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Deadly invaders...

The largest living organism on the planet is a mushroom. Not the fruiting body we are all familiar with but the underground mycelium that makes its way through the soil. The honey mushroom (Armillaria ostoyae), found in Oregon in the USA, covers an area of 965 hectares about 1,350 football fields. This is a parasitic fungus and can invade and consume plants and trees in its path.

The fruiting body of this mushroom, the stinkhorn (Phallus impudicus), is found globally mainly in tropical climates. Apart from the impressive fruiting body they emit a foul-smelling odour reminiscent of rotting flesh. These appeared in my polytunnel after watering my strawberries and have done so every year for the past few seasons. They are attractive to some insects, blue bottles and flies, that transfer the spores after landing on the cap. For most of the year they are active underground before fruiting over a few days then dying back.

Without fungi and bacteria, we would be knee deep in vegetable matter and the action of the fungus in mobilising enzymes to break down plant material releases nutrients into the soil for plants to take up. Other fungus coat the roots of plants working in symbiosis to deliver nutrients and water into the root system The plant benefits from this and the fungi in turn gains vital sugars for its growth.

The arrival of ash dieback fungus into the UK is causing the loss of our native ash trees. Hymenoscyphus fraxineus is a chronic fungal disease of ash trees. The fungus previously widespread in Europe causes leaf loss and crown dieback in infected trees – there is no cure. Like Dutch elm disease before it this fugus has the potential to change the structure of our woodlands and the landscape around us.

With the global movement of plant material such invaders are likely to become more common. Efforts to control at borders with biosecurity measures may be the best way to overt further outbreaks. This will be aided by the introduction of plant passports and border controls in the global fight between host and pathogen. Something that we are all too familiar with as we try to manage the impact of Covid 19 on the global human population.


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