Powdery mildew, a fungal spore that attacks grapevines, can devastate wine yields. It is a plant pathogen that reduces growth rates, affects grape skin color, and degrades wine quality. The spread of powdery mildew was partly man-made, as European horticulturists imported wild vines from the US, which carried powdery mildew and an infestation of aphids that European vines had no resistance to. This led to the near collapse of the wine industry in Europe in the mid-19th century. European vines were eventually grafted onto American stock to build resistance to these pests. Other powdery mildew species still cause problems with crop growth today.
Powdery mildew is variously referred to as a fungal spore, which is the offspring body of a fungus, or as an actual fungus of the order Ascomycota. It is more commonly known as powdery mildew due to its parasitic nature of existing as a soft film on the surface of host plants such as grapevines. Odium mold can have a devastating effect on wine yields and is known to have contributed to the near collapse of the wine industry in Europe in the mid-19th century.
Within the order Ascomycota for fungi, there is a great variety of forms, but they share the common characteristic of being spore-shooters that distribute their offspring by rapidly dispersing them into the surrounding air. The Oidium group is a subdivision within this order known as a genus that contains dozens of species. Almost all powdery mildew species are known to be plant pathogens that exist and act as powdery mildew agents on the surface of the green parts of vines. They attack the vines and turn them black, as well as turn the foliage yellow in the process, causing the plants to wilt. While a powdery mildew fungus will not always kill the host plant, it will reduce its growth rate and, in the case of vines, affect the grape skin color, which ultimately degrades the final wine product produced from them.
Fungi have a propensity to spread rapidly in moist, cool environments once established, such as vineyards, but the cause of the devastation of wine crops underway in Europe in the 19th century was partly man-made. A worldwide scientific interest in botanical specimens has led European horticulturists to import samples of wild vines from the United States for study. At the same time, Henri Marès, a Frenchman, had developed a method of sulfurizing vines to protect them from powdery mildew infections. The Virginia creepers carried powdery mildew, as well as an infestation of tiny yellow-green aphids of the genus Phylloxera, to which they were naturally resistant. European vines had no resistance to the aphids and they spread rapidly throughout European vineyards over the next 19 years, causing further crop losses from plants that had not already succumbed to powdery mildew.
From 1854 to 1880, the vine became extinct in a large region of Western Europe centered on France, mainly due to attacks by Oidium and Phylloxera, as well as downy mildew and black rot, also present on imported species. It wasn’t until European vines were grafted onto American stock to build resistance to these pests in the late 19th century that crops began to recover. Other powdery mildew species still have problems with crop growth as of 2011. These include the species Oidium lycopersicum which attacks tomato vines and is found throughout the US state of Connecticut and the species Oidium mangiferae which attacks mango trees in the Far Eastern countries of China, India and Pakistan, as well as other regions of the globe such as Mexico.
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