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Jude W. Grosser*, J.L. Chandler, and R.M. Goodrich

Sweet orange (Citrus sinensis L. Osbeck) is the most horticulturally important and widely grown Citrus species in Florida and worldwide, and `Valencia' is the most important cultivar for processing. Frozen concentrate orange juice has been the primary product of the Florida and Brazilian industries, but recently there has been a strong shift to not from concentrate (NFC) product in Florida. The higher quality NFC has a greater consumer appeal, and brings a higher market price. The development of higher quality oranges with expanded maturity dates will facilitate this change and should increase the competitive ability of the Florida industry. No true sweet orange cultivars have been developed by conventional breeding due to biological impediments, and alternative methods to obtain genetic variation are being investigated, including studies of somaclonal variation. We have produced nearly 1000 somaclones of `Valencia' sweet orange using organogenesis, somatic embryogenesis, and protoplasts. Following several years of fruit evaluation, early and late maturing high quality somaclones have been identified based on juice analytical data (brix, acid, ratio, juice percentage, juice color, and lbs. solids). These clones have also performed exceptionally in taste panel evaluations comparing them with the traditional mid- and late-season cultivars. Second generation trees of the most promising clones have been propagated for further evaluation, and superior processing clones will be released to the Florida industry in the near future. An overview of this program including pilot plant juice quality data and taste panel results will be presented.

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J.W. Grosser, J. Jiang, E.S. Louzada, J.L. Chandler, and F.G. Gmitter Jr.

Production of tetraploid somatic hybrids that combine complementary diploid rootstock germplasm via protoplast fusion has become a practical strategy for citrus rootstock improvement, with the overall objective of packaging necessary disease and pest resistance into horticulturally desirable, widely adapted rootstocks. Citrus somatic hybridization techniques have been advanced to the point where numerous somatic hybrid rootstocks can now be produced and propagated for evaluation on a timely basis. Herein we report the production of 11 new somatic hybrid rootstock candidates from 12 different parents, including Milam lemon hybrid (Citrus jambhiri Lush.), Cleopatra mandarin (C. reticulata Blanco), sour orange (C. aurantium L.), `Succari' sweet orange [C. sinensis (L.) Osbeck], `Redblush' grapefruit (C. paradisi Macf.), `Nova' tangelo [C. reticulata × (C. paradisi × C. reticulata)], `Kinkoji' (C. obovoidea Hort. Ex Takahashi), Swingle citrumelo [C. paradisi × Poncirus trifoliata (L.) Raf.], Carrizo citrange (C. sinensis × P. trifoliata), rough lemon 8166 (C. jambhiri), and Palestine sweet lime (C. limettoides Tan.). All hybrids were confirmed by cytological and VNTR-PCR analyses, and have been propagated, budded with a commercial scion, and field-planted for performance evaluation.

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Milton D. Taylor, Sarah A. White, Stewart L. Chandler, Stephen J. Klaine, and Ted Whitwell

Substantial quantities of water and nutrients are required for the production of high value nursery and greenhouse crops. As water quality criteria are strengthened locally and nationally, horticultural enterprises will have to meet stricter limits on nutrients in discharge water. This study examined the efficacy of an established vegetated surface-flow constructed wetland to mediate nitrogen (N) and phosphorus (P) in runoff water from a commercial nursery over a period of 38 months. Maximum oxidized nitrogen [nitrate-N (NO3-N) + nitrite-N (NO2-N)] inputs occurred during the spring fertilization period of March through May (11.1 to 29.9 mg·L–1 N) and minimum inputs occurred during winter plant dormancy between December and February (2.8 to 5.2 mg·L–1 N). Nitrogen remediation efficiency averaged 94.7% for March through November sampling dates but declined to a mean of 70.7% between December and February when mean wetland water temperature dropped below 15 °C. Orthophosphate phosphorus (PO4-P) concentrations in nursery runoff showed no dramatic changes over months, seasons, or years. Mean wetland influent orthophosphate concentration ranged from 0.7 to 2.2 mg·L–1 PO4-P with an overall mean of 1.41 mg·L–1 PO4-P for all months sampled. Mean discharge orthophosphate concentration ranged from 0.5 to 2.1 mg·L–1 PO4-P with a mean of 1.45 mg·L–1 PO4-P. Phosphorus remediation efficiency varied widely and there was no correlation with water temperature. This 9.31-acre surface-flow constructed wetland was highly efficient at removing N from nursery runoff from a 120-acre catchment (large container production area), although it failed to consistently lower orthophosphate levels in runoff. This type of constructed wetland is suitable for removing oxidized N forms from nursery runoff and, depending on size, is capable of handling the large volumes of runoff generated by medium to large nursery and greenhouse operations.

