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Mann K.K.,Citrus Research and Education Center | Schumann A.W.,Citrus Research and Education Center | Obreza T.A.,UFL
Precision Agriculture | Year: 2011

The productivity of a citrus grove with variation in tree growth was mapped to delineate zones of productivity based on several indicator properties. These properties were fruit yield, ultrasonically measured tree canopy volume, normalized difference vegetation index (NDVI), elevation and apparent electrical conductivity (EC a). The spatial patterns of soil series, soil color and EC a, and their correspondence with the variation in yield emphasized the importance of variation in the soil in differentiating the productivity of the grove. Citrus fruit yield was positively correlated with canopy volume, NDVI and EC a, and yield was negatively correlated with elevation. Although all the properties were strongly correlated with yield and were able to explain the productivity of the grove, citrus tree canopy volume was most strongly correlated (r= 0.85) with yield, explaining 73% of its variation. Tree canopy volume was used to classify the citrus grove into five productivity zones termed as 'very poor', 'poor', 'medium', 'good' and 'very good' zones. The study showed that productivity of citrus groves can be mapped using various attributes that directly or indirectly affect citrus production. The productivity zones identified could be used successfully to plan soil sampling and characterize soil variation in new fields. © 2010 Springer Science+Business Media, LLC.

News Article | January 7, 2016

Dutt and Jude Grosser from the UF Citrus Research and Education Center are developing genetically engineered limes containing some similar genetic factors that are expressed in grape skin and blood orange pulp. These modified Mexican limes have a protein that induces anthocyanin biosynthesis, the process that creates the "red" in red wine, and causes the limes to develop a range of colors in the pulp from dark purple to fuchsia. "Anthocyanins are beneficial bioflavonoids that have numerous roles in human well-being," Dutt explained. "Numerous pharmacological studies have implicated their intake to the prevention of a number of human health issues, such as obesity and diabetes." Anthocyanins also naturally occur in a variety of oranges called blood oranges, which has a red to maroon colored flesh and, some say, a better taste than Florida's "blond" oranges. But blood oranges need cold temperatures to develop their trademark vibrant color. They grow and color well in the cooler climates of Spain and Italy, but do not exhibit the characteristic blood red color when grown in the subtropical climate of the Florida citrus belt. These new limes were developed using genes isolated from the red grape "Ruby Seedless" and the Blood Orange "Moro." Research on the utilization of these genes was conducted initially to develop a more consumer-friendly, alternative, plant-derived, system. They are the first step toward Florida farmers producing blood oranges and, possibly, a new grapefruit cultivar. In addition to changing the color of the fruit, the introduction of anthocyanins also change the color of leaves stems and flowers, and could lead to the creation of ornamental citrus plants. "Novel fruit, leaf, and flower colors could be produced by regulating anthocyanin biosynthesis," Dutt said. "Flower color ranged from light pink to fuchsia." Dutt and Grosser's study is being published in the January edition of the Journal of the American Society for Horticultural Science.

