Potato late blight was prevalent in Ireland from 1845 to 1846. Within a few weeks, the local potatoes became rotten, and the potato yield was severely reduced or even eliminated. Several years of epidemics finally led to famine. Hundreds of thousands of people starved to death, 1.5 million people fled their homes and fled to America, and many more crossed the sea to England. This incident shocked the whole of Europe and the world. You must know that the population of Ireland at that time was only more than 8.3 million. According to conservative statistics by some scholars, Ireland's registered population has decreased by at least nearly 3 million. If ranked by the proportion of population death or reduction caused by a certain event, famine in Ireland far exceeded Two world wars.

What is the culprit causing this rare famine in human history? On the surface, it is the connection of the following three causal relationships, that is, continuous rainy weather caused potato late blight - late blight caused a reduction in potato production - potato shortage caused famine. It seems that meteorological factors are the trigger. If so, we can blame God.

Now let's take a look at how potatoes became a food that local people depended on for their survival. As we all know, the traditional crops in European history were various types of wheat. The varieties and planting methods of traditional crops allowed Europeans to obtain small but relatively stable harvests, and the population was also relatively stable. Potatoes were introduced to Europe from the New World in the 16th century. First introduced to Spain in 1553, potatoes were first brought to Britain when the British defeated Spain in the Caribbean in 1586. For a long time, potatoes were used as ornamental flowers and livestock feed. On the eve of the French Revolution, the royal family used potato flowers as ornaments but did not dare to eat them. At that time, Britain was a poor country with food shortages. It happened that the climate in Ireland was also suitable for potato cultivation, so potatoes were widely grown in Ireland. By 1650 potatoes had become Ireland's main food crop. At the same time, Ireland's population increased from 1.1 million in 1672 to 5.2 million in 1801, and to 8.3 million in 1846. This short period of population growth is unprecedented in history. However, monoculture planting of crop species poses huge risks to food security production.

Planting a crop year after year and over a large area will inevitably provide certain parasites with abundant nutrients and the time and space they need to become popular. This is the material basis for the epidemic of late blight. Another deeper question concerns genetics. Tracing back to the potato introduction work in Europe at the end of the 16th century, we found that there were only two clones of potatoes introduced from South America, which were introduced to Ireland and gradually developed into a major crop. Most of the varieties grown locally are descendants of those two clones, and their genetic background is quite narrow. The investigation found that in the Andes Mountains of South America, where potatoes originate, late blight occurs frequently but never as severely as in Ireland. This is because the potato population contains complex and diverse individuals and contains rich genetic genes. It is this diversity of hosts that cultivates the same diversity of pathogens. It is impossible for any of their small species to significantly surpass other small species and grow alone, because the plants they can overcome are only a small part of a huge group. part. It is assumed that there may have been some small species in history that could be infected in large numbers, but the diseases they caused would reduce the number of infected plants, which in turn restricted the development of those small species. However, there is a lack of this natural balancing mechanism in farmland, and deviations in artificial introduction are often a major source of outbreaks of pests and diseases.

(The author is a senior consultant of Sinofert Co., Ltd. and a professor of China Agricultural University)