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There are few things more nourishing and comforting than a home cooked meal! Citrus trees under intensive stress from the effects of Greening need a High Intensity Nutritional diet to ensure buds and fruit stay on the trees so ultimately they can produce exceptionally high yields. Yes they can… even with HLB! Pure and wholesome “TKO” Phosphite 0-29-26 and Recover RX 3-18-18 are based on a potent recipe of technical grade materials that are not just stirred together, but bonded with high heat. Sprinkle in Companion® Biological Fungicide as an immune system trigger for a guaranteed disease fighting recipe. Multi-vitamins such as Zn, Mn and B are showcased in our extensive, chloride and sodium free, MicroTech line of 100% chelated micronutrients for high- end sprays will surely get the physicians seal of approval, keeping critical micros levels boosted. Roots deserve a “piece of the pie” too; greening can demolish much of the root mass before appearing above ground! Feed them with BioNutrients Solu- ble AG 8-1-9 loaded with organics including humic acid, L-amino acids, kelp and probiotics.

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hen thinking about genetic engineering, to the next-generation. This type of gene expression is called Methylene Urea the first thing that comes to mind is usually non-stable (or transient). Although it comes with this import- Polymeric Process GMOs (genetically modified organisms) In a ant limitation, non-stable gene expression still holds some WGMO, a genome is engineered to include key advantages. First, since there is no change to the plant additional genetic sequences, usually genes with some useful genome, it will not be considered a GMO and can therefore activity that give the plant an advantage. This method is called escape some of the lengthy and expensive regulatory pro- a stable method because genes will be inherited to the next gen- cesses. Second, these methods are usually much faster to carry TM eration. It is usually very slow, especially with tree crops such as out than generating new transgenic . The major advan- citrus, which have a long juvenile stage that ranges from four to tage of a non-stable plant transformation is that it results six years. It makes introducing and evaluating any genetic trait in a much faster change. Given this advantage (fast) and the G.P. Solutions quality and strength is like comparing Rib-eye to a Twinkie, so call today to plan a a two-decade process. However, this is only one possibility. limitation (non-heritable), non-stable expression methods are successful menu. In theory, it is not necessary to add anything to the usually considered short- to medium-term solutions, until a genome as long as we can find other ways to express desired more stable solution can be found. Free and fast same-day Mark White: (239) 214-1072 900 Cowboy Circle, Labelle, FL 33935 genes. In these other ways, genetic sequences will not be Since making transgenic plants is such a slow process delivery William “Buddy” Putnam, IV: (863) 205-1923 Phone: 863-675-1500 incorporated into the plant genome and will not be inherited in citrus, the biggest advantages transient expression Reese Harvin: (863) 781-2997 www.GPSolutionsFL.com Companion, Essential, Nitro, are registered trademarks of Growth Products, Ltd. 6 Citrus Industry May 2018 Figure 1. Expression of the flowering locus by CTV makes plants flower earlier (A). The effect of CTV RNAi on the establishment of psyllid feed- ing on the plants is shown (B and C). There are high levels of psyllid feeding on control plants (B) versus very little feeding on CTV plants (C).

methods offer is that they are efficient CITRUS TRISTEZA advantage is that this expression is and easy ways to screen candidates VIRUS VECTOR happening in the phloem tissue, where and identify new ones. These systems Citrus tristeza virus (CTV) is a the HLB bacterium is present and the can speed up the search for new gene member of the family Closteroviridae. psyllid insect feeds. candidates that can provide solutions The virus was thoroughly studied Working with CTV is relatively to citrus diseases. Here, we will briefly because it can be used to express for- easier and faster to design, build and describe two methods for efficient, eign sequences of interest. The result carry to plants than CRISPR (see page non-stable gene expression in citrus is a set of vectors that can express a 12) and transgenic plants. Another and address their potential applica- differential level of a gene of inter- advantage of the CTV vector is that it is tions. These methods are the citrus est. CTV expression of a therapeutic available for the current generation of tristeza virus vector and a handheld sequence gives a higher level of expres- plants, especially if a new peptide is dis- gene gun. sion than a transgenic plant. A big covered with the ability to heal/recover Fan-Jet® Single Microsprinklers Superior Performance and Quality

