The Cambridge Dictionary defines the familiar idiom, “a shot in the arm” as “something that has a sudden, strong, positive effect on something.” It apparently came into popular language as early as 1916, long before the connection between a “shot” became the delivery method for immunization with the introduction of the polio vaccine in 1955. Putting aside the political controversies that have recently risen around getting an injection to prevent COVID infection, there are many beneficial human health therapies that are delivered through an injection (antibiotics, pain medications, cortisone…). There are also reasons that plants can benefit from “getting a shot,” but that has been difficult to do.
Plants get sick too, but unlike humans most of their diseases are caused by fungi and cause localized infections. There are some important plant diseases that are caused by bacteria and viruses and often these pathogens are “systemic” meaning that they are able to spread throughout the plant either in the xylem (water carrying “plumbing” of the plant) or the phloem (the system that distributes the sugars that the leaves generate through photosynthesis. In most cases, these plant pathogens get into their hosts with the help of aphids, leaf hoppers, psyllids and other insects that have the ability to penetrate the plant with their pointed mouth parts in order to feed off of it, but who often “vector” a pathogen in the process. That phenomenon is much like the way that we can get malaria or Zika virus in which case the “vector” is a mosquito. Plants also get systemic infections of certain fungi – often through insect damage.
While getting a shot is a relatively simple process for humans, it can be very difficult for a farmer to protect a crop from its systemic pathogens. The first line of defense is to not to ever introduce the pathogens into a given region in the first place, but that battle has already been lost in many cases. The next option is to try to control the population of the “vector” through insecticide sprays or root drenches. But particularly for perennial crops, there are many systemic plant diseases that remain very challenging to control.
For instance, Pierces Disease of grapevines is a constant bacterial threat to vineyards particularly if they are close to a riparian area where the bacterium and its vector reside. The American Chestnut was once the dominant forest species of much of the Eastern US, but it has nearly been wiped out by a fungal pathogen that is spread by bark beetles. There are virus and bacterial diseases of potatoes that are getting more problematic because Climate Change is allowing their insect vectors to overwinter in broader geographies than in the past.
The Disease Threatening To Destroy The Florida Citru Industry
Citrus trees have several very problematic systemic diseases with the worst one being “Citrus Greening” or HLB (an abbreviation for the Chinese name for the disease which is Huanglongbing). The disease was introduced to the Florida around 2005 and has decimated the orange industry in the Sunshine State reducing production levels to their lowest volume since World War II (see the USDA’s forecast). and threatens other citrus crops like the lemons and tangerines grown in California. The value proposition here is not just tied to the value of the crop in a given year – it is tied to the intrinsic property value of these tropical environments that are still within the US. As of 2021, the Florida citrus industry also supported 35,542 jobs and contributed nearly $7 billion to the economy.
The farmers in the effected region have been employing many different control strategies and have even had to go so far as to grow the trees inside of an insect-proof enclosure at the cost of around $30,000/acre. Genetic engineering solutions have been developed but unlike row crops (corn, soy, cotton…) perennials have a long development path and the potential of resistance is more problematic because it could require replanting. Brand protectionism has also been a barrier to any solution considered to be a “GMO.” There are some control strategies that involve injecting the trees with antibiotics, antimicrobial peptides or biocontrol organisms, but the logistics of doing that for the 200-900 trees on an acre make that very challenging.
A company called Invaio has been working on a method to much more rapidly inject trees with the antibiotic oxytetracycline with a high degree of efficacy. It has been approved by the Florida Department of Agriculture. 30% yield increases can be seen after one treatment, it can be used on young and old trees, and it involves greatly reduced worker and environmental exposure. They have gotten the tree-by-tree injection process down to something that one worker can do for 400 trees in a day. Their goal is to get that to 2,500 trees/day. They sell this as a service using certified applicators. Invaio is now able to deliver the antibiotic oxytetracycline and they are also working on deliver of certain anti-microbial peptides. A system like this could theoretically be used to deliver other agents to citrus and other crops such as beneficial bacterial strains, benign versions of the a virus for “cross protection”, or RNAi. It is always desirable to mix and match “modes of action” for injections in order to prevent the development of resistance in the pest population to any one solution.
While Invaio’s product is currently only registered in Florida for curative treatment, it could have future utility in other citrus industries such as those in California where both the pathogen and vector for HLB now occur, but not yet in key growing areas.
According to Invaio’s Founding CEO, Ignacio Martinez, “Invaio’s Trecise™ technology offers a real breakthrough in the fight against citrus greening and is the first of many treatments we’re planning in our Citrus Health portfolio.”
The hope is that the refinement of this injection technology will allow it to become a viable option in the many other crops that have systemic pathogen challenges.
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