Progress 02/01/13 to 09/30/17
Outputs
Target Audience:Citrus canker researchers worldwide and Florida citrus growers managing citrus canker Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?Publications on canker control distibuted to Florida citrus growers What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Antimicrobial activity of experimental formulations of two structurally different nano-zinc oxide materials, plate-like Zinkicide SG4 and particulate Zinkicide SG6, was evaluated against Xanthomonas citri subsp.citri, the cause of citrus canker. In vitro assay demonstrated Zinkicide SG4 had a twofold lower minimum inhibitory concentration (MIC) against Escherichia coli and X. alfalfae subsp. citrumelonis (62.5 to 250 mg/ml) compared with copper sulfate (250 mg/ml), copper hydroxide (250 to 500 mg/ml), or cuprous oxide/zinc oxide (125 to 250 mg/ml). Zinkicide SG6 had a sevenfold to eightfold lower MIC against Escherichia coli and X. alfalfae subsp. citrumelonis (31 to 250 mg/ml). Leaves of sweet orange (Citrus sinensis) and fruit of 'Ruby Red' grapefruit (C. paradisi) were evaluated for citrus canker disease control. A greenhouse assay with foliage demonstrated that spray treatment with Zinkicide reduced citrus canker lesion development after injection-infiltration of X. citri subsp. citri into the leaf intercellular space. In field trials conducted in Southeast Florida in 2014 and 2015, Zinkicide SG4 and SG6 reduction of grapefruit canker incidence exceeded that of cuprous oxide and cuprous oxide/zinc oxide bactericides. Zinkicide formulations were also effective against the fungal diseases, citrus scab (Elsinoe fawcetti) and melanose (Diaporthe citri), on grapefruit.No sign of phytotoxicity to the fruit rind was observed during either season. Antimicrobial activity of Zinkicide for protection of leaves and fruit against X. citri subsp. citri was comparable or exceeded that for commercial copper and zinc oxide formulations which may be attributed to translaminar movement of Zinkicide.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
Young M, Ozcan A, Myers ME, Johnson EG, Graham JH, Santra S. 2017 Multimodal generally recognized as safe ZnO/nanocopper composite: A novel antimicrobial material for the management of citrus phytopathogens. J. Agric. Food Chem. DOI: 10.1021/acs.jafc.7b025.
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Graham JH, Johnson EG, Myers ME, Young M, Rajasekaran P, Das S, Santra S. 2016. Potential of nano-formulated zinc oxide for control of citrus canker on grapefruit trees. Plant Dis. 100:2442-2447.
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Sena-V�lez M, Redondo C, Graham J H, Cubero J. 2016. Presence of extracellular DNA during biofilm formation by Xanthomonas citri subsp. citri strains with different host range.
PLOS ONE | DOI:10.1371/journal.pone.0156695
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Graham JH, Gerberich KM, Davis CL. 2016. Injection-infiltration of attached grapefruit with Xanthomonas citri subsp. citri to evaluate seasonal population dynamics in citrus canker lesions. J. Phytopath. 164: 528533.
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Graham JH, Brooks C, Yonce HD. 2016. Importance of early season copper sprays for protection of Hamlin orange fruit against citrus canker infection and premature fruit drop. Proc. Fla. State Hort. Soc. 129.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2016
Citation:
Graham JH, Myers ME, Gottwald TR, Bock CH. 2016. Effect of windbreaks on wind speed and canker incidence on grapefruit. Citrus Res. & Tech. 37: 173-181.