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8 Citrus Industry May 2018 HLB-infected plants. CTV can be used vector. Psyllid adults and juvenile add toxins to the psyllid diet. Upon to express multiple genes simultane- instars suck the citrus phloem sap in sucking the phloem sap from the cit- ously, and there is potential to target order to get nutrients. When doing so, rus plant, these toxins will move to the different aspects of the disease triangle. they will also suck whatever is added psyllid and kill it. In summary, CTV Another use of CTV expression into the phloem sap with CTV. In this expression/RNAi vectors are promising vectors is to rapidly convert HLB- way, researchers are targeting the psyl- tools, which will fast-forward citrus resistant juvenile citrus to maturity. lids by CTV-based expression/RNAi research in the fight against HLB. This is made possible by expressing the vectors via two different strategies. The FT3 flowering locus that induces flow- first strategy is dependent on elimi- HANDHELD GENE GUN ering in citrus seedlings (Figure 1, page nating the expression of psyllid genes The second method for gene deliv- 8). Lastly, CTV can be used for either necessary for their life cycle. We have ery into citrus uses a gun. But this is expression or elimination of expres- selected 15 genes for RNAi targeting. not the kind of gun you will be able sion, in a process called RNAi. The second strategy is dependent on to purchase at the next gun show. The In order to fight HLB using the using the CTV expression vector to only thing this gun shoots is DNA. Its CTV virus vectors, a cooperative net- work among researchers was set up to target the three components of the disease triangle, which includes the citrus plant, the HLB bacteria and the insect vector. With the plant, the first strategy being pursued aims to boost the defense response of the plant by using CTV vectors that individually express short sequences from the HLB bacteria in citrus. These sequences should trigger the citrus plant defense mechanism/s against the HLB bacteria before the infection takes place. Upon entering the citrus plant, the bacteria will face an activated plant defense resulting in tolerance/resistance to HLB. In addition, researchers are also trying to decrease expression of citrus genes that are necessary for the bacteria to cause disease by using RNAi. The second target in the disease triangle is the bacteria itself. Directly screening therapeutic peptides against HLB bacteria is not possible because ® it is not cultured yet. We are using Solicam = Balance the plant phloem tissue, where both CTV and HLB bacteria are present, to Tough on grasses and broadleaf weeds, target it directly in the plant. The first strategy is to target the HLB bacteria while safe on young trees through small natural and engineered antimicrobial peptides (AMP) that are directed at killing or reducing the level Solicam® herbicide from NovaSource delivers the perfect balance between of the bacteria in the phloem tissue. e ective perennial grass and broadleaf weed control, along with safety for Researchers are currently screening the young trees in your citrus grove. more than 100 AMPs for activity against HLB. The second strategy is to And with the additional bene t of maintaining residual control late into the target the bacteria through breaking growing season, SOLICAM provides value that lasts and lasts. its cell wall. A third strategy to target HLB is via the cell-to-cell communica- Contact your crop protection advisor, visit us tion signals called “quorum sensing.” Changes in these signals will affect the at novasource.com or call 800-525-2803 for bacterial movement in the plant and more information. transmission by the insect. Always read and follow label instructions. NovaSource® and Solicam® are registered trademarks of Tessenderlo Kerley Inc. The third and final component of Pat. novasource.com. ©2018 Tessenderlo Kerley inc. All rights reserved. the disease triangle is the psyllid insect

Citrus Industry May 2018 9 A C

B Photos courtesy of C.J. Robertson

Figure 2. A diagram shows how the gene gun works (A). The gene gun is very portable and can be easily used in any desired setting, including the grove (B and C).

bullets are made from plastic tubes that contain many tiny gold expression in citrus leaves very quickly, as short as three days. particles (0.6-micrometer diameter) attached to the DNA to be In addition, researchers can easily scale up the expression lev- delivered into the plant. The gas pressure does not come from els by shooting a leaf at different locations or by bombarding gunpowder combustion, but instead uses helium. Release of many different places in the tree. the helium pressure will propel the gold particles at a very high This system’s efficiency can also enable use of CRISPR- speed and deliver them into the target plant cells (Figure 2). Cas9 in the plant and generate mutations in target genes without making GMOs. Like any good gun, the gene gun Working with CTV is allows the ability to aim carefully and target any particular area of choice, in order to control exactly where the genes will relatively easier and faster be expressed in the plant. For example, researchers are currently testing the use to design, build and carry to of the gene gun in order to directly bombard phloem-rich tissues (such as the bark) to deliver therapies into the place plants than CRISPR. where the HLB bacterium is present. The gene gun is highly portable and can be easily used in any setting. This can allow Unlike CTV, researchers are only beginning to explore the delivery of therapies directly into trees in the grove, if the use of this gun with citrus. But they already have found needed (Figure 2). that in each bombardment event DNA can be delivered to There are still many things to explore with the gene gun. thousands of cells in the citrus leaves, and that these genes are One of the main limitations of the system is that it is costly. expressing active proteins. This method works efficiently with Therefore, studies will be needed in order to determine its every citrus variety that has been examined (Citrus macro- economic feasibility to resolve threats such as greening. phylla, Carrizo, Duncan grapefruit and Madam Vinous), and Researchers are currently exploring the possibilities of this therefore seems to be highly suitable for incorporating DNA system to deliver therapies for HLB. within these plants. Using a gun to introduce DNA and transform citrus plants Amit Levy is an assistant professor and Choaa El-Mohtar is a has many advantages. First, its ease of use allows efficient test- research assistant scientist, both at the University of Florida ing of gene candidates before moving forward to generating Institute of Food and Agricultural Sciences Citrus Research and transgenic plants. Researchers can achieve a high level of gene Education Center in Lake Alfred.

10 Citrus Industry May 2018