Biology

Elm grafiosis threatens the Madrid Botanical Garden

The Dutch elm disease, or elm graphiosis , threatens to dry up several hundred-year-old elm trees in the Royal Botanical Garden of Madrid.

What is elm graphiosis?

It is a fungal disease , produced by the fungus Ophiostoma novo-ulmi , which affects several species of the elm family. This fungus is native to Asia, where there are three species of elms ( Ulmus pumila , Ulmus parvifolia and Ulmus wilsoniana ) that are resistant to graphiosis. This would indicate that the fungus has lived with these species for millennia without causing significant damage, such as simple parasitism.

However, this changed dramatically at the beginning of the 20th century. In the Netherlands, a disease that killed elms began to manifest itself. In subsequent years it spread to France, Belgium, the UK and even the USA (in 1931, from logs from France). The disease is commonly called “Dutch elm disease” because it was first detected there, despite being native to Asia.

The Dutch botanist Marie Beatrice Schwarz identified the fungus Ophiostoma ulmi as the cause of elm graphiosis and that the transmission vectors were scolithid beetles of the genus Scolytus . The adult beetles transmit the spores of the fungus between trees and their larvae pierce the trunks (on which they feed), which allows the fungus to access the sap-conducting vessels.

By the 1940s, graphiosis had killed 10-40% of all elms in Europe , which is quite a high number. The plague, however, seemed contained. This changed in the 1960s, when two more virulent strains appeared: one in Europe and one in North America. The fungus causing this new pest was called Ophiostoma novoulmi . The disease spread throughout the US, Europe and Asia, reaching New Zealand in 1989.

The effects of this second outbreak were even more catastrophic. In the United States, it was estimated that the elm population in 1930 amounted to 77 million copies, while in 1990 the figure was reduced by 75%.

Millions of dollars are spent annually throughout the country combating elm graphiosis, between preventive measures for its transmission and felling of affected trees. These two methods, along with planting disease resistant elm varieties, is the existing way to combat the pest.

Damage caused by grafiosis in the Botanical Garden of Madrid

The Royal Botanical Garden of Madrid, founded by order of Fernando VI in Madrid in 1755, is one of the most important botanical gardens in Europe. At present it occupies an area of ​​eight hectares and has live specimens of more than 5,000 species. The garden comprises three tiered terraces with European, American and Pacific plants.

Elm grafiosis threatens
Elm grafiosis threatens

In recent years, two hundred-year-old elms (of the Ulmus minor species ) have been felled because they were affected by graphiosis and threatened to fall. The largest of them had been planted in 1893 and had a diameter of 123 centimeters, while the smallest dated from 1944 and its diameter was 98 centimeters.

The disease also affects the oldest and most emblematic elm tree in the botanical garden, which receives the affectionate name of Pants because its shape (two trunks emerging from the same base) is reminiscent of this garment. His age is estimated at 225 years . The tree has been fighting the disease for years, which has already completely dried up one of its two trunks.

A fungicidal treatment is being applied to reduce the effects of the fungus on the tree, but it is considered that it is impossible to completely eradicate the parasitic organism once it has entered the plant, so that graphiosis is a chronic disease. In case the worst happens and Pants does not survive the disease, four clones of the tree have already been obtained, which could replace it.

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