News Article | November 23, 2015

Jude Grosser, a professor of plant cell genetics at UF's Institute of Food and Agricultural Sciences Citrus Research and Education Center, and Manjul Dutt, a research assistant scientist at the CREC, used a gene isolated from the Arabidopsis plant, a member of the mustard family, to create the new trees. Their experiment resulted in trees that exhibited enhanced resistance to greening, reduced disease severity and even several trees that remained disease-free after 36 months of planting in a field with a high number of diseased trees. The journal PLOS ONE recently published a paper on their study. "Citrus crop improvement using conventional breeding methods is difficult and time consuming due to the long juvenile phase in citrus, which can vary from four to twelve years, "Grosser said. "Improvement of citrus through genetic engineering remains the fastest method for improvement of existing citrus cultivars and has been a key component in the University of Florida's genetic improvement strategy." Citrus greening threatens to destroy Florida's $10.7 billion citrus industry. The diseased bacterium first enters the tree via the tiny Asian citrus psyllid, which sucks on leaf sap and leaves behind the greening bacteria. The bacteria then move through the tree via the phloem - the veins of the tree. The disease starves the tree of nutrients, damages its roots and the tree produces fruits that are green and misshapen, unsuitable for sale as fresh fruit or, for the most part, juice. Most infected trees eventually die and the disease has already affected millions of citrus trees in North America. Citrus greening was first detected in Florida in 2005. Florida has lost approximately 100,000 citrus acres and $3.6 billion in revenues since 2007, according to researchers with UF/IFAS. Grosser and Dutt's research team used sweet orange cultivars Hamlin and Valencia and created plants that defend themselves against pathogens utilizing a process called systemic acquired resistance, or SAR. SAR provides protection against a broad spectrum of microorganisms and is associated with the production of anti-pathogen proteins. Utilizing SAR has already resulted in the production of transgenic canker-resistant trees. Transgenic trees are those into which DNA from an unrelated organism has been artificially introduced. Disease resistance to greening, also known as huanglongbing or HLB, in this study was evaluated in two ways. First, in a greenhouse study conducted with Southern Gardens Citrus in Clewiston, several hundred trees (clones from several independent transgenic plant lines) were exposed continuously for two years to free-flying, greening-positive psyllids. Trees were routinely pruned and fertilized to stimulate new leaf production. These trees were evaluated every six months for two years for the presence of greening. The insects were also randomly evaluated during this study for the presence of the greening bacterium. Approximately 45 percent of the trees expressing the Arabidopsis gene tested negative for greening. In three of the transgenic lines, the greening bacterium was not detected at all. Control trees tested positive for the presence of greening within six months and remained positive for the entire duration of the study. In the second concurrent study, selected transgenic trees and controls were cloned, grown and planted in fields with a 90-percent HLB infection rate. These trees were similarly evaluated every six months for three years for the presence of the greening bacterium. In this study, one transgenic line remained greening-free for the duration of the study, except for the 24-month sampling period when it tested positive. A second line tested positive at the 30-month sampling period while a third line tested positive at 30 months, but was greening-free at 36 months. Neither of these lines declined in health, and both showed continued growth with periodic flushes. "In addition to inducing resistance to greening, this transgenic line could potentially protect our trees from other important citrus fungal and bacterial diseases such as citrus canker and black spot," Dutt said. The next steps include transferring this gene into additional commercial varieties and rootstocks that are commonly grown in Florida. In addition, researchers must 'stack' this gene with another transgene that provides resistance to the greening bacterium by a completely different mechanism. That will prevent the pathogen from overcoming the resistance in the field. It will still be several years before such trees will be available for commercial use. Explore further: Citrus greening bacterium may 'ring the dinner bell' to attract insect

Penaloza-Vazquez A.,Oklahoma State University | Sreedharan A.,Oklahoma State University | Sreedharan A.,Citrus Research and Education Center | Bender C.L.,Oklahoma State University
Environmental Microbiology | Year: 2010

Pseudomonas syringae pv. syringae strain FF5 is a phytopathogen that causes a rapid dieback on ornamental pear trees. In the present study, the transcriptional expression of hrpM/opgH, algD, hrpR and rpoD was evaluated in P. syringae FF5 and FF5.M2 (hrpM/ opgH mutant). The temporal expression of these genes was evaluated during biofilm formation, the hypersensitive reaction (HR) on tobacco plants, and when the bacteria were subjected to different environmental stresses. The results indicate that mutations in hrpM negatively impair several traits including biofilm formation, the ability to cause disease in host plants and the HR in non-host plants, and the expression of hrpR, a regulatory gene modulating the latter two traits. Furthermore, FF5.M2 was decreased in swarming motility and unable to respond to different environmental challenges. Interestingly, FF5.M2 showed an exponential increase in the expression of algD, which is the first gene to be transcribed during the biosynthesis of the alginate, a virulence factor in P. syringae. The expression of both hrpM and algD were required for biofilm formation, and hrpM was expressed earlier than algD during biofilm develop ment. These findings indicate that hrpM expression is required for several traits in P. syringae and plays an important role in how this bacterium responds to environmental challenges. © 2010 Society for Applied Microbiology and Blackwell Publishing Ltd.

Zambrosi F.C.B.,Instituto Agronomico | Mattos Jr. D.,Instituto Agronomico | Boaretto R.M.,Instituto Agronomico | Quaggio J.A.,Instituto Agronomico | And 2 more authors.
Plant and Soil | Year: 2012

Background and aims: Phosphorus (P) is a mobile nutrient in the plant so growth depends on its internal remobilization and a plant's ability to respond to its availability in the growing media. This study was conducted to evaluate the influence of P status and rootstocks on the patterns of P uptake and remobilization in orange trees. Methods: Sweet orange trees on Cleopatra mandarin (CM) or Rangpur lime (RL) rootstocks were grown for nine months in nutrient solution (NS) that was either P-deficient (DNS) or was P-sufficient (SNS). After this period, half of the trees were reciprocally transferred between DNS and SNS (from D to S and S to D), while the others remained in their initial P availability. Results: Trees on RL had more shoot and root growth, accumulated more P and had greater efficiency of P absorption and transport to the shoot (PAE) than those on CM. The major source of P for growth was previously stored P even with an adequate current P supply to the roots. This suggested the dominance of P remobilization over P uptake and the requirement that trees had sufficient stored P to meet P demand of new growth. Trees on CM had greater concentrations of remobilized P in new shoots than trees on RL. Conclusion: Trees grafted on rootstocks less able to take up P (CM) were more dependent on the internal reserves of P for new growth than rootstocks with higher PAE (RL). © 2012 Springer Science+Business Media B.V.

