The great Irish Famine, also called Irish Potato Famine or the Great Hunger, happened in Ireland in the 1840s when the potato crop failed in successive years. The infestation ruined to one-half of the potato crop in 1845 and three-quarters of the crop over the next seven years. The famine was caused by late blight, a devastating potato disease that destroys both the edible roots and leaves of the potato plant. Scientists discovered that the causative agent of such disease is the algae Phytophthora infestans. Today, late blight remains as one of the most serious threats to potato production and causes economic losses globally.
Analyzing the late blight resistance response of wild potato
A new study conducted by Jiayi Zheng from the Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, and team discovered the novel resistance genes in diploid (cell) wild potato JAM1-4 (S. jamesii). The further transcriptional analysis shows the important role of secondary metabolic pathways and multiple signal transduction pathways in plant immunity. The team said that they used RNA-Sequencing - a technology-based sequencing technology that uses next-generation sequencing (NGS) to reveal the quantity and presence of RNA in a biology sample at a given moment – to analyze the late blight resistance response genes as well as the defense regulatory mechanism of wild potato.
Co-author Guangcun Li told Phys.org that the observed resistance in the wild potato they experimented with was due to previously uncharacterized novel resistance genes. They likewise discovered that to promote an immune response in the plant, photosynthesis was inhibited. The scientists also said that the physical barrier of leaves in wild potato is important.
The leaves of the wild potato they tested show immunity when injected with pathogens at low concentrations. The leaves are also hard, which forms a physical barrier against infection. The result of their study can serve as a new theoretical basis for disease resistance breeding, which is an important strategy for reducing crop losses.
Major changes are happening in the world potato sector. According to the Food and Agriculture Organization and the International Potato Center, the top potato producers in 2007 were China (79,410,500 tons), Russian Federation (40,547,600), India (28,968,700), United States (22,457,700), and Ukraine (21,056,400).
In South Korea, potato production reached 553,596 tons in 2018. In the US, it was 20.61 million tons and in Ireland 273,000 tons.
The Irish Potato Famine
History.com explains that when crops started to fail in 1845 in Ireland, Irish leaders petitioned the Parliament and Queen Victoria to act since potato was a staple food of the poor, especially during the cold winter months. The leaders acted initially, repealing their tariffs on grain and their Corn Laws. The tariff made food, such as bread and corn prohibitively expensive. However, the offset failed to change the growing problem of the late blight.
At that time, many tenant farmers were still unable to produce sufficient food for their consumption and the costs of other supplies were also increasing. Thousands of people died due to starvation and hundreds of thousands more from a disease that was also caused by malnutrition.
Historians have concluded that during the blight, Ireland continued to export large quantities of food, mainly to Great Britain. A study suggests that exports of butter and livestock may have increased during the Irish Famine. In 1847, commodities, such as rabbits, honey, fish, beans, and peas also continued to be exported from Ireland even if it was ravaged by Great Hunger. It was until 1852 that the potato crops fully recovered but by then, the damage was done. People perished and about a million emigrated to escape starvation and poverty. In recent years, some cities in the US, Canada, Ireland, Great Britain, and Australia erected Irish hunger memorials.
Signs and symptoms of late blight
The University of Minnesota Extension, which was not involved in the study, has identified the signs and symptoms of blight. It includes large, dark brown blotches in the leaves of potato with a green-gray edge. The blotches are not confined by major leaf veins. The infections progress through petioles and leaflets, resulting in large sections of dry brown foliage. Stem infections are dark brown and firm with a rounded edge.
Another sign of blight is that in high humidity, thin powdery white fungal growth appears on infected stems, fruit, and leaves. If left unmanaged, the disease can potentially destroy an entire field in a short time. As part of cultural control, the University suggests destroying the potato cull piles before the start of the growing season. This is done by burying, incorporating, or spreading them into the fields or feeding them into animals. It is also important to control volunteer potato plants because infected plants can grow from the infected tubers. Under wet and cool conditions, the P. infestans can infect potatoes and produce thousands of sporangia per lesion in less than five days, it added.
If the infection is observed only in a few plants within a field, infected plants need to be disced-under, removed, and killed with flame or herbicide to avoid spreading through the field. Some growers have also used chemical control.
Today, potato is still an important global cash crop and food. Based on a comparison of 154 countries in 2017, investment management firm Helgi Analytics found that China eats the most potatoes 61,980 metric kiloton (kt), followed by India, USA, Russia, Bangladesh, UK, Ukraine, Germany, Iran, Poland, and Turkey.
Another plant pathogenic virus that affects potato production is the Potato virus Y. Potato plants infected with potato virus Y may show several symptoms, depending on the potato variety. Studies have shown that some strains of the potato virus Y can cause necrotic symptoms in tubers. An example strain would be the PVYN. The letter N stands for necrotic. The potato leafroll virus can also cause foliar symptoms. It causes the leaves of the potato to become chlorotic and pale. Some potato varieties are more susceptible than others and some may be infected without showing symptoms.
For all potato growers, planting disease-free potato seed is important, no matter the size of the acreage. The recent findings of the novel resistance genes in potato can be of tremendous help to growers for successful plant breeding.