|
Progress 10/01/16 to 09/30/17
Outputs
Target Audience:Citrus canker researchers and Florida citrus growers Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
For fresh grapefruit, the goal is to maximize pack-out by minimizing canker lesions on fruit. The objective of these trials was to determine the relationship between wind speed and incidence and severity of citrus canker on 5 to 7 yr-old Ruby Red grapefruit trees located in two trial blocks (~4.5 ha) surrounded on all sides by a 6 to 10 m tall Corymbia torelliana windbreak. The experiment was conducted from 2013 to 2015. A series of weather stations were deployed in east-west and north-south directions across the orchards to measure the effect of proximity of citrus trees to the windbreak on wind speed expressed as the number of wind gusts ≥5 m s-1, and to determine the relationship with incidence of fruit lesions on grapefruit. The number of wind gusts ≥5 m s-1 increased with distance from the windbreak. The highest fruit canker incidence occurred in approximately the central zone of the block and the lowest incidence was found nearest windbreaks. Number of wind gusts and canker were linearly related, i.e., the greater the number of gusts, the higher the fruit disease. As the number of wind gusts increased with distance from the windbreak, incidence of unsightly wind scar also increased. These results confirm that windbreaks are a highly effective method for protection of fruit from infection by Xanthomonas citri subsp. citri, as well as physical damage from wind buffeting.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
Young M, Ozcan A, Myers ME, Johnson EG, Graham JH, Santra S. 2017 Multimodal generally recognized as safe ZnO/nanocopper composite: A novel antimicrobial material for the management of citrus phytopathogens. J. Agric. Food Chem. DOI: 10.1021/acs.jafc.7b025.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2016
Citation:
Graham JH, Myers ME, Gottwald TR, Bock CH. 2016. Effect of windbreaks on wind speed and canker incidence on grapefruit. Citrus Res. & Tech. 37: 173-181.
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Progress 10/01/15 to 09/30/16
Outputs
Target Audience:Citrus canker researchers worldwide and Florida citrus growers managing citrus canker Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?Presentation: Florida Citrus Growers Institute, "Reasons for Inconsistent Control of Citrus Canker", SWFCC, Avon Park, April 7, 2015 (300 growers) Publication:Dewdney M, Graham J2016.Foliar disease management 2016.Citrus Ind. 97(3):24-27. What do you plan to do during the next reporting period to accomplish the goals?There is also a need to develop more effective control of canker on newly established trees which are at the most susceptible stage of development because of the higher frequency of immature flush development compare to older trees. Prior to fruit bearing, young trees are not usually treated with copper for foliar/fruit disease control, so the objective is to minimize if not pre-empt the need for copper sprays to control canker on young orange trees. In the case of highly susceptible grapefruit more than one mode of action (contact and systemic) will probably be necessary to control disease until full establishment of windbreaks. The complementation and additive effects of contact and systemic activity for young grapefruit are being estimated in new plantings of highly susceptible grapefruit. More consistent reduction of foliar symptoms and canker-induced defoliation on young trees has been achieved with Admire and Platinum soil drenches applied at the beginning and during the growing season. Actigard as a soil drench is also efficacious but without the risk of non- target effects on insects and ground water Syngenta conducted an Experimental Use Program to evaluate the integration of Actigard with Copper sprays for canker control in grapefruit and early oranges with the intention of registering the product for use in canker management in Florida as well as in other crops. Our research results in Citrus trials were the impetus for Syngenta's EUP in the US. Actigard has received approval for a bearing label registration in 2016.
Impacts
What was accomplished under these goals?
