The American chestnut can still be saved from the killer fungus attack

American chestnut has practically disappeared from the entire distribution area due to the attack by the parasitic fungus Cryphonectria parasitica

by Lorenzo Ciotti
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The American chestnut can still be saved from the killer fungus attack

American chestnut has practically disappeared from the entire distribution area due to the attack by the parasitic fungus Cryphonectria parasitica, causal agent of the chestnut cortical canker, accidentally introduced into America on imported Asian chestnuts.

The first documented case of attack was that of a specimen growing in the Bronx Zoo in New York in 1904. Since then, more than 3 billion American chestnuts were destroyed in just a few decades and the species came to the brink of extinction.

A real catastrophe taking into account that many animal species fed on the fruits of these plants, and that according to some estimates they represented about 25% of the trees present on the Appalachian Mountains. Currently, the few plants that have survived within the range have the appearance of large shrubs and large trees can be observed only outside the areas of origin, where the fungus has not arrived.

There are several organizations that deal with the protection of this species, and that try to develop resistance to the pathogen through crossbreeding with species such as the Japanese chestnut, or by resorting to biotechnology and genetic engineering, with promising results for the future.

The American chestnut population was reduced to 1–10% of its original size as a result of the chestnut blight and has not recovered. The surviving trees are frozen in time with shoots re-sprouting from survivor rootstock but almost entirely undergoing blight-induced dieback without producing chestnuts.

According to analysis of old forest dust data, the tree was rare or absent in New England prior to 2,500 years before the present, but rapidly established dominance in these forests, becoming a common tree over a range from Maine and southern Ontario to Mississippi, and from the Atlantic coast to the Appalachian Mountains and the Ohio Valley.

Within it's range, American chestnut was the dominant timber of mountain ridges and sandstone soils. Along the Blue Ridge of North Carolina, the American chestnut dominated the area above the range of the Eastern hemlock and below 1,500 meters.

Description and morphology

It closely resembles the European chestnut and other Castanea species. It is distinguished by the markedly toothed leaves, with very acute apex and teeth. Both the leaves, which appear shiny, and the buds and twigs of the year are completely glabrous.

The leaves are wider than in other chestnut trees. The flowers, like those of the congener species, are carried in catkins, and the female ones are found at the base of mixed catkins. Pollination is done by the wind or by pollinating insects.

The fruits are nuts enclosed in groups of 3 inside the thorny domes. They are smaller than those of the European chestnut, but equally sweet, and are produced in large quantities from the plant. In the past it was of considerable economic importance to the United States for the production of chestnuts and wood.