Do potatoes have “natural enemies”?

Potato (Latin name: Solanum tuberosum, English: Potato), also known as potato, yam egg, ground egg, sweet potato, Dutch potato, etc., is a perennial tuber of the Solanaceae family.

Potatoes are usually planted once or twice a year and have high nutritional value and high yield.

Currently, it is the fourth largest food crop in the world after wheat, rice and corn.

Potatoes originated in the Andes Mountains in South America and later gradually spread to Europe, North America and Asia.

In my country, potatoes were first introduced during the Wanli period of the Ming Dynasty (more than 400 years ago) as a non-indigenous crop. Currently, they are widely planted in Northeast China, Northwest China, South China, and Inner Mongolia.

my country ranks first in the world in both potato production and cultivated area, and is undoubtedly the world's largest potato producing country.

In 2015, my country launched a strategy to make potatoes a staple food, striving to process them into steamed buns, noodles, potato starch, etc., and make them another staple food in my country after rice, wheat and corn.

Like other crops, potatoes are susceptible to diseases.

Among them, late blight caused by infection with Phytophthora infestans is the most notorious.

The direct economic losses caused by this disease around the world each year amount to tens of billions of dollars, which can be described as a devastating disease. Its harmfulness is so great that it even affected the course of human history.

The world-wide shocking Irish famine is an example. In that year (1845-1846), the potato late blight ravaged Ireland, causing a complete crop failure and leading to the death (starvation) of about one million Irish people. Another one and a half million people left their homes, and unrest broke out frequently...

As a typical epidemic disease, potato late blight currently occurs in almost all potato-growing areas in my country.

Its occurrence and prevalence are closely related to climatic conditions. Low temperature (10℃-25℃) and high humidity (greater than 80%) are the conditions in which the disease is most likely to occur.

Taking the northwest region of my country as an example, rainfall increases in July and August every year, and the temperature difference between day and night is large. When there is continuous rain (or fog) and dew on the potato leaves, the occurrence and spread of diseases are more serious.

Under suitable conditions, potato late blight can sweep through an entire field within a week, causing a complete crop failure.

Phytophthora infestans is an oomycete that is commonly found in well-aerated freshwater and marine waters (often called water molds), as well as on land.

It belongs to the kingdom Trichomycetes, phylum Oomycetes, class Oomycetes, orders Peronosporales, family Pythium, genus Phytophthora in taxonomy.

Because oomycetes are similar to fungi in many ways (such as growing in hyphae form), they are often mistaken for fungi.

However, as the research on it continues to deepen, researchers have discovered that its cell wall is mainly composed of cellulose and glucan, which is very different from fungi (fungal cell walls are mainly composed of chitin), and to a certain extent determines the differences between the two in reproduction, biological characteristics, and ways of invading plants.

In addition, systematic evolution and related metabolic studies also show that oomycetes are a type of eukaryotes that are completely different from filamentous fungi.

In terms of genetic relationship, it is closer to some algae with chlorophyll a and c (such as diatoms and brown algae).

Phytophthora infestans is a semi-biotrophic pathogen. In the early stage of infection, it needs to colonize in living host cells, causing necrosis of host tissues. It will then continue to survive in the necrotic tissues and form spores.

Phytophthora infestans can infect potato leaves, stems and tubers, with the initial source of infection often being diseased plants left in the field or used as seed potatoes.

When it invades the plant, it forms branched mycelium between the host cells. These intercellular mycelium can produce finger-like suckers to invade the interior of the cells, causing necrosis of the host tissue.

When conditions are favorable, large numbers of sporangiophores (branched hyphae supporting the sporangium) form and emerge from the stomata on the underside of the leaves.

Subsequently, the sporangia on it can form and release a large number of spores. After these spores fall on the leaves of the host plant, they can germinate and form attachment cells, invade the epidermal cells, and start a new round of infection cycle.

Figure 1. Disease situation in the field (provided by the potato research group of Huazhong Agricultural University)

It is true that late blight is extremely harmful to potatoes. However, as the victim, potatoes did not sit idly by and wait for death, but evolved some secret weapons to fight against it.

For example, in some potato varieties resistant to late blight, the virulence factors (substances that constitute virulence) of the pathogen can be recognized by the host's disease resistance proteins, triggering a defense response.

In contrast, pathogens will try their best to evolve new virulence factors to evade host recognition.

Therefore, during the long process of evolution, potatoes and pathogens have been constantly engaged in an "arms race" for their respective survival.

Of course, breeders are also trying all kinds of ways (such as hybridization with wild disease-resistant varieties and genetic engineering breeding) to help potatoes take the lead, while ensuring their yield and quality, while meeting human needs.

How about it? Isn’t it interesting?

-END-

Editor: He Jiahuan

*This article was first published by "The Fat Devil's Microbial Front" (WeChat ID: nldxhjwswx). Any media reprinting must retain the name and WeChat ID of "The Fat Devil's Microbial Front". Any changes, including the title, are strictly prohibited without permission.

*Most of the pictures in this article are from the Internet. Please inform us if there is any infringement. Friends are welcome to correct the content, all for better science popularization!