Proper timing of copper sprays for protection of fruit from infection by Xanthomonas citri subsp. citri, the cause of citrus canker, is important because early season lesions induce premature fruit drop. The objective of the trials reported herein was to evaluate early season sprays of copper for control of fruit infection and drop in 3- to 5 year-old 'Hamlin' trees in a south central Florida citrus grove. Soluble and fixed copper formulations were applied with an airblast sprayer at 21-day intervals. In 2011, early season infection occurred due to periodic rains in late March and early April before the initiation of copper sprays. Subsequently, nine sprays of copper formulations from April to September only marginally reduced the incidence of fruit lesions compared to the untreated checks (UTC). Fruit drop ranged from 69% of the tree crop in the UTC to an average of 45% in the copper treatments. In 2012 in same location, five copper sprays of 5 year-old trees began before rains in March-April. Incidence of fruit lesions was substantially lower and fruit drop due to canker was 10 fold less than in 2011. In 2014, copper sprays of 3-year-old trees were initiated before below average March-April and above average May rainfall. In this season, incidence of fruit disease and fruit drop were very low. In 2015 in same location, copper sprays of 4-year-old trees were initiated before above average April and below average May rainfall and the incidence of fruit disease and fruit drop were significantly reduced by copper sprays. Timing of sprays in advance of rains in late March and early April is critical for protecting fruit from 0.5 to 1.0 cm (0.25 to 0.50 inches) in diameter. Inoculum in form of infected leaves and stems from the previous season is always present in the spring. Early fruit infection resulting in fruit drop depends on coincidence of March-April rains with the most susceptible fruit stage. In June-July, infections of fruit larger than 4.0 cm (1.5 inches) result in smaller lesions that do not induce fruit abscission and premature drop. For fresh grapefruit the goal is to maximize pack-out by minimizing canker lesions on fruit. The objective of these trials was to determine the relationship between wind speed and incidence and severity of citrus canker on 5 to 7 yr-old 'Ruby Red' grapefruit trees located in two trial blocks (~4.5 ha) surrounded on all sides by a 6 to 10 m tall Corymbia torelliana windbreak. The experiment was conducted from 2013 to 2015. A series of weather stations were deployed in east-west and north-south directions across the orchards to measure the effect of proximity of citrus trees to the windbreak on wind speed expressed as the number of wind gusts ≥18 km/h, and to determine the relationship with incidence of fruit lesions on grapefruit. The number of wind gusts ≥18 km/h increased with distance from the windbreak. The highest fruit canker incidence occurred in approximately the central zone of the block and the lowest incidence was found nearest windbreaks. Number of wind gusts and canker were linearly related, i.e., the greater the number of gusts, the higher the fruit disease. As the number of wind gusts increased with distance from the windbreak, incidence of unsightly wind scar also increased. These results confirm that windbreaks are a highly effective method for protection of fruit from infection by Xanthomonas citri subsp. citri, as well as physical damage from wind buffeting. To study population dynamics of Xanthomonas citri subsp. citri (Xcc) in citrus canker lesions on fruit, a needle-free injector was used for infiltration of bacterial inoculum into fruit in situ on mature 'Ruby Red' grapefruit (Citrus paradisi Macf.) trees in Florida. Inoculations of Xcc at 105 colony forming units (cfu) per ml were conducted in 2012 and 2013 on attached fruit varying from 15 mm to 90 mm in diameter. Inoculations were repeated every 2-3 weeks until the fruit were no longer injectable. On fruit less than 40 mm in size, erumpent lesions formed within 2 weeks of inoculation and expanded 1 to 9 mm in diameter from 30 to 120 days post inoculation (dpi). Xcc populations in lesions were 6 to 8 log cfu per lesion at 30 dpi and maintained this population up to 90 dpi. By 120 dpi, Xcc populations declined 1 to 3 log units as rainfall and temperature decreased in September-October. Xcc populations declined to ~3 log cfu per lesion after 120 dpi in November 2012 and 2013, whereas, the population resurged to 5 log cfu per lesion after 180 dpi in January-February 2014.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Sena-V�lez M, Redondo C, Graham J H, Cubero J. 2016. Presence of extracellular DNA during biofilm formation by Xanthomonas citri subsp. citri strains with different host range.
PLOS ONE | DOI:10.1371/journal.pone.0156695
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Graham JH, Gerberich KM, Davis CL. 2016. Injection-infiltration of attached grapefruit with Xanthomonas citri subsp. citri to evaluate seasonal population dynamics in citrus canker lesions. J. Phytopath. 164: 528533.
- Type:
Journal Articles
Status:
Awaiting Publication
Year Published:
2016
Citation:
Graham JH,Brooks C, Yonce HD. Importance of Early Season Copper Sprays for Protection of Hamlin Orange Fruit Against Citrus Canker Infection and Premature Fruit Drop. Proc. Florida State Hort. Soc.
