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

2016 ◽  
Vol 26 (6) ◽  
pp. 839-845
Author(s):  
Ed Stover ◽  
Youjian Lin ◽  
Xiaoe Yang ◽  
Tripti Vashisth
Keyword(s):  
Sweet Orange ◽  
South Florida ◽  
Poncirus Trifoliata ◽  
Colletotrichum Acutatum ◽  
Sour Orange ◽  
Citrus Paradisi ◽  
Mature Trees ◽  
Hydrogen Cyanamide ◽  
Florida Citrus ◽  
Citrus Macrophylla

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.

scholarly journals Rootstocks Affect Tree Growth, Yield, and Juice Quality of ‘Marsh’ Grapefruit

HortScience ◽  
2011 ◽  
Vol 46 (6) ◽  
pp. 841-848 ◽  
Author(s):  
William S. Castle ◽  
Kim D. Bowman ◽  
James C. Baldwin ◽  
Jude W. Grosser ◽  
Frederick G. Gmitter
Keyword(s):  
Growth Yield ◽  
Tree Height ◽  
Poncirus Trifoliata ◽  
Soluble Solids ◽  
Quality Data ◽  
Juice Quality ◽  
Sour Orange ◽  
Citrus Paradisi ◽  
High Productivity ◽  
River Region

Two adjacent rootstock trials were conducted in the east coast Indian River region of Florida with ‘Marsh’ grapefruit (Citrus paradisi Macf.) scion. The objective was to find rootstocks to replace sour orange (C. aurantium L.) because of losses to citrus tristeza virus, and to replace Swingle citrumelo [C. paradisi × Poncirus trifoliata (L.) Raf.] because of its limited usefulness in certain poorly drained coastal sites. The trials were conducted in randomized complete blocks with 12 single-tree replicates spaced 4.6 × 6.9 m. The soils were of the Wabasso and Riviera series. The first trial consisted largely of trees on citrange [C. sinensis (L.) Osb. × P. trifoliata] and citrumelo rootstocks, ‘Cipo’ sweet orange (C. sinensis), and various hybrid rootstocks. The second trial involved mandarin rootstocks (C. reticulata Blanco) and sour orange and related rootstocks. Trees were grown for 7 years and yield and juice quality data were collected for the last 4 years of that period. Those rootstocks identified as the most promising, based on combinations of smaller tree size and high productivity and juice quality, were two Sunki mandarin × Swingle trifoliate orange (TF) hybrids (C-54, C-146), a Sunki mandarin × Flying Dragon TF hybrid, C-35 citrange, and a Cleopatra mandarin × Rubidoux TF hybrid (×639). The trees on these five rootstocks cropped well leading to soluble solids (SS) values of 3000 to 4000 kg/ha when they were 7-years old. The trees on C-54 and C-146 were relatively large, somewhat taller than trees on sour orange, whereas those on C-35 and the Sunki × Flying Dragon hybrid were smaller and similar to sour orange in tree height. Fruit quality among the trees on C-35 and the Sunki × Flying Dragon hybrid had relatively high SS concentration (better than sour orange), and the other three rootstocks had relatively lower solids concentration (poorer than sour orange). The trees on C-35 and the Sunki × Flying Dragon hybrid would be good candidates for higher density orchards.

scholarly journals Performance of ‘Valencia’ Sweet Orange Trees on 12 Rootstocks at Two Locations and an Economic Interpretation as a Basis for Rootstock Selection

HortScience ◽  
2010 ◽  
Vol 45 (4) ◽  
pp. 523-533 ◽  
Author(s):  
William S. Castle ◽  
James C. Baldwin ◽  
Ronald P. Muraro ◽  
Ramon Littell
Keyword(s):  
Financial Analysis ◽  
Sweet Orange ◽  
Poncirus Trifoliata ◽  
Soluble Solids ◽  
Juice Quality ◽  
Sour Orange ◽  
Central Florida ◽  
Carrizo Citrange ◽  
Acid Ratio ◽  
Fruit Samples