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Jude W. Grosser, Frederick G. Gmitter Jr., Franca Sesto, Xiu Xin Deng, and J.L. Chandler

Protoplasm culture following polyethylene glycol (PEG) -induced fusion resulted in the regeneration of somatic hybrid plants from the following six parental combinations: Citrus sinermis (L.) Osbeck cv. Hamlin + Severinia buxifolia (Poir.) Tenore (Chinese box-orange); C. reticulate Blanco cv. Cleopatra + Poncirus trifoliata (L.) Raf. cv. Flying Dragon; C. reticulate cv. Cleopatra + Swingle citrumelo (C. paradisi Macf. × P. trifoliata); C. sinensis cv. Hamlin + C. jambhiri cv. Rough lemon; C. sinensis cv. Valencia + C. jambhiri cv. Rough lemon; and C. paradisi cv. Thompson + `Murcott' tangor (purported hybrid of C. reticulate × C. sinensis). Diploid plants were regenerated from nonfused embryogenic culture-derived protoplasts of `Cleopatra' mandarin and `Hamlin' and `Valencia' sweet orange, and from nonfused leaf-derived protoplasts of Rough lemon and `Mnrcott'. Regenerated plants were classified according to leaf morphology, chromosome number, and isozyme analyses. All of the somatic hybrids reported herein are tetraploid (2n = 4x = 36), with the exception of the `Hamlin' + S. buxifolia hybrid, which was unexpectedly found to have a chromosome number of 2n = 27. These six new somatic hybrids have potential in citrus scion and rootstock improvement for commercial use.

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Jude W. Grosser, Frederick G. Gmitter Jr., J.L. Chandler, and Eliezer S. Louzada

Protoplasm culture following polyethylene glycol-induced fusion resulted in the regeneration of tetraploid somatic hybrid plants from the following attempted parental combinations: Cleopatra mandarin (Citrus reticulata Blanco) + Argentine trifoliate orange [Poncirus trifoliata (L.) Raf.]; `Succari' sweet orange [C. sinensis (L.) Osb.] + Argentine trifoliate orange; sour orange (C. aurantium L.) + Flying Dragon trifoliate orange (P. trifolita); sour orange + Rangpur (C. limonia Osb.); and Milam lemon (purported sexual hybrid of C. jambhiri Lush × C. sinensis) + Sun Chu Sha mandarin (C. reticulate Blanco). Protoplasm isolation, fusion, and culture were conducted according to previously published methods. Regenerated plants were classified according to leaf morphology, chromosome number, and peroxidase, phosphoglucomutase, and phosphoglucose isomerase leaf isozyme profiles. All of the somatic hybrid plants were tetraploid, as expected (2n = 4x = 36), and all five selections have been propagated and entered into commercial citrus rootstock trials.

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Brent L. Black, Harry J. Swartz, Gerald F. Deitzer, Bryan Butler, and Craig K. Chandler

The effect of altered red/far-red light environment on subsequent field performance of strawberry plug plants was tested. Two wavelength-selective plastic films were compared to neutral shade and full-sun control for conditioning `Chandler' strawberry plug plants before transplanting to a winter production system. The following year, plug plants of `Chandler', `Sweet Charlie', and `Allstar' were conditioned under the same treatments, with the addition of a continuous incandescent light and a short-day photoperiod, and plant performance was followed in the winter production system in Florida, a cold-climate annual hill system in Maryland, and in a low-input greenhouse production system. During the first year, the red light-filtering film slightly advanced fruiting in Florida. However, during the second year, the effect of the red light-filtering film was not significant, and a short-day treatment resulted in a greater reduction in runnering and increased early crown and flower development. For June-bearing strawberry plants maintained above 20 °C, altering the red/far-red environment did not consistently advance flowering.