- Type:
Conference Papers and Presentations
Status:
Under Review
Year Published:
2016
Citation:
Graham JH, Myers ME, Gottwald TR, Bock CH. Effect of windbreaks on wind speed and citrus canker incidence on grapefruit. International Citrus Congress 2016: Sustainable Agriculture: The Role of Applied Knowledge.
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Progress 10/01/14 to 09/30/15
Outputs
Target Audience:Citrus canker researchers worldwide and Florida citrus growers managing citrus canker Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Training for one postdoctoral researcher How have the results been disseminated to communities of interest?Florida citrus grower article in Citrus Industry magazine: Graham J, Bock, C. 2015. Reasons for inconsistent citrus canker control. Citrus Ind. 96(4):22-25. Florida Citrus Growers Institute, "Reasons for Inconsistent Control of Citrus Canker", SWFCC, Avon Park, April 7, 2015 (300 growers) Other effort: Member of USDA risk assessment team (RAT) for Harris (July 9, 2015) and Holmberg (October 15, 2015) to make recommendations for changes in protocols to prevent Xcc infestation for nursery stock permitted for shipment to non-citrus producing states. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Citrus Canker is a serious disease that affects production of almost all commercial citrus cultivars in subtropical citrus growing regions worldwide. The causal agent, Xanthomonas citri subsp. citri (Xcc), is classified as a quarantine pathogen in European Union (EU) which necessitates treatment of citrus fruit before entry into the EU marketing zone. In this study, the effectiveness of selected bactericides for leaf and fruit disinfection was evaluated. Bacterial aggregation and viability were assayed on abiotic or biotic surfaces in vitro and in planta after treatments with NaCl, CuSO4, NaClO, sodium orthophenylphenate and two hydrogen peroxide based compounds. Most of the bactericides at higher concentrations reduced biofilm formation and Xcc viability compared to the non-treated control, but did not completely prevent or remove biofilms or eradicate Xcc from either biotic or abiotic surfaces. Some of the bactericides at sub-lethal concentrations increased aggregates in which Xcc was viable. Based on these results, we conclude that exposure to the bactericides is variable depending on biofilm formation and that plant and fruit disinfection will not only require treatment with an effective bactericide to kill the bacterium but also include the biofilm disruption. Xanthomonas citri subsp. citri (Xcc) strain A is the causal agent of citrus canker on most Citrus spp. and close relatives. Two restricted host range strains, Aw and A*, from Florida and southwest Asia, respectively, infect Mexican lime. Several studies have linked biofilm formation by Xcc to bacterial colonization prior to and after plant ingress, but none have evaluated connections between biofilm formation and the behaviour of different strains of Xcc on citrus hosts and non-hosts. In this study biofilm formation and swimming motility were evaluated for citrus pathogenic xanthomonads including wide and restricted host range strains of Xcc, X. alfalfae subsp. citrumelonis (Xac) (the causal agent of citrus bacterial spot) and X. campestris pv. campestris (Xc). Differential biofilm formation was observed in vitro and in planta among the Xanthomonas strains assayed. Minimal medium XVM2 increased biofilm formation, especially for those strains with a host range restricted to Mexican lime. In planta, strains produced more biofilm on leaves or fruits of their host than on non-hosts. Scanning electron microscopy of biofilms on leaf and fruit surfaces revealed differences in structure of bacterial aggregates with respect to the strain's host range. In addition, swimming motility varied widely depending on the host range of the strain. It was concluded that biofilm formation in vitro and in planta for strains of Xcc and Xac was related to their host range, as these processes affect colonization at the early stages of the infection process Citrus canker causes losses in fruit yield and quality. There are no highly effective citrus canker disease control measures. Repeated spray applications of copper are often employed to protect fruit from bacterial infection with consequences for copper phytotoxicity and accumulation in the soil. Alternatively, innate plant defense mechanisms can be enhanced by plant treatments with specific natural and synthetic inducers for control of bacterial diseases. In this study, hexanoic acid applied as a soil drench or foliar spray on 9-month-old potted citrus trees reduced lesions on leaves by 50% compared with control plants. Disease-reducing activity lasted up to 50 days after application. Induction of resistance mediated by hexanoic acid was demonstrated by enhanced expression of Pathogenesis-related (PR) genes and callose deposition in treated and infected plants. These findings indicated that hexanoic acid applications trigger a defensive response in the plants. The application of this natural compound may have potential for management of citrus canker in conjunction with other disease control measures and may reduce the frequency or rate of copper bactericides.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2015
Citation:
Sena-V�lez M, Redondo C, Gell I, Ferragud E, Johnson E G, Graham J H, Cubero J. 2015. Biofilm formation and motility of Xanthomonas strains with different citrus host range. Plant Pathol 64. 767-775.