Two field experiments with ‘Valencia’ sweet orange [Citrus sinensis (L.) Osb.] trees propagated on 12 rootstocks were conducted in commercial orchards. The objectives were to compare rootstock horticultural performance between two locations with soils representative of the Central Florida Ridge (AP) and coastal flatwoods (I), the major citrus-growing regions in Florida, and to see if financial analysis would provide an improved basis for interpreting rootstock performance. The randomized complete-block trials involved six-tree plots replicated eight or 10 times at planting densities of 358 trees (AP) or 252 trees (I)/ha, respectively. Tree growth and survival, yield, and juice quality were measured for 15 years. When losses occurred, trees were replaced annually with another one on the same rootstock. The data of seven rootstocks were subjected to a financial interpretation of three scenarios: tree loss and tree loss with or without tree replacement using the discounted cash flow and internal rate of return methods at a 15% rate. At the flatwoods location, when differences among replications became apparent on several rootstocks, soil data were collected to study its possible association to tree performance; also in this trial, 400-kg fruit samples were differentially harvested in 2 successive years from mature trees on each of five commercial rootstocks when the juice soluble solids/acid ratio was near 15. The juice was extracted, pasteurized, and evaluated for flavor by an experienced taste panel. The horticultural data obtained for trees on specific well-studied rootstocks [Volkamer (C. volkameriana Ten. & Pasq.)] and rough (C. jambhiri Lush.) lemons, Carrizo citrange [C. sinensis × Poncirus trifoliata (L.)], sour orange [C. aurantium (L.)], Cleopatra mandarin (C. reshni Hort. ex Tan.), trifoliate orange (P. trifoliata), a selection of sweet orange (C. sinensis), and Swingle citrumelo (C. paradisi Macf. × P. trifoliata) at both locations were typical of their well-documented performance in Florida and elsewhere. Tree losses were virtually only from citrus blight and ranged from none (sour orange) to greater than 50% (Volkamer and rough lemons) at both locations, although tree loss began later at the Central Florida location. ‘Valencia’ cuttings (only at the flatwoods site) were long-lived and cropped well for their smaller size compared with the budded trees. Taste panelists were not able to distinguish differences over two seasons among pasteurized ‘Valencia’ juices produced from trees on different rootstocks and normalized by soluble solids/acid ratio. Yield and planting density were the main factors affecting financial outcome; also, in the highly variable soils of the coastal flatwoods, trees growing in sites with greater depth to an argillic layer had 30% to 200% higher yields. Trees on Volkamer lemon had only ≈50% survival at both locations but had the highest ($7,338/ha I) or one of the highest cash flows ($13,464/ha AP) as compared with one of the commercial standards, Carrizo citrange ($6,928 I; $16,826 AP), which had only ≈25% tree loss. Inclusion of financial analysis, with certain limitations, was concluded to considerably improve rootstock selection decisions compared with selection based only on horticultural data.

scholarly journals Production of interstocked 'Pera' sweet orange nursey trees on 'Volkamer' lemon and 'Swingle' citrumelo rootstocks

2006 ◽  
Vol 63 (1) ◽  
pp. 5-10 ◽  
Author(s):  
Eduardo Augusto Girardi ◽  
Francisco de Assis Alves Mourão Filho
Keyword(s):  
Citrus Sinensis ◽  
Sweet Orange ◽  
Dry Weight ◽  
Poncirus Trifoliata ◽  
Production Cycle ◽  
Citrus Paradisi ◽  
Higher Plant ◽  
Weight Percentage ◽  
Volkamer Lemon ◽  
Swingle Citrumelo

Incompatibility among certain citrus scion and rootstock cultivars can be avoided through interstocking. 'Pera' sweet orange (Citrus sinensis L. Osbeck) nursery tree production was evaluated on 'Swingle' citrumelo (Poncirus trifoliata (L.) Raf x Citrus paradisi Macf) and 'Volkamer' lemon (Citrus volkameriana Pasquale) incompatible rootstocks, using 'Valencia' and 'Hamlin' sweet oranges (Citrus sinensis L. Osbeck), 'Sunki' mandarin (Citrus sunki Hort. ex Tanaka), and 'Cleopatra' mandarin (Citrus reshni Hort. ex Tanaka) as interstocks. Citrus nursery trees interstocked with 'Pera' sweet orange on both rootstocks were used as control. 'Swingle' citrumelo led to the highest interstock bud take percentage, the greatest interstock height and rootstock diameter, as well as the highest scion and root system dry weight. Percentage of 'Pera' sweet orange dormant bud eye was greater for plants budded on 'Sunki' mandarin than those budded on 'Valencia' sweet orange. No symptoms of incompatibility were observed among any combinations of rootstocks, interstocks and scion. Production cycle can take up to 17 months with higher plant discard.

scholarly journals A GENETIC MAP OF CITRUS BASED ON ISOZYMES AND RFLPS.

