Team:Bio Without Borders/Human Practices


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Human Practices

Initial Research - Citrus Industry And The Disease Impact

Citrus farming is a major industry in Florida. In fact, Florida has 74 million citrus trees spread over 569,000 acres of official citrus groves. Over 76,000 workers work in the citrus industry. The citrus industry brings in more than 9 billion dollars in total revenue. Some estimates have suggested that more than 80% of all citrus trees in Florida are infected by HLB. Over 90,000 acres of Florida's citrus grooves have already been destroyed by HLB in 2017. This citrus disease has spread to almost every other citrus growing region in the United States. That includes the second largest grower of citrus in the US, which is the 2 billion dollar citrus industry in California. Even though the disease has not spread to the commercial farming areas there, the disease could easily cause major damage like in Florida. California in 2019 has 1,400 citrus trees already infected in residential areas, and 1,003 square miles are under quarantine. The citrus industry has been devastated by this disease, losing up to 16% of their revenue over a 5 year period. Many farmers who own citrus trees that are infected by CLas won't get rid of them because it's too costly for them. They use pesticides, put nets over trees, and try to contain the disease while the productivity of the trees slowly diminishes, hoping for a cure to be discovered. These facts are what inspired us to focus our project on reducing HLB, an ongoing problem in our world.

The restrictions caused by the devastation due to HLB in the citrus industry affected the way we approached our project. Because of the dangers that the CLas and Diaphorina Citri pose, we could not just import them from other states and use them in the lab. We decided that we would collaborate with an academic lab already working with citrus psyllids to test our siRNAs. Although we never got that far, Dr. Michelle Heck, a molecular biologist at the Emerging Pests and Pathogens Research Unit at the USDA Agricultural Research Service in Ithaca, NY agreed to test the efficacy of our siRNAs on psyllids in her lab.

Building on the Work of the TecCEM 2017 iGEM Team

When we looked to see if any other iGEM teams had taken on HLB, we found that the TecCEM 2017 team had made a cassette suitable for making siRNAs to interfere with psyllid growth. This team's strategy was to use E. coli deficient in RNAse to host the siRNA-generating part (BBa_K2246000), and extract the siRNA from a culture. They then made nanoparticles of the siRNA and sprayed it on plants. But it ended up killing the plants by blocking their leaves from respiring. So we made some improvements to the project strategy. We decided to see if, similar to nematodes and some other insects, the psyllid consumed the bacteria with the siRNA-generating part, it might be sufficient to silence the target genes.

Expert Interview with Dr. Vidalakis

When we began the project, we talked with our secondary PI, Dr. Vidalakis. He told us that in California the disease has been found in residential area trees, but not yet in commercial groves. Most residential tree owners are not aware of the dangers their trees pose to the industry, and do not get them tested for HLB. Furthermore, even if a tree shows signs of infection, they might not want to cut down infected trees. There have even been cases of infected trees being dug up and moved from one part of the state to another because the owner liked the tree so much! Although there are ethical questions around forcing people to destroy infected trees (their property), it is critical to the survival of the citrus industry. We realized that it would be better to convince folks to voluntarily test their trees, and have them destroyed if they are a danger to others. We decided that part of our human practices would be to spread the word through engaging high school students with a lesson around HLB, and by making it easier for the home citrus owner to test their trees by making a psyllid trap.

Interviews with Citrus Farmer Kris Sutton

To better understand how this disease has affected citrus farmers and how our project might potentially benefit them, we conducted a phone interview with Kris Sutton, a citrus grower in Florida, to better understand their needs.

Interview with Citrus Farmer Kris Sutton

October 9th Call Audio, Questions, & Notes


Human Practices: Outreach

Questions for Kris Sutton, South Florida, Citrus Grower At Faryna Grove Care

  • Faryna grove 1h northeast of Orlando
  • 16 years run as a family business
  • HLB first noticed in South Florida during 2006
  • Greening symptoms full blown around 2010

10-09-2019, 5PM-6PM

Background & Impact

  1. What was your experience like as a citrus grower before Huanglongbing affected your citrus farm?
  • Profitable family-owned citrus farms
  • 2006: HLB discovered in south Florida grove management
  • Business was great until citrus greening disease arrived
  1. How are you able to identify diseased trees in your farm before the problem escalates?
  • Had mottled, yellow looking leaves
  • Initially confused with zinc or manganese deficiency
  • In 2010 Not many trees initially manifested symptoms
  • 151 or so trees per acre, 1 or 2 trees per acre had symptoms
  • In 6 months, symptoms in trees accelerated
  • Waxing in the leaves, dark green to yellow green (50% yellow)
  1. What percentage of your trees have been affected so far? Could you give us an estimate of your loss in profit from the spread of Huanglongbing on your citrus farm?
  • All groves have been somewhat affected -> trees are fighting the disease itself (60-75% of groves; but only visible to around 15% of trees)
  • Not a single grove in Florida without HLB
  • 60-75% are suffering from HLB (only around 15-20% actually visibly show symptoms)
  • Average went from 500 - 750 boxes per acre to 200 - 250 boxes per acre; lost around ⅔ of the profit
  1. Has the rate of affected trees increased over the past couple of years?
  • Can’t tell visually (believe that the situation is getting better)
  • Last 3 years : production went up 10-30%
  • In the last few years hasn’t gotten much worse but has not significantly improved (his personnel grove)
  • Statewide production went up (only last year) before that it went down
  • Personally, the situation is getting better, but in general, the state of Florida's citrus industry is still suffering
  1. Are there any specific anecdotes you would like to share about your citrus trees that we may present to the public to garner more attention on this citrus epidemic?
  • If no effort is made to stop the spread of disease, grove becomes irredeemable
  • 3 years ago an antibiotic called oxytetracycline from NewFarm was presented to help (used recommended 3 sprays); product showed no positive effect to many and nobody continued using it
  • Started injecting microbial product produced by LOCUS into the irrigation system LOCUS-makes the product-
  • Product consists of 1-2 billion live organisms per fluid ounce
  • Only “treatment” the entire state agrees on
  • Recent treatments have restored a number of groves, leading to a small increase in production
  • However, the overall state of Florida is going down in production
  1. In your opinion, how severe would the consequences be if a cure for this disease is not found?
  • Situations will keep getting worse and worse if a solution isn’t found
  • Land prices are growing higher and citrus farming is not as viable/proftable as it used to be
  • People are discouraged from continuing and some are selling the land
  • Within 5 years, there will be severe consequences to the industry