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Jude W. Grosser, Frederick G. Gmitter Jr., E.S. Louzada, and J.L. Chandler

Allotetraploid somatic hybrid plants of `Nova' tangelo [a sexual hybrid of `Clementine mandarin (C. reticulata Blanco) × `Orlando' tangelo (C. reticulata × C. paradisi Macf.)] + `Succari' sweet orange (C. sinensis L. Osbeck), and `Hamlin' sweet orange (C. sinensis L. Osbeck) + `Dancy' tangerine (C. reticulata) were regenerated following protoplast fusion. `Nova' and `Hamlin' protoplasts were isolated from ovule-derived embryogenic callus and suspension cultures, respectively, and fused using a polyethylene glycol method with seedling leaf-derived protoplasts of `Succari' and `Dancy', respectively. Plants were regenerated via somatic embryogenesis, and somatic hybrids were identified on the basis of leaf morphology, root-tip cell chromosome number, and electrophoretic analysis of peroxidase and phosphoglucose mutase isozyme banding patterns. Diploid plants were regenerated from unfused protoplasts of `Hamlin', `Nova', and `Succari'. Tetraploid plants of `Hamlin' and `Succari' were also recovered, apparently resulting from homokaryotic fusions. No `Dancy' plants were recovered. The somatic hybrid and autotetraploid plants can be used for interploid hybridization with selected monoembryonic scions to generate improved seedless triploid tangor/tangelo cultivars. The lack of suitable tetraploid breeding parents has previously inhibited the development of quality seedless cultivars by this method.

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Jude Grosser, Milicia Calovic, Patricia Serrano, Fred Gmitter Jr., and J. L. Chandler

The international fresh citrus market now demands high-quality, seedless fruit that must also be easy to peel for consumer convenience, especially when considering new mandarin varieties. High quality varieties that historically perform well in Florida are generally seedy. Florida is therefore losing market-share to `Clementine' and other seedless varieties produced in Mediterranean climates, including Spain, Morocco, and California. In our ongoing program, somatic hybridization and cybridization via protoplast fusion are now playing a key role in strategies to develop competitive seedless mandarin hybrids adapted to Florida. Somatic hybridization is being used to combine elite diploid parents to produce high quality allotetraploid breeding parents that can be used in interploid crosses to generate seedless triploids. Several thousand triploid mandarin hybrids have been produced under the direction of F.G. Gmitter, Jr. Some of our allotetraploid somatic hybrids are producing fruit with direct cultivar potential, i.e., 'Valencia' sweet orange + `Murcott' tangor. New somatic hybrids produced in our program will be discussed, including `Page' tangor + `Dancy' mandarin, `Page' tangor + `Kinnow' mandarin, and `Hamlin' sweet orange + LB8-9 tangelo. Somatic cybridization is being used to transfer CMS (cytoplasmic male sterility) from the seedless `Satsuma' mandarin to other seedy varieties via mtDNA transfer, in efforts to make them seedless. New somatic cybrids produced in our program that contain the `Satsuma' CMS include `Murcott' tangor and `Kinnow' mandarin. Details of these results and other progress will be discussed.

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Richard L. Bell, T. van der Zwet, C.K. Chandler, and J.C. Scheerens

`Potomac' has been released as a new pear cultivar which combines a high level of resistance to fire blight with excellent fruit quality. Selected from a cross of `Moonglow' × `Beurre d'Anjou', it was tested under the seedling number, US 62537-048. Fruit are ovate-pyriform in shape, and average 73mm in diameter. Skin color is light green and the finish is glossy at harvest maturity, which occurs about 2 weeks after `Bartlett'. Flesh texture is moderately fine, buttery, and juicy; grit cells are small and limited to a thin layer under the skin. Flavor is subacid, with mild aroma, and similar in character to `Beurre d'Anjou'. Fruit may be ripened after harvest without cold storage, but `Potomac' is more susceptible to superficial scald than Beurre d'Anjou if stored for more than eight weeks. The tree is moderately vigorous. Yield and precocity are moderate. Fire blight resistance is greater than that of `Seckel', with a high degree of resistance in both shoots and blossoms. The cultivar is recommended for home orchards and limited commercial trial.

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D. Kirschbaum, D.J. Cantliffe, C.K. Chandler, and R.L. Darnell

The present research was undertaken to examine carbohydrate composition and distribution patterns and induction of flowering and runner formation in attached and detached strawberry plants grown under varying temperature conditions. There was an interaction between attached mother and daughter plants. Daughter plants affected flowering in mother plants, and mother plants influenced vegetative growth in daughter plants. Attachment and high temperature decreased root soluble carbohydrate concentration and promoted runner formation in both mother and daughter attached plants, suggesting that changes in carbohydrate concentration in the roots may be correlated with changes in vegetative growth. According to the results of this research, high temperatures are likely to enhance vegetative growth, whereas lower temperatures are likely to enhance the floral response. Differential temperature regimes applied to the mother/daughter plant experimental system could be an alternative to photoperiod treatments as a tool to study the correlation between environmental conditions and changes in vegetative and reproductive growth in strawberry.