HortScience ◽  
1990 ◽  
Vol 25 (9) ◽  
pp. 1154b-1154 ◽  
Author(s):  
David C. Jarrell ◽  
Mikeal L. Roose
Keyword(s):  
Genetic Map ◽  
Sweet Orange ◽  
Poncirus Trifoliata ◽  
Citrus Paradisi ◽  
Structural Rearrangements ◽  
Mendelian Segregation ◽  
Dna Libraries ◽  
Citrus Rootstock ◽  
Multipoint Linkage ◽  
Segregating Population

We report a preliminary genetic map of citrus based on segregation of 8 isozyme and at least 33 RFLP loci. The segregating population consisted of 60 plants from a cross of two citrus rootstock, `Sacaton' citrumelo × `Troyer' citrange. This cross represents an intergeneric F2 since `Sacaton' is Citrus paradisi (grapefruit) × Poncirus trifoliata (trifoliate orange) and `Troyer' is C. sinensis (sweet orange) × P. trifoliata. RFLPs were identified using anonymous probes from both cDNA and genomic DNA libraries of citrus. About 20% of the loci deviated significantly from Mendelian segregation. Two-point linkage analysis identified 8 linkage groups in which pairs of loci were within 30 centimorgans. This suggests that we have markers on most of the 9 chromosomes of Citrus. A map based on multipoint linkage estimates will be reported. Evidence for structural rearrangements between Citrus and Poncirus and extension of the map to additional marker and disease resistance loci will be discussed.

scholarly journals 080 Genetic Transformation of Grapefruit (Citrus paradisi) and Sweet Orange (C. sinensis) With the Coat Protein Gene of CTV

HortScience ◽  
2000 ◽  
Vol 35 (3) ◽  
pp. 402C-402
Author(s):  
Elvia C. Palacios-Torres ◽  
M. Alejandra Gutièrrez-Espinosa ◽  
Gloria A. Moore ◽  
Gustavo Mora-Aguilera ◽  
Daniel L. Ochoa-Martínez ◽  
...  
Keyword(s):  
Coat Protein ◽  
Coat Protein Gene ◽  
Protein Gene ◽  
Sweet Orange ◽  
Viral Gene ◽  
Sour Orange ◽  
Citrus Paradisi ◽  
Etiolated Seedlings ◽  
Selection Medium ◽  
Citrus Tristeza Closterovirus

Citrus Tristeza Closterovirus (CTV) induces mild and/or severe symptoms on Citrus species. It may cause death of trees if the rootstock-scion combination is susceptible. It has been found in other plant/virus combinations that transformation with partial or complete viral genes (e.g., coat protein genes) can confer resistance to the resulting transgenic plants. We previously reported A. tumefaciens mediated transformation and production of two sour orange (C. aurantium L.) plants expressing the coat protein gene of CTV, which was the first report of production of transgenic Citrus using a viral gene. However, in order to properly evaluate resistance, it is necessary to obtain as many transgenic Citrus plants from single transformation events as possible. Therefore, we are currently transforming grapefruit (Citrus paradisi) `Marsh' and `Star Ruby' and sweet orange (C. sinensis) `Valencia' with CTV coat protein genes. These species are susceptible to CTV and more amenable to transformation than sour orange. Epicotyl segments of etiolated seedlings were inoculated with A. tumefaciens strain EHA101 harboring binary plasmid pGA482GG containing the coat protein gene of mild Florida CTV strain T30 (CP-T30) or severe Florida strain T36 (CP-T36). Putatively transformed shoots were regenerated on selection medium containing kanamycin. Regenerated shoots were evaluated with GUS assays; those shoots positively identified by GUS were then evaluated with PCR. We have currently identified 17 `Marsh' grapefruit, 20 `Star Ruby' grapefruit, and seven sweet orange putatively transformed plants.

