It's Not Always Greener on the Other Side

The term “citrus greening” might sound harmless at first. “Citrus” refers to fruits like oranges, tangerines, and grapefruit. These fruits pack a punch for your vitamin C fix. But when we are ready to eat these fruits, green is not the color you are looking for (an orange should be orange, of course). Citrus greening (also called Huanglongbing or HLB) is a disease of citrus plants that is the opposite of harmless; it results in the depletion of orange harvests.

The disease is caused by a bacteria, Candidatus Liberibacter asiaticus, which is transmitted by a particular insect (Asian citrus psyllid) on the plant leaves. This has become a major issue for orange groves around the globe, but especially in Florida, where 90 percent of citrus groves are affected. The U.S. Department of Agriculture (USDA) has cited that Florida orange production has declined significantly for 2016-2017.

Citrus Grove Guru Guidance

To get more insight on citrus greening, we spoke with Dr. Michael Rogers, Citrus Research and Education Center director and associate professor at the University of Florida’s Institute of Food and Agricultural Sciences (UF-IFAS).

“Since citrus greening disease was first found to be present in Florida in 2005, it has spread throughout the state and is now causing reductions in the citrus crop in all commercial citrus groves in the main commercial citrus growing regions of the state,” said Dr. Rogers. “Since the 2003-2004 harvest season, citrus production has been reduced due to a number of factors including hurricanes, some mild freeze events and loss of groves to urbanization. However, the primary factor driving reduced citrus yields today is citrus greening disease.”

Dr. Rogers explained that not only does this mean that fewer oranges are harvested, but growers must spend more money to keep their groves in production. The economic implications for growers and consumers can be explained more in this University of Florida 2017 publication, “Evolution of Citrus Disease Management Programs and Their Economic Implications: The Case of Florida’s Citrus Industry.”

To combat citrus greening, growers are using timed insecticide spraying to manage psyllid populations. But this only works for a short period of time. Dr. Rogers also noted that another option is to nurture the root system of the tree (to enhance water and nutrient uptake from the soil) since the citrus greening disease harms the trees by impacting water and nutrient absorption.

“While supplemental nutrition or irrigation is not a cure for the disease, there is anecdotal evidence from growers that this additional effort appears to be extending the life of the tree, although the yields are still reduced," said Dr. Rogers.

Biotechnology Beats Down Bad Bacteria

Our orange groves need a hero! It’s biotechnology to the rescue (cape flaps in the wind)! Biotechnology advances are (safely and effectively) helping to save the oranges by negating the effects of the bacterial infection caused by the psyllid, but public perception of these techniques is a barrier to use.

To dig deeper, we asked Dr. Fred Gmitter, professor of horticultural sciences at UF-IFAS, about biotechnology and its impact on thwarting the psyllid’s impacts.

“There are many approaches being taken to provide what could be long term and profound genetic solutions to the citrus greening disease problem,“ said Dr. Gmitter, “…traditional genetic engineering and more recently the possible applications of genome editing strategies, using the CRISPR/Cas 9 system for example.” The CRISPR/Cas 9 system can be used to switch off plant genes that make the plant resistant to the infection.

“What now is considered to be traditional GMO technology has been used to develop potential new varieties with resistance to greening,” said Dr. Gmitter. “It is hoped that these approaches, reliant on genetic elements already pre-existing in the citrus genome, may not only function to yield citrus plants that are tolerant of or resistant to the disease, but that may also find better acceptance in the marketplace among producers and consumers of citrus fruit and products. Such new trees are being tested in greenhouses and in field plots and several are showing promise.”

Orange You Glad We Have Food Science

These scientific advances are heroes in our book. They are fighting off pests that are devastating citrus crops and putting a burden on farmers and our food supply. With more scientific advances in biotechnology to help fight crop disease, there looks to be even more hope for our beloved oranges.