With an ever increasing population and global interaction, trade between nations and people moving to and fro poses distinct risks to biosecurity concerns. Human diseases are obviously top of the list, but because they involve direct contamination by humans themselves with other humans, most medical organizations around the world have numerous measures in place to reduce the risk of spreading human pathogens.

But when it comes to pathogens of plants and other organisms that come from the soil, there is much less of a focus. Even though the possibility of the spread of famine from a soil-borne contaminant killing crops around the world is a true scenario of concern. The risk of biosecurity failure from things like tracked dirt in shoes, on shipping containers, and other sources is fairly high, all things considered.

How high though is the question? If a shipping freighter takes 12 months to travel to its target destination, would organisms within encrusted soil even survive? Especially those exposed to the ocean elements? It seems unlikely, but we also just don’t know the answer in full.

The Experimental Setup

Researchers at the company AgResearch, a Crown Research Institute in New Zealand, and the Better Border Biosecurity organization worked together to try and find those answers. They collected soil in Canterbury, NZ from a native forest reserve and an orchard, with three samples from each location making a total of six that were treated as different experimental groups. The samples were placed onto stainless steel trays and lightly compacted to replicate the state of ground soil.

Then, each sample set was split up and subjected to 8 separate treatments. Four involved being placed in cupboards in an unheated shed. The four others involved replicating sea container transport by having the outside of the trays sprayed with high pressure water to mimic container cleaning and then set in disparate outdoor concrete pads. To add up the numbers for you, with 6 soil samples undergoing 8 treatments, there were a total of 48 trays and data points to consider.

Lastly, there was a set of untreated controls, six samples from each of the two sites, and referred to as “fresh soil” in the data. After everything was set up, the trays were left in their locations for months, with a soil microassay conducted on the first day and then on the 3, 6, and 12 month time periods. One confounding factor was that the sea container trays lost a fair amount of soil during that length of time, meaning their tested samples at the 6 and 12 month periods had to be less than during other tests just due to the reduced amount of available soil for testing.

Concerning Survivability

The original assays, found in a study back in January, looked for bacteria counts, with the Pseudomonas genus being its own special category and all non-Pseudomonas bacteria being considered separately, fungi amounts, nematode numbers, and whether any viable plants seeds happened to be in the soil samples. Out of all of those, of special concern were the plant pathogenic nematodes, which could indeed be the source of major crop failure if transported to the wrong location. The study recently released looked more in-depth at just this nematode group of results and the 24 and 36 month data from ongoing testing.

What they found is that while populations across the board did seem to go down for all the microorganisms in the trays (except for the sea container trays on the very top with the most exposure, but that may be due to colonization with bacteria and other organisms out of the air), they didn’t disappear completely in most cases, even after 12 months of more or less isolation. Even some of the nematode species could still produce offspring after that length of time.

Data For Policy Change

The data helped the researchers to rank the worst offenders and create charts including type of transportation, amount of environmental exposure, length of transportation, temperature during transport, and other factors to find how each is involved in the survival of soil pathogens. This will allow for biosecurity organizations around the world to tally up the types of transport of most concern for heightened scrutiny and perhaps to even change how transport is conducted in order to minimize the likelihood of surviving pathogens.

With more research and some structural changes to transportation methods, it should hopefully be possible to lessen the risk of plant pathogens being spread by human travel and transport around the world. Since, without such efforts, we are likely to see a greater and greater spread of crop diseases to other countries as global movement continues to increase.

Press Article Link

Study Link

Photo CCs: CSIRO ScienceImage 2818 Group of Nematodes from Wikimedia Commons

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