Smooth Flat Seville Research Articles

Karyotype variability of sour orange (Citrus aurantium L.) and the origin of its heteromorphic karyotypes

Sour orange (Citrus aurantium L.) is a very well-known citrus product. As sweet orange [Citrus sinensis (L.) Osbeck], it originated from the crossing between mandarin (Citrus reticulata Blanco) and pummelo [Citrus maxima (Burm.) Merril]. In order to investigate the origin and variability of its karyotype, eight cultivars of C. aurantium and one cultivar of Citrus natsudaidai Hayata, closely related to C. aurantium, were characterized with the fluorochromes CMA (chromomycin A3) and DAPI (4′-6-diamidino-2-phenylindole) and FISH (fluorescent in situ hybridization) with 5S and 35S rDNA, as well as BAC (bacterial artificial chromosomes) probes. The sour orange accessions analyzed presented three distinct karyotype formulae, but six of eight accessions had the formula 1A + 1B + 1C + 8D + 7F. Citrus natsudaidai presented the formula 2A + 1C + 6D + 9F. The accessions ‘Smooth Flat Seville’, ‘Standard’, and ‘Thornless’ presented three sites of 35S rDNA in total, in A or B chromosomes, as well as in one D. The accessions ‘Smooth Flat Seville’ and ‘Thornless’ presented always two sites of 5S rDNA, in one F and one D chromosomes. The presence of chromosome types A/35S and F/5S reinforces C. aurantium as a first-generation hybrid derived from C. maxima, while a D/5S-35S chromosome corroborates C. reticulata as a second parent. However, several chromosome changes occurred after the hybridization event, which can be partly explained by the reduction of heterochromatic blocks and partly by the occurrence of introgressions in some accessions.

Hydrogen Cyanamide on Citrus: Preliminary Data on Phytotoxicity and Influence on Flush in Potted and Field Trees

Bloom in individual citrus (Citrus) trees often continues for more than 1 month in south Florida, with even greater bloom duration within most orchard blocks because of variation in bloom timing between trees. Prolonged bloom contributes to variable fruit maturity as harvest approaches and increases severity of postbloom fruit drop (PFD) disease (caused by Colletotrichum acutatum). Hydrogen cyanamide (cyanamide) has been effective in accelerating bloom in various deciduous fruits, and its potential use in citrus was investigated in this preliminary study. Cyanamide was applied at a range of concentrations, from 0% to 1.0% a.i., to potted trees of six citrus types reflecting fairly broad diversity in commercial citrus that was readily available as seed [alemow (Citrus macrophylla), ‘Duncan’ grapefruit (Citrus paradisi), sour orange (Citrus aurantium), ‘Smooth Flat Seville’ sour orange hybrid (C. aurantium hybrid), ‘Swingle’ citrumelo (C. paradisi × Poncirus trifoliata), and ‘Sun Chu Sha’ mandarin (Citrus reticulata)] in Dec. 1999 while trees were quiescent. Phytotoxicity increased with cyanamide rate, with some damage at 0.125% cyanamide on most tested plants, and large variation among citrus types. All cyanamide rates hastened flushing. Airblast application of cyanamide (0, 0.025%, 0.05%, and 0.10%) was made to mature trees of ‘Valencia’ and ‘Navel’ sweet orange (Citrus sinensis) in Ft. Pierce, FL, on 27 Jan. 2000. On 15 Feb. and 28 Feb. additional trees received cyanamide at 0.05%. There was considerable defoliation, which increased linearly with cyanamide rate. Flushing and flowering were unaffected by cyanamide compared with controls except in February where cyanamide applied at 0.05% increased flowers per tree in ‘Valencia’ sweet orange, and in contrast, 0.1% cyanamide on 27 Jan. reduced ‘Navel’ sweet orange flowering. Cyanamide application to ‘Valencia’ sweet orange on 28 Feb., after initial flowering but 16 days before peak bloom, significantly reduced yield per tree but there were no other effects on cropping. In these trials, cyanamide was not an effective agent for hastening bloom in south Florida citrus with applications late January through February. Further work is needed to determine whether December applications of cyanamide to trees in the field may be more effective in concentrating subsequent flush and bloom.