Ebel R.C.,University of Florida | Burns J.K.,Citrus Research and Education Center | Morgan K.T.,University of Florida | Roka F.,University of Florida
HortScience | Year: 2010

This study was conducted to determine the relationship of 5-chloro-3-methyl- 4-nitro-1H-pyrazole (CMNP) concentration and canopy shaker frequency on fruit detachment force, pre-harvest fruit drop, and mechanical harvesting fruit removal of 'Hamlin' and 'Valencia' sweet orange cultivars. CMNP was applied at 0, 200, and 300 mg·L -1 in a carrier volume of 2806 L·ha -1. Four days after CMNP application, fruit were harvested with a canopy shaker that was operated at 3.0, 3.7, and 4.3 Hz at a tractor speed of 1.6 km·h -1. The experiment was repeated 3× for 'Hamlin' (December, early January, and late January) and twice for 'Valencia' (March and April) during the 2008-2009 harvest season. Fruit detachment force was reduced by at least 50% for all CMNPtreated trees compared with the untreated controls at the time of harvest and was lower for 300 mg·L -1 than 200 mg·L -1 on three of the five dates tested. Pre-harvest fruit drop evaluated immediately before mechanical harvesting was higher for all CMNP-treated 'Hamlin' than untreated controls at all harvest dates, whereas 300 mg·L -1 application resulted in higher pre-harvest fruit drop in 'Valencia' when compared with 200 mg·L -1 or the untreated controls on both application dates. CMNP-induced fruit drop was higher in 'Hamlin' than 'Valencia'. CMNP had a greater effect on fruit removal at lower canopy shaker frequencies. The interaction of total fruit weight removed was not significant on any date as a result of variability among trees in the study. These data indicate that the amount of loosening by CMNP was concentration-dependent and facilitated removal, especially with lower canopy shaker frequencies. Development of viable commercial practices should use the percent of the total crop harvested and not the actual weight of fruit removed in determining efficacy of CMNP and harvest efficiency of the mechanical harvesters.

Mishra A.R.,Citrus Research and Education Center | Karimi D.,Citrus Research and Education Center | Ehsani R.,Citrus Research and Education Center | Lee W.S.,University of Florida
Transactions of the ASABE | Year: 2012

Citrus greening, also known as Huanglongbing or HLB, is a major threat to the U.S. citrus industry. Currently, scouting and visual inspection are used for screening infected trees. However, this is a time-consuming and expensive method for HLB disease detection. Moreover, as it is subjective, the current method exhibits high detection error rates. The objective of this study was to investigate the potential of visible and near-infrared (VIS-NIR) spectroscopy for identifying HLB-infected citrus trees. The spectral data from infected and healthy orange trees of the Valencia variety were collected from four different orchards in Florida. Two different spectroradiometers with a spectral range of 350 to 2500 nm were used to collect the canopy reflectance spectral data. Three classification techniques were used to classify the data: k-nearest neighbors (KNN), logistic regression (LR), and support vector machines (SVM). Analysis showed that using only one canopy reflectance observation per tree was inadequate. None of the classification methods was successful in discriminating healthy trees from HLB-infected trees because of the large variability in the canopy reflectance spectral data. When five spectra from the same tree were used for classification, the SVM and weighted KNN methods classified spectra with 3.0% and 6.5% error rates, respectively. The results from this study indicate that canopy VIS-NIR spectral reflectance data can be used to detect HLB-infected citrus trees; however, high classification accuracy (>90%) requires multiple measurements from a single tree. © 2012 American Society of Agricultural and Biological Engineers.