- Type:
Journal Articles
Status:
Published
Year Published:
2015
Citation:
Redondo C, Sena-V�lez M, Gell I, Ferragud E, Sabuquillo P, Graham J H, Cubero J. 2015. Influence of selected bactericides on biofilm formation and viability of Xanthomonas citri subsp. citri. Crop Protection 78: 204213.
- Type:
Journal Articles
Status:
Published
Year Published:
2015
Citation:
Llorens E, Vicedo B, Lopez MM, Lapena L, Graham JH, Garc�a-Agust�n P. 2015 Induced resistance in sweet orange against Xanthomonas citri subsp. citri by hexanoic acid
Crop Protection 74: 7784.
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Progress 10/01/13 to 09/30/14
Outputs
Target Audience: Citrus canker researchers worldwide and Florida citrus growers managing citrus canker Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? Training for one Ph.D. student in UF-Dept. Plant Pathology How have the results been disseminated to communities of interest? Florida ctitrus grower articles in Citrus Industry Magazine: Graham J, Gruber B, Bock, C. 2014. Research progress for integrated canker management. Citrus Ind. 95(4): 20-24. Cooperative Extension meetings with growers: Florida Citrus Show, “Citrus canker control”, Ft. Pierce, January 29&30, 2014 (300 growers) Citrus Production School, "2014 citrus canker management program”, Desoto Co. Extension Center, Arcadia, Feb. 18, 2014 (40 growers) St. Lucie Co. Extension and Helena sponsored seminar on “Integrated management of canker with reduced copper metallic rates”, Ft. Pierce, March 26, 2014 (70 growers). What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Xanthomonas citri subsp. citri (Xcc), the causal agent of citrus canker, is disseminated by windblown rain associated with subtropical and tropical weather. Water droplets containing bacterial cells are forced through stomata into the substomatal chamber via water congestion at wind speeds in excess of 8m/sec. Bactericidal copper films no longer protect stomatal entry points when the droplets reach this wind speed. Hence, windbreaks are essential for reducing wind speed to improve the efficacy of copper bactericides for reduction of the incidence and severity of canker on fruit of the most susceptible citrus variety in Florida, grapefruit (Citrus paradisi). In an orchard with a perimeter windbreak of Corymbia torelliana, there is a linear relationship between canker incidence (% infected fruit) and wind speed (number of gusts recorded > 4.9 m/sec). An on-going goal is to reduce the rates of metallic copper for protecting fruit. Mixing fixed and soluble copper formulations or a program with fixed copper applied early in the season followed by soluble copper achieves comparable control at 50% of the metallic copper per season. Firewall (streptomycin) is effective for canker control on grapefruit and reduces the risk of copper phytotoxicity to fruit, and may be useful for reducing risk of copper resistance in Xcc. To minimize development of streptomycin resistance, Firewall is limited to two applications per season in late May-early June after applications of copper for control of fungal diseases on fruit, melanose and scab. Firewall reduces risk of fruit infection during tropical weather conditions because streptomycin is locally systemic. Soil drenches or trunk applications of neo-nicotinoid insecticides and Bion (acibenzolar-S-methyl) provide for systemic acquired resistance (SAR) control of canker. SAR reduction of canker on leaves lowers risk of fruit infection. Trunk or soil application of Bion and neonicotinoids at 60 day interval provides comparable control on grapefruit to 21-day interval copper sprays. Integration of non-insecticidal Bion and/or neonicotinoid insecticides may be used to augment copper sprays for disease management.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Bock CH, Graham JH, Gottwald TR. Cook AZ, Parker PE. 2014. Effect of the duration of inoculum exposure on development of citrus canker symptoms on seedlings of Swingle citrumelo. Eur. J. Plant Pathol. 138:237245.