Desempenho da tangerineira 'Span Americana' em diferentes porta-enxertos

Este trabalho objetivou avaliar o crescimento vegetativo, a produção e a qualidade de frutos da tangerina 'Span Americana' em diferentes porta-enxertos, nas condições edafoclimáticas de Bebedouro-SP. O plantio foi realizado em junho de 2003, em espaçamento de 6,0 m x 3,0 m, sendo utilizada irrigação por gotejamento a partir de 2006. Os porta-enxertos avaliados foram: citranges [Citrus sinensis (L.) Osbeck × Poncirus trifoliata L. Raf] 'Carrizo' e 'Troyer', tetraploides; trifoliatas (P. trifoliata) 'Davis A' e 'Flying Dragon'; limão Volkameriano Catania 2 (C. volkameriana Tenn. et Pasq.), HRS 849 [(C. aurantium L. cv. 'Smooth Flat Seville' x P. trifoliata cv. 'Argentina')], tangelo 'Orlando' (C. reticulata Blanco × C. paradisi Macf.) e limão 'Cravo' (C. limonia Osbeck). Foram avaliadas a produção acumulada, a eficiência produtiva e a precocidade de entrada em produção, no período de 2007 a 2009. Avaliaram-se, também, as dimensões das plantas e a taxa média de crescimento das plantas no período de 2005 a 2008, além da qualidade dos frutos em 2006 e 2007. Em pomares irrigados de tangerineira 'Span Americana', os porta-enxertos trifoliata 'Davis A' e HRS 849 apresentam desempenho horticultural satisfatório. Para plantio em alta densidade, a melhor performance da tangerineira 'Span Americana' é obtida com a utilização dos porta-enxertos trifoliata 'Flying Dragon' e citranges 'Troyer' e 'Carrizo'.

Plant growth, leaf photosynthesis, and nutrient‐use efficiency of citrus rootstocks decrease with phosphite supply

AbstractSome formulations of phosphite (Phi) have been recommended as a source of P nutrition for several crops including citrus even though there are known negative effects of Phi on plant growth. Changes in plant growth and metabolism after Phi application should be reflected in altered nutrient‐use efficiency and leaf photosynthesis. We carried out a greenhouse study using seedlings of two contrasting citrus (Citrus spp.) rootstocks, Carrizo citrange (CC) and Smooth Flat Seville (SFS), growing in either aerated hydroponic culture or sterilized native sandy soil. Plants were subjected to four P treatments: No P (control, P0); 0.5 mM Pi (PO4‐P); 0.25 mM Pi + 0.25 mM Phi (Pi + Phi), or 0.5 mM Phi (Phi). Photosynthetic characteristics, concentrations of total P (Pt) and soluble PO4‐P or PO3‐P in leaves and roots, and plant growth were evaluated after 80–83 d P treatments. Overall, the Pi plants had the highest Pt (total P) and total plant dry weight while the P0 plants had the lowest Pt but highest total root length and root‐to‐shoot ratio. Leaf chlorophyll (SPAD readings) and net assimilation of CO2 (ACO2) of the P0 and Phi plants were similarly lower than those of Pi and Pi + Phi plants. Growth responses of the Pi + Phi treatment were intermediate between the Pi and Phi treatments. Although Phi increased Pt and soluble‐PO4‐P concentration in leaves and roots above the P0 treatment, this did not translate into increased plant growth. In fact, the Phi treatment had some phytotoxic symptoms, impaired P‐ and N‐utilization efficiency for biomass production as well as lower nutrient‐use efficiency in the photosynthetic process. Thus, these two rootstocks could not use Phi as a nutritional source of P.

Rootstocks and the Performance and Economic Returns of ‘Hamlin’ Sweet Orange Trees

