Citrus greening, also known as Huanglongbing, has been a problem for citrus farmers since its discovery in China in 1915. Since then, it has caused the loss of millions of citrus trees and has spread to all Asia, Africa, South America and North America. The disease was first discovered in the United States in 2005 in the Miami, FL area and has since then spread to all countys where citrus grow. [1]
The disease is thought to be caused by the Candidatus Liberibacter bacterium, which enters the phloem of the plant. This makes the disease incredibly hard to treat once a tree is infected because the bacteria is located in the vascular system of the plants. [1] The bacteria is then transmitted between plants by the Asian Citrus psyllid fly.
Citrus greening has caused a 50% decrease in citrus production in Florida, since the arrival of the disease. The disease is threatening the whole citrus production industry in Florida, which is valued at $3.3 billion. [2]
Biotech and agriculture companies have been trying to come up with a treatment or a means to stop the spread of this disease. In February, developers at the agricultural production company Southern Gardens Citrus proposed a new treatment to the USDA that recently entered the consideration phase. Southern Gardens Citrus’s proposal involves genetically engineering the citrus tristeza virus (CTV) to attack the bacteria that causes citrus greening. The genetically engineered CTV comes from a harmless strain of the virus and will express a defense gene discovered in spinach. [2]
Previously, Southern Gardens Citrus has been also attempting to genetically modify the citrus plants themselves to express the spinach defense gene, but they fear being labeled as a GMO. The hope is that by using the CTV to attack the C. Liberibacter through expressing the gene itself, that the plant will not be labeled as a GMO. By expressing the gene itself the CTV will not alter the genome of the plant directly. [2] Currently the CTV treatment is under review by the FDA and undergoing field trials. If passed by the FDA it would be the first of such a treatment approved for commercial use. [2] The hope for the treatment is to stop the spread of this deadly disease that is putting the citrus industry in great jeopardy without having to resort to the public stigma and reproach of being labeled a GMO.
References:
[1]"Citrus Greening (Huanglongbing)." UF/IFAS Citrus Extension: Plant Pathology. Accessed May 17, 2017. http://www.crec.ifas.ufl.edu/extension/greening/index.shtml.
[2] Ledford, Heidi. "Geneticists enlist engineered virus and CRISPR to battle citrus disease." Nature 545, no. 7654 (2017): 277-78. doi:10.1038/545277a.