scholarly journals Dynamics of ‘Candidatus Liberibacter asiaticus’ Colonization of New Growth of Citrus

2018 ◽  
Vol 108 (10) ◽  
pp. 1165-1171 ◽  
Author(s):  
Mark E. Hilf ◽  
Weiqi Luo
Keyword(s):  
Population Growth ◽  
Bacterial Population ◽  
Sweet Orange ◽  
Adventitious Shoots ◽  
Bacterial Pathogen ◽  
Sour Orange ◽  
Candidatus Liberibacter Asiaticus ◽  
Candidatus Liberibacter ◽  
Liberibacter Asiaticus ◽  
Citrus Macrophylla

‘Candidatus Liberibacter asiaticus’ is a phloem-colonizing intracellular bacterial pathogen of citrus associated with the disease huanglongbing. A study of patterns of colonization and bacterial population growth in new growth of different citrus types was conducted by pruning infected citron, sweet orange, sour orange, mandarin, citrange, and Citrus macrophylla trees to force the growth of axillary and adventitious shoots. The first three leaves on newly emerged shoots were collected at 30, 60, and 90 days to assess colonization and population growth of ‘Ca. L. asiaticus’ using real time PCR (qPCR). Single trials were conducted with mandarin and citron, two trials each for citrange, sour orange and sweet orange, and four trials for C. macrophylla. In citron the proportion of colonized leaves increased significantly over time, with 67, 85, and 96% of leaves colonized at 30, 60, and 90 days, respectively. For the other citrus types, the exact proportion of colonized leaves differed, but colonization exceeded 60% in mandarin, sour orange, and citrange, and exceeded 80% at 30 days in two trials with sweet orange and three trials with C. macrophylla, but there was no significant increase in the proportion of colonized leaves at 60 and 90 days. Bacteria were readily detected by 30 days in new leaves of all citrus types. Differences in the growth of the bacterial population between citrus types and at different times of the year were noted, but common trends were apparent. In general, bacterial titers peaked at 60 days, except in leaves of C. macrophylla where bacterial titers peaked at 30 days. The early and consistently high proportion of leaf colonization observed for new growth of sweet orange during two trials and for C. macrophylla during three trials indicates a near synchronous colonization of new leaves by 30 days.

scholarly journals Huanglongbing-related Responses of ‘Valencia’ Sweet Orange on Eight Citrus Rootstocks during Greenhouse Trials

2018 ◽  
Vol 28 (6) ◽  
pp. 776-782 ◽  
Author(s):  
Ed Stover ◽  
David G. Hall ◽  
Jude Grosser ◽  
Barrett Gruber ◽  
Gloria A. Moore
Keyword(s):  
Somatic Hybrids ◽  
Sweet Orange ◽  
Growth Parameters ◽  
Economic Benefits ◽  
Poncirus Trifoliata ◽  
Percentage Increase ◽  
Sour Orange ◽  
Trunk Diameter ◽  
Rough Lemon ◽  
The Impact

