi rst, to assess yield and overall yield data. Cropping was so poor on substantial benefi t by providing an expanded fruit quality of ‘Oroblancoʼ and ‘Melogoldʼ ‘Melogoldʼ that sampling for fruit quality was market season. in Florida, and second, to compare their restricted to a single date each year. Internal Plant breeders in California released two performance on both standard rootstocks and quality tests on each date were conducted using pummelo [Citrus grandis (L.) Osbeck] x grape- potentially superior rootstocks being consid- 10 fruit from each of three trees of each sampled fruit hybrids in the 1980s (Soost and Cameron, ered for wider planting. rootstock. These fruit quality samples were 1980, 1985), which are similar in fl avor and compared to fruit samples from nearby plant- appearance to grapefruit, but are earlier ripen- Materials and Methods ings of standard grapefruit varieties. Quality ing and are seedless triploids. These hybrids, variables collected at each sampling included known as ‘Oroblancoʼ and ‘Melogoldʼ, had Tree preparation. Budwood of ‘Oroblancoʼ percent juice following hand squeezing, total and ‘Melogoldʼ was obtained from the Cali- soluble solids (TSS; measured using a bench- fornia Citrus Clonal Protection Program and top, temperature-compensated refractometer; Received for publication 8 July 2003. Accepted placed in the Florida Dept. of Agriculture and Spectronic Instruments, Rochester, N.Y.), for publication 2 Sept. 2003. This research was supported by the Florida Agricultural Experiment Consumer Services (FDACS) Citrus Germ- percent titratable acidity (TA; measured using Station, and approved for publication as Journal plasm Introduction Program for pathogen in- a Mettler titrator, model DL12, Hightstown, Series No.R-09551. dexing. It was approved for release in Florida N.J.), and ratio of TSS : TA. On 7 Dec. 2001, 1To whom reprint requests should be addressed. E- in Nov. 1992. 10 fruit at fi nal harvest were randomly selected mail address: [email protected]fl .edu Seedlings of x639, a Cleopatra mandarin from each ‘Oroblancoʼ tree and were assessed 28 HORTSCIENCE, VOL. 39(1), FEBRUARY 2004 6-00042, p28-32 28 2/17/04, 10:11:05 AM for presence of vesicle drying. In Jan. 2003, soils have a hardpan at <60 cm, which results in For ‘Melogoldʼ, trees on Volk, x639, RL-8166, following harvest in the ninth year of these a perched water table that is sometimes within and Cleo were in the largest category for both plantings, data were collected on tree height, 25 cm of the soil surface even on bedded groves height and canopy volume (Table 2). width (east–west and north–south), trunk cross- and is likely to infl uence tree growth (Boman, Yield and fruit size of ‘Oroblancoʼ. Com- sectional area (TCSA) above the bud union, 1987). Between 1993 and 2002, tree loss was mercially signifi cant croploads were borne on and tree mortality. No data were collected on not signifi cantly different between rootstocks ‘Oroblancoʼ trees beginning in 1998, 5 years cause of tree mortality. in this experiment, with no more than two of 12 after planting (Fig. 1). Average yield across Statistical analysis. Yield data are presented trees lost for any rootstock/scion combination all rootstocks reached 98 kg per tree in 2001 as production per tree for the surviving trees. (data not shown). By Fall 2002, ‘Oroblancoʼ (Fig. 1), which was substantially less than the Data comparing effect of rootstock on cumula- trees were similar in height on all rootstocks 210 kg per tree considered a standard yield tive production of >50 fruit on ‘Melogoldʼ were except Carrizo, which produced smaller trees for 5- to 15-year-old grapefruit in the Indian analyzed using chi-square analysis. All other with a mean height of 3 m vs. heights of River area (Muraro et al., 2002). Only the trees data were analyzed by analysis of variance 3.4–3.8 m among the other rootstocks (Table on x639 produced yields approaching 200 kg (ANOVA) using ProcGLM (SAS Institute, 1). Canopy volume of ‘Oroblancoʼ trees on per tree, and only in 2001 (Fig.1). Trees on Cary, N.C.). Where the treatments were found x639 was the greatest among the rootstocks x639 produced signifi cantly higher cumulative signifi cantly different at P ≤ 0.05, means were tested, but only trees on Carrizo and RL-8166 numbers of fruit and yield than any of the other separated using DMRT.