Failure of what crop caused a food crisis in mid-19th-century Europe?

The European potato failure was a food crisis caused by potato blight that struck Northern and Western Europe in the mid-1840s. The time is also known as the Hungry Forties. While the crisis produced excess mortality and suffering across the affected areas, particularly affected were the Scottish Highlands, with Highland Potato Famine and, even more harshly, Ireland, which experienced the Great Famine. Many people starved due to a lack of access to other staple food sources. The effect of the crisis on Ireland is incomparable to all other places, causing one million deaths, up to two million refugees, and spurring a century-long population decline. The global consequence of this was the creation of a substantial Irish diaspora.

Source: Wikipedia