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Bock CH, Gottwald TR, Graham JH. 2014. A comparison of pathogen isolation in culture and injection-infiltration bioassay of citrus leaves for detecting Xanthomonas citri subsp. citri. J. Phytopathology162: 291-301.
- Type:
Journal Articles
Status:
Awaiting Publication
Year Published:
2015
Citation:
Sena-Velez M, Redondo C, Gell I, Ferraguda E, Johnson E, Graham JH, Cubero J. 2014. Biofilm formation and motility of Xanthomonas strains with different citrus host range. Plant Pathology, Doi: 10.1111/ppa.12311.
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Gottwald TR, Graham JH. 2014. Citrus diseases with global ramifications including citrus canker and huanglongbing. CAB Reviews 9: 1-11.
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Progress 02/01/13 to 09/30/13
Outputs
Target Audience: Citrus canker researchers worldwide and Florida citrus growers managing citrus canker Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest? Florida ctitrus grower articles in Citrus Industry Magazine: 1)Graham, J., Gruber, B. Bock, C. 2013. Integrated management of citrus canker. Citrus Ind. 94(4): 12, 14-17. 2) Graham, J. and M. Dewdney. 2012. Research Progress for Management of Citrus Canker in 2012. Citrus Ind. 93(3):15-17. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
1) Reduction/suppression of fruit infection in citrus trees using foliar applications of soluble copper novel bactericidal formulations in comparison with film-forming copper formulations. Standard copper formulations, Kocide 2000, Kocide 3000, Nordox and Champ were less effective than in previous seasons for canker control on Ruby red grapefruit in a season with above average spring and summer rainfall. For example, 2013 fruit canker incidence was ≤ 35% in the copper treatments and ~80% incidence in the UTC compared with 2012 at ≤ 20% incidence in the copper treatments and ~40% in the UTC. Nordox for 5 sprays followed by Magna-Bon at the 100 ppm rate was not significantly less effective than the 1.33 lb of Nordox alone at 50% of the metallic copper per season. Treatments of Nordox 30/30 or Nordox at 0.44 lb combined with Magna-Bon at the 100 ppm rate both at ~50% of the metallic copper per season were significantly less effective than the 1.33 lb rate alone. Magna-Bon at 100 ppm and formulations of Copper Silica Nanoparticle (CuSiNG pH 4, MV1-CuSiNG pH 4, MV2-CuSiNG pH 4) were less effective treatments except than the CuSiNG pH 4 formulated with fixed quaternary ammonium (fixed Quat). The lowest canker fruit incidence achieved with MV1-CuSiNG pH 7 plus Quat was similar to that of the best fixed copper treatments at ~20% of the metallic copper of the fixed copper formulations. For ‘Hamlin’ orange fruit, despite average rainfall, canker incidence on fruit was 44% lower than in the 2012 season due to the overriding effect of HLB on tree vigor and susceptibility of foliage and fruit to infection. As a result, no significant differences among copper formulations were detected in incidence of fruit canker or percentage fruit drop due to canker. 2) Reduction/suppression of inoculum and fruit infection in grapefruit using soil and trunk applications of insecticidal and non-insecticidal SAR inducers.Soil drenches of Actigard and season long rotations with Admire and Platinum were effective for suppressing canker and protecting fruit on young Ruby Red grapefruit trees. The control responses were comparable to those obtained with 21-day copper sprays. Best treatment was a rotation of Platinum 75G, Admire Pro and Actigard combined with season long sprays. These findings are congruent with the recommendation to use neonicotinoid insecticides in rotation for psyllid control (Rogers, 2012) and to integrate their use with protectant sprays of copper. Alternatively, SAR inducers may be applied to the trunk as sprays if there is concern with repeated soil applications leading to risk of leaching or biodegradation in soil. Use of non-insecticidal Actigard also addresses potential concerns for neonicotinoids of non-target effects on beneficial insects. Although not as effective as copper, SAR inducers have substantial disease control activity against scab but little or no activity against melanose. They may be useful to maintain control of fruit fungal diseases should copper applications lapse before the end of period of fruit growth as fruit are still susceptible to late season infection. 