‘Hamlin’ is a principal sweet orange grown in Florida for processing. It is productive but produces juice with low soluble solids content and poor color. A long-term trial was conducted in central Florida to determine rootstock effects on yield and juice quality and the effect of economic analysis on the interpretation of the horticultural results. The trees were a commonly used commercial selection of ‘Hamlin’ sweet orange [Citrus sinensis (L.) Osb.] propagated on 19 rootstocks planted in a randomized complete block design of three-tree plots with six replicates in a Spodosol soil at a density of 350 trees/ha. Routine horticultural data were collected from the original trial (H1) for 10 years. Trees on some rootstocks that grew and yielded poorly were removed within a few years and replaced with a second trial (H2) with 13 rootstocks from which data were collected for 5 years. The H1 data were financially analyzed to compare the relative usefulness of horticultural and economic data in interpreting results and making rootstock decisions. In H1 after 10 years, tree height ranged from greater than 5 m [Volkamer lemon (C. volkameriana Ten. & Pasq.)] and Cleopatra mandarin (C. reshni Hort. ex Tan.) to 2.4 m {Flying Dragon trifoliate orange [Poncirus trifoliata (L.) Raf. ]}. In H2, the trees on somatic hybrid rootstocks were ≈2 m tall after 8 years and 4.4 m among those on mandarins and C-32 citrange (C. sinensis × P. trifoliata). Tree losses from citrus blight were generally low except for the trees on Carrizo and Troyer citranges (greater than 50%). Horticulturally, the highest performing trees in H1, measured by cumulative yield and soluble solids production over 10 years, were those on Carrizo, Troyer, and Benton citranges; poor performers were those on Smooth Flat Seville and Kinkoji (putative sour orange hybrids). Fruit yield and soluble solids production were directly related to tree height regardless of the difference among rootstocks in juice quality. The same relationship existed among the trees in H2 in which the best rootstocks were C-32 and Morton citranges. Trees on Swingle citrumelo (C. paradisi Macf. × P. trifoliata) ranked no. 12 of 19 rootstocks and 9 of 13 rootstocks in H1 and H2, respectively. Financial interpretation of the outcomes to include tree replacement resulting from blight losses did not substantially change the horticultural interpretations. Additional financial analyses demonstrated that the performance of trees on rootstocks with relatively low productivity/tree, like those on C-35 citrange and Kinkoji, would equal those on more vigorous rootstocks when tree vigor was properly matched with spacing. Yield determined the economic outcomes and financial analysis aided the interpretation of rootstock horticultural effects but did not greatly alter the relationship among rootstock results. Highly significant correlations between annual and cumulative data indicated that relative rootstock performance among ‘Hamlin’ orange trees in Florida could be reliably determined based on the first 4 cropping years.

Trunk Sprouting and Growth of Citrus as Affected by NAA, Aluminum Foil, and Plastic Trunk Wraps

In spring 1999, a commercial NAA (1-naphthaleneacetic acid) preparation for trunk sprout inhibition was compared with a corrugated plastic trunk wrap, aluminum foil wrap, bimonthly hand removal of sprouts, use of NAA preparation plus bimonthly hand removal when sprouts appeared, and a nontreated control. Three recently planted groves on three different rootstocks [`Midsweet' orange (Citrus sinensis)] on Swingle citrumelo (Citrus paradisi × Poncirus trifoliata), `Valencia' orange on Volkamer lemon (Volk, Citrus limon), and `Minneola' tangelo (Citrus paradisi × C. reticulata) on Smooth Flat Seville (SFS, Citrus hybrid) received each of the treatments in a randomized complete block experimental design with trees blocked by initial height and circumference. Every 2 months, sprouts were counted on each tree and removed from the hand removal treatments. After 1 year, all sprouts were removed and counted and height and circumference of trees was determined. Across all experiments, 82% to 100% of nontreated trees produced trunk sprouts and all sprout control methods significantly reduced sprouts per tree. NAA treatments were never significantly less effective at sprout suppression than the wraps at the P = 0.05 level, although in two experiments, wraps were more effective than NAA at P = 0.10. Time of sprout appearance varied between the three experimental blocks. Plastic and foil trunk wraps enhanced development of trunk circumference compared with nontreated controls in `Midsweet'/Swingle and `Valencia'/Volk. Greater trunk circumference resulted from use of wraps versus NAA in all three experiments, which appeared unrelated to differential sprout suppression. In these experiments, it appears that either wraps enhanced tree development beyond the suppression of sprouts or NAA influence on tree metabolism somewhat reduced trunk growth. The economics of the sprout suppression methods are also discussed.

Controlling factors of environmental flooding, soil pH and Diaprepes abbreviatus (L.) root weevil feeding in citrus: Larval survival and larval growth

