Combating huanglongbing and canker via genetic engineering of citrus

Manjul Dutt, Ahmad Omar, Vladimir Orbovic, Gary Barthe, Julie Gmitter, Monica Vasconcellos, Charles Dunning, Jude W. Grosser

Abstract


Florida is the world’s third largest producer of citrus, behind Brazil and China. In recent years, this 9 billion dollar industry has been affected by two important diseases—citrus greening, also known as huanglongbing (HLB) and citrus canker. Both these diseases are caused by gram negative bacteria. Although canker can be managed by following a canker suppression program, HLB affects all cultivated citrus varieties and cannot currently be controlled, except in the absence of the psyllid insect vector. Resistance to either HLB or canker is also not present in commercial orange and grapefruit cultivars. A strategy to produce resistant citrus is through genetic engineering by incorporating resistance genes not found in citrus. We have successfully cloned several natural and synthetic antibacterial genes and made significant progress in introducing them into commercial sweet orange and grapefruit cultivars using both the standard Agrobacterium-mediated transformation system, and the protoplast/Green Fluorescent Protein (GFP) transformation system developed previously in our program. Genetic constructs containing promoters that target genes exclusively in the phloem tissue, where HLB resides, are also being utilized in efforts to minimize foreign gene expression in fruit or juice subsequently going to market. Techniques for construction and incorporation of the genes into citrus are discussed.

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283