News Article | May 17, 2017
UF/IFAS researchers have discovered that a mandarin hybrid developed by colleagues contains cellular activity – known as metabolites—that makes it more able to fend off greening than most other types of citrus. That's hopeful news in the state's battle against the disease that's severely damaging Florida's multimillion dollar-a-year industry. It also furthers the evidence that 'LB8-9', also known as Sugar Belle, is a good, greening-tolerant mandarin hybrid. In 2016, Florida citrus nurseries grew more Sugar Belle trees than any other mandarin hybrid except for one, demonstrating grower interest in the variety, said UF/IFAS horticultural sciences professor Fred Gmitter. From field observation, scientists with UF/IFAS found the Sugar Belle mandarin is less affected by citrus greening than other mandarins, said Nabil Killiny, an assistant professor of plant pathology. Researchers want to know what makes the Sugar Belle resistant. Killiny's study focused on identifying the chemicals found in Sugar Belle trees that have been shown to fight against diseases in other plants. Scientists at the UF/IFAS Citrus Research and Education Center in Lake Alfred, Florida found Sugar Belle mandarin is high in several volatiles and beneficial compounds – known as phenolics. These findings could tell scientists why Sugar Belle mandarin is more tolerant to Huanglongbing, or HLB, also known as citrus greening. "The results of this study gives more insights about the mechanism behind tolerance of some citrus cultivars to HLB," Killiny said. "Understanding of the mechanisms behind tolerance to HLB could help in developing economically tolerant citrus cultivars." Researchers tested volatile and non-volatile metabolites of the greenhouse-grown mandarin trees. Among other traits, volatile metabolites emit odors, while non-volatile metabolites do not. To analyze the metabolites, they used gas chromatography - mass spectrometry and found the Sugar Belle mandarins to be relatively tolerant. Other newly released mandarins should be further evaluated using greenhouse-controlled studies, the paper says. If tolerance of these hybrids is confirmed, they could be used to replace the traditionally susceptible cultivars. Gmitter and UF/IFAS professor Jude Grosser, co-authors on the new study, developed and released Sugar Belle mandarin in 2009 and say they're very popular with growers. The mandarin hybrid—a mix of the sweet Clementine and the colorful, bell-shaped Minneola—has a rich taste and strong aroma, Gmitter said. The sweet-tart fruit may be best described as a mandarin with a tangy punch. Since it spread to the Americas, greening has killed millions of trees and caused a sharp decline in production in many citrus growing regions. Field observations of hybrid citrus, such as the Sugar Belle, showed them to be greening tolerant, the study says. The study is published in the journal Plant Physiology and Biochemistry. More information: Nabil Killiny et al. Metabolically speaking: Possible reasons behind the tolerance of 'Sugar Belle' mandarin hybrid to huanglongbing, Plant Physiology and Biochemistry (2017). DOI: 10.1016/j.plaphy.2017.05.001
News Article | May 17, 2017
While citrus greening disease has blemished the Florida industry, University of Florida scientists have developed a mandarin hybrid that seems to be winning the battle. Now, researchers are learning what makes this fruit a fighter. UF/IFAS researchers have discovered that a mandarin hybrid developed by colleagues contains cellular activity -- known as metabolites -- that makes it more able to fend off greening than most other types of citrus. That's hopeful news in the state's battle against the disease that's severely damaging Florida's multimillion dollar-a-year industry. It also furthers the evidence that 'LB8-9', also known as 'Sugar Belle®', is a good, greening-tolerant mandarin hybrid. In 2016, Florida citrus nurseries grew more 'Sugar Belle' trees than any other mandarin hybrid except for one, demonstrating grower interest in the variety, said UF/IFAS horticultural sciences professor Fred Gmitter. From field observation, scientists with UF/IFAS found the 'Sugar Belle' mandarin is less affected by citrus greening than other mandarins, said Nabil Killiny, an assistant professor of plant pathology. Researchers want to know what makes the 'Sugar Belle' resistant. Killiny's study focused on identifying the chemicals found in 'Sugar Belle' trees that have been shown to fight against diseases in other plants. Scientists at the UF/IFAS Citrus Research and Education Center in Lake Alfred, Florida found 'Sugar Belle' mandarin is high in several volatiles and beneficial compounds -- known as phenolics. These findings could tell scientists why 'Sugar Belle' mandarin is more tolerant to Huanglongbing, or HLB, also known as citrus greening. "The results of this study gives more insights about the mechanism behind tolerance of some citrus cultivars to HLB," Killiny said. "Understanding of the mechanisms behind tolerance to HLB could help in developing economically tolerant citrus cultivars." Researchers tested volatile and non-volatile metabolites of the greenhouse-grown mandarin trees. Among other traits, volatile metabolites emit odors, while non-volatile metabolites do not. To analyze the metabolites, they used gas chromatography -- mass spectrometry and found the 'Sugar Belle' mandarins to be relatively tolerant. Other newly released mandarins should be further evaluated using greenhouse-controlled studies, the paper says. If tolerance of these hybrids is confirmed, they could be used to replace the traditionally susceptible cultivars. Gmitter and UF/IFAS professor Jude Grosser, co-authors on the new study, developed and released 'Sugar Belle' mandarin in 2009 and say they're very popular with growers. The mandarin hybrid -- a mix of the sweet Clementine and the colorful, bell-shaped Minneola -- has a rich taste and strong aroma, Gmitter said. The sweet-tart fruit may be best described as a mandarin with a tangy punch. Since it spread to the Americas, greening has killed millions of trees and caused a sharp decline in production in many citrus growing regions. Field observations of hybrid citrus, such as the 'Sugar Belle,' showed them to be greening tolerant, the study says. The study is published in the journal Plant Physiology and Biochemistry.
Mann K.K.,Citrus Research and Education Center |
Schumann A.W.,Citrus Research and Education Center |
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.
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: journal.ashspublications.org/content/141/1/54.abstract
News Article | January 13, 2016
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.