The underlying influences of soil flooding, pH level and soil-inhabiting Diaprepes abbreviatus (L.) root weevil larval feeding in citrus were examined in two separate greenhouse studies, rootstock × flooding × Diaprepes-larvae (RFD) and liming × rootstock × flooding × Diaprepes-larvae (LRFD). Our objectives were to determine the combined effects of soil flooding and pH level on survival and growth of Diaprepes root weevil larvae to gain insights of insect-environmental relations for the weevil control. We used a Floridana sandy loam (pH 4.8) from a citrus grove infested by Diaprepes root weevil in center Florida. The RFD experiment consisted of two citrus rootstocks (Swingle and Smooth Flat Seville), three flooding durations (0, 20, and 40 days) and two larval infestation rates (0 and 5 larvae) for 40-day feeding. The LRFD experiment consisted of two citrus rootstocks (Swingle and Carrizo), three pH levels (non-limed control, and target pH 6 and 7), two flooding durations (0 and 40 days), and two larval rates (0 and 5 larvae) for 56-day feeding. Dolomite (54% CaCO 3 and 46% MgCO 3) was used for soil liming in the LRFD. Treatments were arranged with 15 replicates in a completely randomized design. In the RFD, flooded soil pH was 0.3 units higher than non-flooded soil and larval survival was the lowest in the longest flooded treatment ( P < 0.05). In the LRFD, soil pH increased 0.5–0.9 units for the target pH 6, and 0.7–1.1 units for the target pH 7. The effects of rootstock, liming and flooding treatments and their interactions were significant on soil pH and larval survival ( P < 0.05). Larval survival decreased from 80% to 60% with increasing soil pH from 4.8 to 5.7. Total larval weight per seedling decreased significantly from 0.060 g to 0.012 g when the soil pH increased from 5.1 to 5.7. Flooding reduced larval survival and growth, and increasing acidic soil pH by 1 unit would be an option for controlling soil acidity and for promoting integrated management of Diaprepes root weevil in citrus.

WATER STRESS AND ROOT INJURY FROM SIMULATED FLOODING AND DIAPREPES ABBREVIATUS ROOT WEEVIL LARVAL FEEDING IN CITRUS

Environmental stress from flooding can occur simultaneously with root weevil infestation to damage plant root systems. We conducted two factorial studies of flooding duration and Diaprepes abbreviatus (L.) root weevil larval feeding injury on citrus in the greenhouse in 2002 and 2003. Our objectives were to investigate the effect of soil anoxia by simulated flooding on plant water stress and the impact of prior flooding on root susceptibility to subsequent larval weevil feeding. The treatments consisted of two rootstock varieties, Swingle citrumelo [SWI; Citrus paradisi Macfad x Poncirus trifoliata (L.) Raf.] and Smooth Flat Seville (SFS; Citrus aurantium L.), flooding durations of 0, 10, 20, 30, or 40 days, and Diaprepes larval infestations of 0 and 5 neonates per seedling for 40 days. We used a Candler sand with 8 replicates in Experiment I and a Floridana loam with 15 replicates in Experiment II. Treatments were arranged in a completely ramdomized design. Plants were flooded, drained for a week, and then 1-day-old neonate larvae were introduced onto the soil surface of each seedling. Flooding significantly reduced soil redox potential (E h ), leaf stomatal conductance (g s ), and shoot growth (P < 0.05). Soil E h decreased from +220 to -100 mV within 1-3 days after flooding, and leaf g s declined from 260 to 80 mmol m -2 s -1 within 20 days of flooding. Flood-injured and larval-injured roots had little growth. With equal previous flooding durations (20 days), the larval survival was on average 25% higher in sandy soil than in loamy soil. Twenty-day prior flooded roots were more water stressed and also more susceptible to Diaprepes larval feeding injury. It is suggested that limited soil waterlogging and early root weevil larval control would be useful for plant protection.

Laranjeiras 'Valência' enxertadas em híbridos de trifoliata

O limão Cravo é o principal porta-enxerto da citricultura paulista. Sua suscetibilidade ao declínio dos citros e à gomose de Phytophthora reduz a produtividade, onera os tratos culturais e as colheitas e encurta a vida útil dos pomares. É necessário selecionar outros porta-enxertos tolerantes ou resistentes aos fatores bióticos e abióticos limitantes à citricultura paulista. Procuram-se também porta-enxertos nanicantes visando maior produtividade por área, aumento da eficiência e redução nos custos das inspeções e dos controles de pragas e doenças e nas colheitas. Os estudos vem se concentrando na seleção de clones e de híbridos de trifoliata. Laranjeiras 'Valência' enxertadas em híbridos de trifoliata produzidos no USDA foram plantadas em 1986 em Latossolo Vermelho-Amarelo, no município de Pirassununga, SP, próximo a pomares afetados pelo declínio dos citros e conduzidas sem irrigação. Nas oito primeiras colheitas os citrandarins Changsha ×English Small e Sunki × Benecke proporcionaram, em média, as maiores produções em frutos e em sólidos solúveis por planta. As menores produções foram obtidas com os citranges Carrizo e Troyer tetraplóides. A tangerina Miaray e o híbrido Smooth Flat Seville ´ citrumelo Swingle mostraram ser intolerantes à tristeza dos citros.