News Article | March 8, 2016

Cross-section of 'Mexican' lime fruits (A) expressing the VvmybA1 anthocyanin biosynthesis regulatory gene, (B) expressing the Ruby anthocyanin biosynthesis regulatory gene and (C) unmodified control. Credit: Photo courtesy of Manjul Dutt. Anthocyanins, pigments that give plants their red, blue, or purple hues, are not typically produced in citrus fruits grown under tropical or subtropical conditions. Now, scientists have genetically engineered a lime that contains anthocyanins, which they say has several potential benefits. Manjul Dutt, Daniel Stanton, and Jude Grosser, from the Citrus Research and Education Center at the University of Florida, say that the discovery will allow the cultivation of new citrus fruits in the major subtropical citrus belt and/or the production of ornamental plants, depending on the cultivar. The process also creates opportunities for novel fruit, leaf, and flower colors to be produced by regulating anthocyanin biosynthesis. In the study in the Journal of the American Society for Horticultural Science, Dutt, Stanton, and Grosser reported on experiments in which they achieved production of anthocyanins in 'Mexican' lime, a citrus cultivar that does not produce anthocyanin naturally. The scientists produced transgenic 'Mexican' lime (Citrus aurantifolia Swingle) plants expressing either a myb-related anthocyanin biosynthesis regulatory gene cloned from the red grape 'Ruby Seedless' or from the 'Moro' blood orange. The experiments resulted in anthocyanin pigmentation in the leaves, stems, flowers, and fruit. The researchers observed an increased pigmentation of the outer layer(s) of stem tissue in 'Mexican' lime overexpressing the VvmybA1 (from red grape), whereas lower anthocyanin levels were observed in plants overexpressing Ruby (from blood orange). Enhanced pigmentation was also observed in the young leaves; however, pigment intensity levels decreased as the leaves matured. Flower color ranged from light pink to fuchsia. The fruit pulp of several of the lime lines were maroon, similar to a blood orange. "Our report outlines the successful production of transgenic 'Mexican' lime plants, resulting in the production of anthocyanins in a citrus cultivar that does not produce anthocyanin naturally," the authors said. "These plants exhibited unique leaf pigmentation, flower coloration, and pulp enhanced by anthocyanin overproduction." The authors said the newly developed limes could be used as novel ornamental plants or, after rigorous testing, released to fresh fruit markets because of their potential health benefits. They added that the study "opens up the possibility" of developing modified sweet orange or grapefruit cultivars that are anthocyanin-rich and adapted to subtropical environments. More information: The complete study and abstract are available on the ASHS J. Amer. Soc. Hort. Sci. electronic journal web site:

A group of researchers from the University of Florida have taken a new approach to the disease by studying a unique application of lasers on citrus leaves. They have found that lasers, when used with the right settings, could greatly improve the success of antibiotic treatments currently being looked into as a way to stop the deadliest plant disease in Florida's history. The full study is available in the January issue of Applications in Plant Sciences. The bacterium starves trees by attacking the vascular tissue responsible for transporting sugars to developing roots and fruits. Bitter, green, inedible fruits result, and once they appear it is only a matter of time before the tree dies. The search for a cure is costing the citrus industry millions in losses. The susceptible vascular tissue, called the phloem, is the innermost layer of bark. While the disease kills trees from the inside out, scientists are trying to fight it from the outside in. "Effective treatment of this disease has largely been limited by the inability to deliver antibacterial substances to the phloem," explains Ed Etxeberria, a plant physiology professor at The University of Florida's Citrus Research and Education Center. "Penetration of externally applied substances into trees is generally prevented by the presence of protective layers on leaves." Lasers piqued Etxeberria's interest around ten years ago, when he began to help develop laser etching as an ecofriendly, paper-free way to label fruit. Knowing what lasers could do, Etxeberria was drawn to their potential to save infected trees by getting antibiotics into direct contact with infected tissue. "At the moment, there are no effective citrus greening treatments in Florida and worldwide. The use of antibiotics is challenged by the inability to effectively introduce such substances into the phloem," explains Etxeberria. "We found that the use of laser light technology significantly enhanced the penetration of foliar-applied substances across the cuticle of citrus leaves, into the phloem and throughout the tree." The laser beam creates microscopic indentations of approximately 250 μm in diameter. Depending on exposure, the indentation can be as little as a single cell layer deep. The researchers tested two-year-old 'Valencia' orange trees grown in large pots in a greenhouse. They applied test solutions immediately after laser treating the leaves, and examined how far the solutions traveled within each plant using specific fluorescent dyes. Applications of oils on leaf tissue after laser exposure prevented damage. "For large-scale field applications, a scaled-up and more flexible model of the instrument containing multiple nozzles for the laser light, antimicrobial spray, and wax application is being developed. The overall system offers the added advantage of lower application frequencies and hence reduction in chemical use, a condition that lessens environmental impact," explains Etxeberria. The laser perforation method can also be applied to other research initiatives, such as in studying the velocity of phloem sap flow and for the delivery of other agrochemicals such as fertilizers, systemic fungicides, and insecticides.

Cesar Bachiega Zambrosi F.,Instituto Agronomico | Mattos D.,Instituto Agronomico | Syvertsen J.P.,Citrus Research and Education Center
Journal of Plant Nutrition and Soil Science | Year: 2011

Some 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. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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