The primary objective of this experiment was to determine if the selection of rootstock (Citrus and hybrids) could enhance the development of huanglongbing (HLB)-related symptoms associated with the pathogen Candidatus Liberibacter asiaticus (CLas) in sweet orange (Citrus sinensis). If so, then it may permit more rapid identification of HLB-susceptible compared to HLB-resistant scion types. The secondary objective was to assess the impact of different rootstocks on plant growth parameters and health to determine if trees on any rootstocks displayed reduced sensitivity to HLB-influenced growth restriction. ‘Valencia’ sweet orange was budded on each of the following eight genotypes: Carrizo (C. sinensis × Poncirus trifoliata); Cleopatra (C. reshni); Green-7 {a complex allotetraploid from somatic hybrids [C. clementina × (C. paradisi × C. reticulata) + C. grandis] × [(C. aurantium + (C. sinensis × P. trifoliata)]}; UFR-2 (a complex allotetraploid from somatic hybrids {[C. clementina × (C. paradisi × C. reticulata)] + C. grandis} × (C. reticulata + P. trifoliata)); UFR-4 (same pedigree as UFR-2); rough lemon (C. jambhiri); sour orange (C. aurantium); and US-897 (C. reticulata × P. trifoliata). Half of the trees on each rootstock were bud-inoculated with CLas and half were inoculated with the asian citrus psyllid [ACP (Diaphorina citri)], which is the CLas vector. During both experiments, no rootstock conferred significantly greater HLB symptom severity compared to trees on Carrizo; however, trees on several rootstocks had reduced HLB severity compared to those on Carrizo. Regarding the bud-inoculated trees after 3 years, trees on UFR-4 displayed greater overall health than trees on Carrizo, Green-7, sour orange, and US897, and trees on UFR-4 had a higher percentage of plants with leaf cycle threshold (Ct) values >36 compared with trees on Cleopatra and rough lemon (62 vs. 26-29 respectively). Regarding the ACP-inoculated trees after 3 years, trees on UFR-4 had better overall health than trees on Carrizo, rough lemon, and US-897, and trees on sour orange had a higher percentage of plants with leaf Ct values greater than 36 only compared to Cleopatra and US-897. The percentage increase in the trunk diameter per month over the course of each entire experiment was significantly greater for UFR-2 in both trials than all rootstocks except UFR-4. Only root CLas titers were sometimes significantly higher for trees on other rootstocks compared to those on Carrizo. Although no rootstock provided acceleration of HLB symptom development compared with Carrizo, some rootstocks conferred significantly greater health compared to Carrizo. However, it is uncertain whether the modest differences in health and growth observed in these greenhouse trials would translate to economic benefits in the field.

scholarly journals Trunk Xylem Anatomy of Mature Healthy and Blighted Grapefruit Trees on Several Rootstocks

1994 ◽  
Vol 119 (2) ◽  
pp. 185-194 ◽  
Author(s):  
Luiz A.B.C. Vasconcellos ◽  
William S. Castle
Keyword(s):  
Cross Sections ◽  
Citrus Tristeza Virus ◽  
Poncirus Trifoliata ◽  
Vessel Element ◽  
Sour Orange ◽  
Citrus Paradisi ◽  
Xylem Anatomy ◽  
Rough Lemon ◽  
Tristeza Virus ◽  
Cleopatra Mandarin

Wood samples were taken from healthy and blighted citrus trees on several rootstocks to describe and compare the xylem anatomy of the healthy trees and to determine if blight altered xylogenesis. Horizontal trunk xylem cores, 6 cm long, were extracted from blighted 18-year-old commercial grapefruit (Citrus paradisi Macf.) trees on rough lemon (RL) (C. jambhiri Lush.), Cleopatra mandarin (CM) (C. reshni Hort. ex Tan.), and Carrizo citrange (CC) [C. sinensis (L). Osb. × Poncirus trifoliata (L.) Raf] and from healthy trees on those rootstocks and sour orange (SO) (C. aurantium L.). Cores were taken from the eastern and western sides of the scion and rootstock of each tree. The cores were divided into 2-cm pieces and cross-sections were prepared for analysis of vessel element (VE) number and diameter in 0.5-cm increments. A sample-size study showed that tree side was not a significant source of variation and that 10 replications were sufficient to detect differences of ≈12% from the overall mean. Among the healthy trees, VE densities and diameters were similar for the trees on CC or RL and larger than those for trees on SO or CM. VEs were generally smaller and at lower densities in the scion than the rootstock. Few VE occlusions were observed in the healthy trees. In the blighted trees, to a depth of 1 cm, VE density increased and diameter decreased compared to the healthy trees. The largest change occurred in the trees on RL and in the rootstock vs. scion trunk part. The frequency of VE amorphous plugs in blighted trees ranged from 1% to 30%. Similar changes in xylem anatomy were not found in trees with citrus tristeza virus or soilborne pests. Trunk water uptake and dye movement patterns in blighted trees were typical for trees with xylem dysfunction.

