Serratia, Mi Encanto: How Biological Control Agents Can Mitigate Colombia’s P. cinnamomi Crisis

In Disney’s new film Encanto, Colombian singer Carlos Vives describes Colombia as a paradise. “Todos llegan para gozar,” he sings–everyone comes to enjoy Colombia’s bounty. Despites its relative prosperity as an upper middle income country, however, Colombia’s development has been lopsided. Its income distribution is heavily weighted towards the top-earning 10% of the population, who, as of 2019, hold 40.3% of the country’s wealth–leaving 42.5% of the population beneath the poverty line and 15.1% of the population in extreme poverty. Most of this poverty is concentrated in Colombia’s rural districts, whose populations mainly comprise small subsistence farmers. This places Colombia at seventh in the world for income inequality.

In order to understand why rural areas of Colombia are in such severe straits, it is helpful to understand Colombia’s history. Colombia came into being as a country in 1499, when the Spanish encountered Colombia’s Caribbean coast in the region now known as La Guajira. The country underwent a tumultuous succession of regimes after its liberation from the Spanish empire in 1810, finally becoming the Republic of Colombia in 1886. Shortly afterwards, the country was ravaged by the first of its periods of civil warfare. This first period, La Guerra de Los Mil Días, wherein 120,000 people died, was rooted in turmoil between the Partido Conservador Colombiano and the Partido Liberal, Colombia’s conservative and liberal parties. Only fifty years later–in 1948–another period of warfare caused by rifts between the parties took hold of the country, this time in the form of a ten-year war that killed 300,000 people. This period, termed La Violencia, culminated in the formation of the National Front, where both parties agreed to alternate positions of power, a pact that lasted until 1974.

While the Front put an end to the war, it was also the impetus for Colombia’s history with guerrilla warfare and drug trafficking. As socioeconomic and political problems continued to develop in the 1960s, left-wing extremist groups began to form–notably, the Revolutionary Armed Forces of Colombia, commonly known by their Spanish acronym FARC. In the 1970s and 1980s, the FARC and other guerrilla groups–like the M-19 (Movimiento 19 de Abril), the ELN (Ejército de Liberación Nacional), and the EPL (Ejército de Liberación Popular)–became increasingly involved with drug cartels, upon whom they relied on for financial support. By the late 1990s, drug production and unemployment were running high. Guerilla groups regularly assassinated government officials and politicians, leading to the emergence of far-right paramilitary groups–like the AUC–whose primary mission was to combat the guerrilleros by any means possible, including by terrorizing citizens suspected to be allied with them.

Although the violence was widespread, it concentrated itself in rural areas. One such area was Pichilín, a tiny village in los Montes de María, which lie on Colombia’s Caribbean Coast. Los Montes are one of the most vibrant epicenters for biodiversity in Colombia–itself the second-most biodiverse country in the world–but, up until the early 2000s, they were an epicenter for guerrilla warfare, too. One Pichilín resident, who remains nameless, said that a paramilitary group arrived one afternoon with no warning. Her story is one of many, but still singularly devastating: four weeks pregnant, she was easy prey for the guerrilleros, who took her captive in a local house along with a few other women. “We thought it was the end of us,” she said. “They [were] going to kill us.” Even after the AUC was dissolved in 2006 and the FARC signed a ceasefire treaty in 2017, the turmoil continued to damage Colombia’s social fabric. “Pichilín lived in a period of fear, of loneliness,” said the resident. “A car would come into the town and we would run.”

But isolation and paranoia were not the only blights brought by the conflict. In the late 2010s, avocado farmers began to notice a strange phenomenon. The fruits of their avocado trees began rotting at the stems while still growing on the trees; the tree crowns began to thin as leaves wilted and discolored. When leaf fall finally came, the avocados were small, hard, and–most problematically for the farmers–impossible to cell.

The culprit is Phytophthora cinnamomi, “one of the most devastating plant pathogens known” according to a 2018 study. P. cinnamomi is an oomycete, a fungus-like organism that breaks down organic matter. Like many oomycetes, P. cinnamomi can lie dormant within an infected plant, and it is this, as well as its adaptability to different environments, that makes it so dangerous. P. cinnamomi’s chlamydospores—spores that it uses to spread, like seeds—can survive up to six years without nutrients, allowing the pathogen to spread stealthily over an extended period of time. When a chlamydospore is finally exposed to soil containing a certain mix of amino acids and root-originated compounds, it germinates to produce sporangia. These structures make spores called zoospores that specialize in entering and colonizing plants by breaking through non-woody tissue. Once the zoospores have entered a plant, usually through its roots, they begin to rot the tissue. If that wasn’t deadly enough, the pathogen then emits toxins that stop water flow, leading to the death of leaf cells. P. cinnamomi’s devastating effects make it a well-known danger in the United States, Europe, and Australia, but in El Carmen de Bolívar, the largest town in los Montes de María, it is an entirely new kind of killer.

The origins of P. cinnamomi in Los Montes are still nebulous, but its presence only became notable shortly after the conflict, during which Los Montes were alive with activity. Since the movement of people and their associated livestock, vehicles, and gear is correlated with a higher chance of pathogen spread, it is entirely possible that one of the many armed groups passing through Los Montes spread the pathogen to the area. The pathogen’s chlamydospores could have been caught anywhere from the crevices in their boot soles to the dirt in their tires. Further aggravating the spread of the pathogen would have been the lack of agricultural management. Many families were displaced during the conflict, whether because of illegal land seizure, violence, or hunger—meaning that farmers couldn’t see the initial signs of the infection until it was too late to stop the spread.