Citrus Rootstock Usage, Characteristics, and Selection in the Florida Indian River Region

Sour orange (Citrus aurantium) has been the dominant citrus rootstock in the Indian River region of Florida since the initial plantings in the 1880s. Use of this rootstock in new plantings has been rare since 1990 because of heightened concern about decline strains of citrus tristeza virus (CTV), to which this rootstock is highly susceptible. Because the proportion of trees remaining on sour orange rootstock and the rate of decline among them are important in predicting the economic consequences for the Indian River citrus industry, two surveys of rootstock usage were conducted for citrus in this growing region. In the first survey, growers were asked about rootstock usage and problems observed across all types of citrus, and responses represented 35% of acreage. In the second survey, growers were restricted to rootstock usage and grower observations on decline for grapefruit (C. paradisi), and responses represented 53% of acreage. Even though 44% of all current Indian River grove area has been planted since 1987, when use of sour orange for new plantings largely ceased, 48% of all citrus and 55% of all grapefruit grove area are currently on sour orange rootstock. The percentage of grapefruit trees on sour orange rootstock that showed significantly health decline in 2000 was 8% based on grower reports. The other root-stocks representing substantial commercial grove area have known problems and limitations that are likely to prevent any of them from gaining the prominence once held by sour orange. Swingle citrumelo (C. paradisi × Poncirus trifoliata) at about 25% of grove area, Cleopatra mandarin (Citrus reticulata) at about 8%, and Smooth Flat Seville (Citrus hybrid) at about 3% all represented similar acreage for grapefruit and across all cultivars, while Carrizo citrange (C. sinensis × P. trifoliata) use was reported for 4% of grapefruit and 13% overall. Evaluation and development of new rootstocks is vitally important for the Indian River area, especially for soils with significant clay and calcium content.

Evaluation of Recently Selected Mild Isolates of Citrus tristeza virus for Cross Protection of Hamlin Sweet Orange on Smooth Flat Seville Rootstock

Evaluation of Recently Selected Mild Isolates of Citrus tristeza virus for Cross Protection of Hamlin Sweet Orange on Smooth Flat Seville Rootstock

595 Computer Root Image Analysis of Citrus Rootstock Seedlings

Florida citrus has had an average annual on-tree-value of ≈1 billion dollars during the past decade in Florida. Nearly all of the 845,260 acres of citrus in Florida is produced on grafted trees consisting of a commercial scion cultivar and a rootstock selected specifically for local soil, environment, and pest pressures. With vastly different root-zone environments, ranging from deep sands to drained and cleared pine Flatwoods, a large number of different rootstocks are utilized. These rootstocks are started from seed at more than 100 commercial nurseries statewide, which currently produce an estimated 6 million trees a year. Although the optimum germination conditions, basic physiological performance, and adaptability of many rootstocks are known, there has been minimal investigation on early root development in seedling trays at the nursery. Four hundred seedlings of `Swingle' citrumelo (Citrus paradisi Macf. `Dunacn' × Poncirus trifoliata), `Smooth Flat Seville', `Volkamer' lemon (Citrus volkameriana), and `Sun Chu Sha' mandarin were seeded in a randomized block experimental design and grown at a commercial nursery. Seedling root systems (100/rootstock) were analyzed for a number of variables using the Rhizo (Regent Instruments, Inc.) software package and a dual light source scanner. Using the SAS general linear model procedure, hypothesis testing revealed rootstock selection had a significant effect on total root length, total root surface area, total root volume, number of root tips, number of root forks, root dry weight, and stem diameter. For most characteristics, rootstock genotype accounted for a greater portion of variability than samples (plant to plant variability).

Performance of `Hamlin' Orange on 16 Rootstocks in East-central Florida

`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.