scholarly journals Effects of Insecticides on Asian Citrus Psyllid (Hemiptera: Psyllidae) Populations in a Florida Citrus Grove

2007 ◽  
Vol 8 (1) ◽  
pp. 6 ◽  
Author(s):  
Charles A. Powell ◽  
Michael S. Burton ◽  
Robert A. Pelosi ◽  
Mark A. Ritenour ◽  
Robert C. Bullock
Keyword(s):  
Sweet Orange ◽  
Block Design ◽  
Insect Control ◽  
Asian Citrus Psyllid ◽  
Sour Orange ◽  
Diaphorina Citri ◽  
Citrus Grove ◽  
Randomized Complete Block Design ◽  
Florida Citrus ◽  
Insecticide Control

Asian citrus psyllid, Diaphorina citri Kuwayama, populations were monitored in a ‘Valencia’ sweet orange on sour orange rootstock plot planted in 1997. The plot was scouted weekly and the number of psyllids, percent trees infested, and the percentage of flush infested per tree were recorded over a 3-year period. The plot was treated with 7 insect control treatments: Admire (imidacloprid) applied at 12-, 6-, 3-, or 2-month intervals; Temik applied annually; Meta-Systox R applied annually; or no insecticide control using a randomized complete block design. Psyllid infestations persisted throughout the year. The lowest populations occurred during the winter (November-January) with peaks in the spring and fall. Annual applications of Temik, Meta-Systox R, or Admire did not reduce psyllid populations. Biannual or more frequent applications of Admire significantly reduced psyllid numbers, percentage of trees with psyllid infestations, and the percentage of flushes infested with psyllids. Accepted for publication 29 August 2007. Published 1 November 2007.

scholarly journals Detection and Characterization of a New Strain of Citrus Canker Bacteria from Key/Mexican Lime and Alemow in South Florida

Plant Disease ◽  
2004 ◽  
Vol 88 (11) ◽  
pp. 1179-1188 ◽  
Author(s):  
Xiaoan Sun ◽  
Robert E. Stall ◽  
Jeffrey B. Jones ◽  
Jaime Cubero ◽  
Tim R. Gottwald ◽  
...  
Keyword(s):  
Sweet Orange ◽  
Agar Plate ◽  
Lima Bean ◽  
Citrus Canker ◽  
Fatty Acid Analysis ◽  
South Florida ◽  
Poncirus Trifoliata ◽  
Enzyme Linked Immunosorbent Assay ◽  
Mexican Lime ◽  
Dna Reassociation

In the Wellington and Lake Worth areas of Palm Beach County, FL, citrus canker appeared on Key/Mexican lime (Citrus aurantiifolia) and alemow (C. macrophylla) trees over a period of about 6 to 7 years before detection, but nearby canker-susceptible citrus, such as grapefruit (C. × paradisi) and sweet orange (C. sinensis), were unaffected. Colonies of the causal bacterium, isolated from leaf, stem, and fruit lesions, appeared similar to the Asiatic group of strains of Xanthomonas axonopodis pv. citri (Xac-A) on the nutrient agar plate, but the growth on lima bean agar slants was less mucoid. The bacterium produced erumpent, pustule-like lesions of typical Asiatic citrus canker syndrome after inoculation into Key/Mexican lime, but brownish, flat, and necrotic lesions on the leaves of Duncan grapefruit, Madame Vinous sweet orange, sour orange (C. aurantium), citron (C. medica), Orlando tangelo (C. reticulata × C. × paradisi), and trifoliate orange (Poncirus trifoliata). The bacterium did not react with the Xac-A specific monoclonal antibody A1 using enzyme-linked immunosorbent assay (ELISA) and could not be detected by polymerase chain reaction (PCR)-based assays using primers selected for Xac-A. DNA reassociation analysis confirmed that the pathogen, designated as Xac-AW, was more closely related to Xac-A and Xac-A* strains than X. axonopodis pv. aurantifolii or the citrus bacterial spot pathogen (X. axonopodis pv. citrumelo). The strain can be easily differentiated from Xac-A and Xac-A* using ELISA, PCR-based tests, fatty acid analysis, pulsed-field gel electrophoresis of genomic DNA, and host specificity.

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