“Us here in Montes de María,” said the resident, “we are fans of agricultural production. Ultimately, the production is for us to live.” The residents of Pichilín specialize in growing yuca, cassava, maize—in fact, they depend on it; in El Carmen de Bolívar, residents depend on avocados to live. With the arrival of P. cinnamomi, all their livelihoods are threatened. 

But the ramifications of P. cinnamomi’s new presence in rural Colombia go beyond the livelihoods of Los Montes’ small farming communities. P. cinnamomi has, after all, decimated the sweet chestnut forests of Europe, endangered dozens of endemic species in Australia, and put over four thousand more species at risk. If the pathogen were to extend its borders in Los Montes for only a few more miles, it could wreak havoc on Colombia’s forests, too. Los Montes are home to no less than three protected forest areas, one being the Los Colorados sanctuary. Besides being an International Union for Conservation of Nature (otherwise known as IUCN) protected area, Los Colorados is home to over 208 species of birds and forty-four species of mammals, among which is the endangered gray-bellied monkey. All those species, however, depend on the flora of Los Colorados, to which the appearance of P. cinnamomi would be a death sentence.

In previous cases, South American farmers have attempted to stave off P. cinnamomi using integrated disease management methods. However, these methods–which include strategies such as adding potassium silicate to soil and spraying plants with pesticides–are designed for large-scale farming operations. Not only could they be potentially harmful to other ecosystems in the Los Montes area, they are impractical and expensive to implement on a small scale. A holistic approach—one appropriate for small farms—would be more effective for the farmers in Los Montes. However, these kinds of approaches are not nearly as immediate or successful. And that’s a problem.

After decades of conflict, Colombia’s economy has been severely damaged. The recent influx of Venezuelan refugees—a mostly jobless and resource-depleted population—has only aggravated Colombia’s economic plight. And, when the pandemic hit, Colombia implemented strict lockdown procedures—but with a population that mostly deals in in-person employment and cash payments, thousands were put into severe financial straits. Conflict—this time spurred by civilians—is threatening to break out again. All of this means that the Colombian government is eager for an economic boost, one which could easily be provided by more large-scale farming operations, which usually grow cane sugar, coffee, or oil palm monocultures. The small-holder farmers of Los Montes, a region famous for its fertility, are already under pressure to turn their land over to large-scale farming operations, but the Colombian government will sooner seize their land for companies that can afford integrated disease management methods than invest resources in solutions for small-scale farmers.

The consequences of losing Colombia’s subsistence agriculture communities could be severe, however. As large-scale farming operations push small farmers to urban areas, the economic recovery Colombia is undergoing could take a significant blow. In the countryside, farmers have the freedom to set their own rates, giving them a modicum of control over their income; when they move to cities, however, they are outpriced by urban sellers. This means that many displaced families end up unemployed or with irregular employment, exacerbating poverty, malnutrition, and housing issues already prevalent in Colombia’s low-income urban areas.

One method, however, could save the future of Colombia’s small farming communities. Biological control agents, or BCAs, are a developing frontier in agriculture, and are being used to mitigate pests, boost plant growth, and strengthen environmental tolerance. Traditionally, biological control methods have entailed pitting natural enemies against each other: if an area were to become infested by invasive mice, a biological control method would dictate sending in a natural enemy—like hawks or snakes—to cut back the invasive population. This kind of biological control has its critics; species released to mitigate invasive groups often become invasive themselves, precipitating a hellish cycle of initial control and subsequent loss of it. Recently, however, biocontrol has extended to strains of microorganisms and GMOs. It is this kind of BCA that could be the key to stopping P. cinnamomi.

In a 2020 study published in the Journal of Integrative Agriculture, a group of researchers led by David Granada found that a strain of Serratia bacteria be used to combat P. cinnamomi root rot. The strain was selected from “indigenous antagonistic isolates”—antagonistic here meaning anti-oomycetic—found in avocado trees from the region of Antioquia. (It is worth noting that while some indigenous avocado varieties have shown resistance to P. cinnamomi, Colombia’s position as an international monolith of avocado production prevents it from straying too far from the known commercial varieties.) Granada and his team watered infected seedlings with a water/oil emulsion containing Serratia, distilled water, palm oil, and traces of other compounds. What they found could be groundbreaking: the Serratia strain was so effective in combating the infection that, when Granada and his team re-examined the seedlings only ten days later, there were no traces of P. cinnamomi left: not only had the strain halted the infection, it had completely eliminated it.

The ready availability of a Serratia emulsion similar to the one mixed in the study could be a lifesaver to the farmers of los Montes, especially since it would combat the most economically damaging effect of P. cinnamomi infections–plant death. It has its limitations: part of the problem with BCAs is that strains react differently in certain climates or ecosystems; Serratia may not be as effective in los Montes as it is in Antioquia. If the strain fails, if it is inaccessible, or if it is unaffordable, the Colombian government, desperate to regain economic footing after decades of internal conflict, will look away as their land is turned to cash-crop fields. But, as one farmer in los Montes put it, “Agriculture is not assured.” Should the Serratia emulsion succeed, rural farmers–both in Colombia and across the world–will be able to put food on their tables for decades to come.

Serratia, Mi Encanto: How Biological Control Agents Can Mitigate Colombia’s P. cinnamomi Crisis” was awarded an Honorable Mention in the 2022 Scholastic Arts & Writing competition. It was presented at the North Carolina Youth Institute for the 2022 Global Youth World Food prize.

1 Comment

  1. Michele frattad says:

    Very interesting and well written!!!


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