3) Xanthomonas citri subsp. citri (Xcc) A strain types are causal agents of Citrus Bacterial Canker (CBC) on most Citrus sp. and close relatives. Two narrow host range strains of CBC, Aw and A*, from Florida and Southwest Asia, respectively, are only able to infect Mexican Lime. Xcc as apoplast colonizing bacteria have to overcome environmental stresses onto the leaf surface and in the apoplastic site besides the plant defenses. Biofilm are survival structures which protects plant related bacteria from deleterious environments and antimicrobials. Several studies have linked the biofilm formation ability of Xcc to the bacterial survival in the plant and to the infection process. However none of them have evaluated if biofilm formation is connected to the distinct behavior of the different strains of Xcc. Differential biofilm formation was observed in vitro and in planta among the Xanthomonas strains assayed. Minimal medium XVM2 contributed positively to biofilm formation for every strain analyzed but wide host range strains of Xcc, which did not show a significant difference between a rich or poor nutrient environment. Narrow host range CBC strains increased drastically the biofilm formation in the minimal media, mostly in strains from Iran. Moreover, in planta, less biofilm formation was showed by the xanthomonads assayed onto non host leaves or fruits. Scanning Electron Microscopy of biofilms onto leaf and fruit surfaces showed differential aggregative structure among the strains with different host range. Finally, on swimming motility large differences among wide and narrow host range strains of CBC were shown. All the strains assayed were able to produce biofilm. However aggregation and biofilm formation in Xcc and Xac is related to the host range of the strains assayed, conceivably affecting the infection process and survival at the early stages of the colonization. Furthermore narrow host range strains of CBC partially countervail the lack of biofilm formation in some media or plants with the higher aggregation in the appropriate niche and an increased swimming motility.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Behlau, F., Hong, J.C., Jones, J.B., Graham, J.H. 2013. Evidence for acquisition of copper resistance genes from different sources in citrus-associated xanthomonads. Phytopathology 103: 409-418.
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Bock, C.H., Graham, J.H., Cook, A.Z., Parker, P.E., Gottwald, T.R. 2013. Predisposition of citrus foliage to infection with Xanthomonas citri subsp. citri. Journal of Plant Pathology 95:99-106.
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Graham, J.H., Myers, M.E. 2013. Integration of soil applied neonicotinoid insecticides and acibenzolar-S-methyl for systemic acquired resistance (SAR) control of citrus canker on young citrus trees. 54:23-243
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Jalan, N., Kumar, D., Andrade, M.O., Yu, F.H., Jones, J.B., Graham, J.H., White, F.F., Setubal, J.C., Wang, N. 2013. Comparative genomic and transcriptome analyses of pathotypes of Xanthomonas citri subsp. citri provide insights into mechanisms of bacterial virulence and host range. BMC Genomics 14: 41500.
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Llorens, E., Lapena, L., Graham, J.H., Garcia-Agustin, P. 2013. A first approach to the use of hexanoic acid as a resistance inducer against Xanthomonas citri. IOBC/WPRS Bulletin 89: 205-209.
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