732 PB 504 JUICE QUALITY FROM YOUNG TREES OF 6 VALENCIA CLONES ON 16 ROOTSTOCKS

Juice quality from 4-year-old `Valencia' sweetorange (C. sinensis (L.) Osbeck) nucellar seedling clones VS-F-55-28-X-E, VS-SPB-1-14-19-X-E, old-line clones V-10-12-7-X-E, V-51-3-3-(STG-64G-4)-X-E, and `Rohde Red Valencia' RRV-472-3-26-(STG-31-18)-X-E, RRV-472-11-43-(STG-19-2)-X-E were compared for percentage juice per fruit, “Brix, acid, °Brix/acid ratio, soluble solids per standard 40.9 kg field box, and juice color score. Rootstocks were sour orange, Smooth Flat Seville, Cleopatra mandarin, Sun Chu Sha, calamandarin, Valencia seedling, P. myoliare × Ridge Pineapple X73-26, Duncan grapefruit, Carrizo, Benton and C-35 citranges, Swingle and F-80-18 citrumelos, Rangpur lime × Troyer citrange, P. trifoliata, and Vangasay lemon. V-10-12-7 had the most juice. RRV-472-11-43 had less acid than the other clones. VS-SPB-1-4-19 had highest ratio and RRV-472-3-26 the lowest. Soluble solids per box were lowest for RRV-472-3-26. Juice color score was highest for the two `Rohde Red Valencia' clones and lowest for V-10-12-7. Rootstock affected all juice quality factors except juice color score.

Eight New Somatic Hybrid Citrus Rootstocks with Potential for Improved Disease Resistance

Protoplast culture following polyethylene glycol-induced fusion resulted in the regeneration of vigorous tetraploid somatic hybrid plants from eight complementary parental rootstock combinations: Citrus reticulata Blanco (Cleopatra mandarin) + C. aurantium L. (sour orange), C. reticulata (Cleopatra mandarin) + C. jambhiri Lush (rough lemon), C. reticulata (Cleopatra mandarin) + C. volkameriana Ten. &amp; Pasq. (Volkamer lemon), C. reticulata (Cleopatra mandarin) + C. limonia Osb. (Rang-pur), C. sinensis (L.) Osb. (Hamlin sweet orange) + C. limonia (Rangpur), C. aurantium (sour orange) + C. volkameriana (Volkamer lemon) zygotic seedling, C. auruntium hybrid (Smooth Flat Seville) + C. jambhiri (rough lemon), and C. sinensis (Valencia sweet orange) + Carrizo citrange [C. paradisi Macf. × Poncirus trifoliata (L.) Raf.]. Diploid plants were regenerated from nonfused callus-derived protoplasts of Valencia sweet orange and Smooth Flat Seville and from nonfused leaf protoplasts of sour orange, Rangpur, rough lemon, and Volkamer lemon. Regenerated plants were classified according to leaf morphology, chromosome number, and leaf isozyme profiles. All somatic hybrid plants were tetraploid (2n = 4× = 36). One autotetraploid plant of the Volkamer lemon zygotic was recovered, apparently resulting from a homokaryotic fusion. These eight new citrus somatic hybrids have been propagated and entered into field trials.

INJURY TO 27 CITRUS CULTIVARS ON 22 ROOTSTOCKS AT ONE-YEAR-OLD EXPERIENCING MINIMUM TEMPERATURE OF -4.4C

Evaluation ratings of cold injury following a freeze on December 24 &amp; 25, 1989, showed differences among scion cultivars and rootstock. `Star Ruby' grapefruit (Citrus paradisi Macf.) and `Fallglo' citrus hybrid, a cross of Bower mandarin citrus hybrid × Temple tangor (C. temple Hort. ex Y. Tanaka) were the most severely damaged scion cultivars. `Rohde Red' valencia orange selection 472-11-43. [C. sinensis (L.) Osbeck]. was the least damaged scion cultivar. Scions budded to Cleopatra mandarin (C. reshni Hort. ex Tan.) and FL 80-18 citrumelo [C. paradisi × Poncirus trifoliata (L.) Raf.] rootstock were damaged more than on other rootstock. Scions budded to smooth flat seville (C. aurantium?) and P. trifoliata × Ridge pineapple sweet orange selection 1573-26 [C. sinensis (L.) Osbeck] had the least injury. Analysis comparing replications showed the greatest damage to be in the north side of the planting.

Citrus Rootstocks and Their On-Site Evaluation

What rootstock to plant? That's an ever-present and always challenging question. In conversations with growers, this question is asked frequently because of problems with Swingle citrumelo, continued loss of trees on sour orange, and low solids for grapefruit grown on Smooth Flat Seville. This document is HS949, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and AgriculturalSciences, University of Florida. Publication date: August 2003.&#x0D; https://edis.ifas.ufl.edu/hs196