Initial Solutions

  1. What have you done to the trees that have been affected by HLB?
  • When the disease first broke out, trees were removed in droves
  • Takes 3-4 years before a brand new tree can start producing citrus
  • Was costing farmers too much money
  • People are now trying to avoid removing trees and trying to find workarounds with trees that are already infected
  1. What are your primary concerns with adopting bioengineered solutions to your citrus plants? Are there any specific repercussions of past technologies (pesticides and antibiotics) that you’ve had an issue with?
  • In the beginning, there was considerable panic and buying from untrusted salesmen
  • Used to use RoundUp and basic nutritional fertilizers
  • Stayed away from restricted pesticides
  • Doing less, but the situation is getting better
  • Take care to be conscious of wildlife and pollinating insects
  • New products constantly coming out, the person in question has continued to use the products they’ve always used

Suggestions For Us

  1. Would you be open to trying a new treatment for your trees?
  • In the last 2 years, independent companies have come in and requested to use 50 or so trees to test out their products
  • Any loss of profit from those trees is acceptable if solutions are created to help fight the disease
  • If there is evidence of persistent harm to trees, then methods are not allowed. Needs to know what is going on before allowing it.
  • Would like to know exactly what people are doing with the trees before they do it
  • Primary concern is for disruption of the microbiome in their groves.
  1. Is there any advice or things you would like us to look out for in designing our trap for the psyllids transmitting the disease? What would make you more receptive to using our solution to combat the disease? 
  • Experimental treatments might affect microbes in soil, methodology of treatment needs to be transparent
  • Chemical/fertilizer companies have been devoting resources to labeling materials  
  • Already psyllid traps out there - specific colors that psyllids are attracted to, materials such as sticky paper to entrap them
  • Growing more and more popular in groves
  • LOCUS (previously mentioned) is developing a psyllid repellant (like OFF and other bug sprays, details are unknown due to ongoing tests)

Followup Questions

  1. How many trees do you have on your property?
  • Previously stated ~150 per acre, 150 acres to start and 700 acres acquired at a later point
  1. What determines whether or not a product is “approvable” or not
  • Products like microbial products (fertilizer that he’s using currently, herbicide, insecticide, other general use products) - general product, can be used for anything, although it works better on some products than others
  • Other products are supposed to be used only for a specific type of plant - for example, he would only be able to use products labeled for citrus use
  • Some people are panicking to the point they’re hurting the plants - some growers have trees practically covered in chemicals
  • FDA, USDA regulate and label the products


Our initial call with Kris Sutton provided us with the context of how grave the impact of Citrus Greening/HLB has had upon the livelihood growers and the entire citrus industry in Florida as a whole. Cultivating citrus crops, once a viable way to make quite a lucrative, living is under threat to all growers regardless of the size of their operation. The only way for producers of citrus to survive this outbreak is through proactive measures. Managing groves by quarantining affected areas and physically removing infected trees from the property. However since the pathogen is the result of the bacterium Candidatus Liberibacter asiaticus infecting the phloem of citrus plants being transmitted by the Asian Citrus Psyllid (Diaphorina citri) as it feeds on citrus tree; this method of quarantine and removal is only effective up to a certain point.


Second Call: October 16th Call Audio & Notes


Our follow up call with Kris provided our team with the understanding that citrus growers want solutions to Citrus Greening/HLB that are cost effective, directly reduce psyllid populations, and won't lead to unanticipated environmental consequences as a result of their use. Methods to manage psyllid infestations involved the persistent use of pesticides on trees, however may lead to potential unintentional targeting of beneficial insects in groves that are normally pollinators. Methods of directly targeting the bacterium involved applying broad range antibiotics throughout the citrus groves, while this may slow/stop the spread of Candidatus Liberibacter asiaticus it may also kill the ambient microbial populations that are associated with citrus plants and potentially develop antibiotic resistance in soil bacteria through the resulting runoff. Both pesticides and antibiotic use also have a negative consumer opinion, that might make citrus products treated by these methods undesirable to consumers.


The implementation of a trap that lures psyllids into a vessel that contains our RNase-minus HT115 (DE3) E. coli with our siRNA system, would effectively interfere with the expression of genes critical for psyllid development. This would reduce populations of psyllid that are infesting citrus groves, with out the undesirable side effects of pesticides or antibiotic applications to control this disease.



References