Late Blight of Potato

Late blight is a deadly fungus that damages potatoes. It is available all around the world. It can be found in potato-growing regions around the world. In India, the main potato-growing season is winter. In the plains, it is followed by hot summer months. The fungus in the soil is killed by dryness and high temperatures. Before discussing the details and the blight meaning let us look into the causative agents. The Late blight of potato is caused by the fungus Phytophthora infestans, which is now the most common crop pathogen, which can cause crop failure in a short amount of time if effective control precautions are not taken. In epidemic years, declines in potato crops can reach as high as 80%.

The article discusses the causes of the late blight of potato which includes blight meaning, causes and symptoms, the article also discusses the management techniques of the late blight of potato.

Symptoms of Late Blight 

Late blight of potato is caused by a fungus known as  Phytophthora infestans, the blight symptoms are found in both potato stem and tuber.  The blight is also found in potato leaves. On leaves, late blight symptoms emerge as irregularly shaped dark dots that expand as the illness progresses. During damp environments, a pale green border typically envelopes the necrotic area just on the top portion, while whitish spore-bearing mould forms all around lesions on the bottom side. P. infestans generates sporangia and sporangiophores mostly on top of diseased tissue in damp environments and the whitish sporulation that results can be observed along the edges of lesions on the abaxial (bottom) regions of leaflets. 

The late blight of potato tuber is a darker brown, sometimes a purplish patch on the tuber surface marks as a symptom of tuber infection. Internal rot is a granular reddish-brown rot that might stay close to the surface or spread to the centre of the tuber. Rot spreads in a zigzag pattern through the tuber flesh, sometimes threadlike. Late blight damages the skin, allowing opportunistic germs to infiltrate and produce soft rotting. When sporangia are washed away from leaf lesions and enter the soil, potato tubers can become infected in the field. Infections usually begin with nodules, eyes, or lenticels. Infected tuber tissue is generally found in copper-brown, reddish-coloured, or purple. Spore formation can appear on the surface of infected tubers during storage or on the discarded extermination heap. Infected tubers are often attacked by Pectobacterium carotenoids, which require immediate conversion of adjacent healthy potatoes into odorous rotten masses for disposal.

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Why Late Blight is Considered Among Epidemic Potato Diseases?

The severity of the disease's effects is often extreme. The growth cycle is shortened when the vegetation is severely damaged.  As a result, the potatoes retain a small and compact mass. They are produced in minimal quantities. As a consequence, productivity is diminished. The infection leads to the total destruction of the harvest in extreme situations, as well as the rotting of tubers inside the field and during stockpiling.

Following infections, the bacteria can proliferate at a fast pace, as noticeable signs might develop in a short space of time. If contaminated potatoes are brought into a store, the illness can spread and cause massive losses. In GB and elsewhere, there are several strains ("varieties") of P. infestans that vary in the extent of disease they produce (proactivity) and its fungal susceptibility. Alteration in such traits has the potential to exacerbate the disease's severity and render its treatment extremely challenging.

Pathogen Biology of  Potato Diseases: Late Blight Disease

As we have discussed the late blight of potato is caused by fungus and late blight infection, blight meaning, symptoms and impact, let us look briefly into the causative agent of this commonly found disease. The late blight of potatoes is caused by Phytophthora infestans which is a member of Oomycete, a group of organisms sometimes called water moulds,  a fungus-like microorganism.  Oomycetes are associated with brown algae, not real mushrooms. One of the characteristic features is that the mycelium is a vitreous, polyploid. Other members of the Solanaceae family can also be infected by the bacterium. The nucleus of the pathogen is diploid, hence it can follow both sexual and asexual modes of reproduction. The diploid life cycle shares many biological, ecological and epidemiological properties with fungal plant pathogens.

Moist and cold settings are ideal for the pathogen. In water-saturated or nearly saturated settings, sporulation is best at about 12–18 °C, or approximately (54–64 °F). Temperatures below 15 °C (59 °F) are favourable for zoospore formation. At a slightly warmer temperature range of 20 to 24 °C, lesion development rates are normally excellent.

Late Blight of Potato Life Cycle

Infected seed potatoes planted are the disease's principal source. Only a handful of the contaminated tubers produce primary sporangial mycelium, which infects neighbouring plants and creates a major disease focus in the field. Some infected tubers might not sprout or are dead soon after sprouting, resulting in a patchwork appearance in the field. The heaps of culled contaminated potato seed accumulated beside the cold rooms additionally act as a critical reservoir for inoculum again for fields nearby. The accumulation of these contaminated seeds provides an environment for the growth of the disease under favourable conditions, which includes high moisture and low temperature. Since we have understood the basics of the infection pathway let us look into the late blight of the potato life cycle summarized in the following points.

• Sporangia may be developed on diseased tubers or potato stems if they are left behind during harvest or thrown at the boundaries of fields.

• The potato stem or tuber represent a source of primary inoculum if cultivated in the following agricultural season.

• The pathogen colonises several of the emerging sprouts and sporulates producing the sporangia under high humidity. These sporangia help transmit the disease.

• It usually takes 3-7 days for the disease to begin to display evident symptoms. One such symptom is on the underside of the leaves, the fungus develops white sporulation that is easily visible.

• The cycle of infection by sporangia repeats every 4-10 days, depending on the temperature and humidity levels in the area.

• Sporangia infect tubers in the soil when it is washed away by rain or brought by irrigation water. Tubers that have been partially exposed can readily become infected.

• The principal source of inoculum for the next crop batch is these diseased tubers.

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Management of the Disease

Some of the most important techniques for management of the late blight of potato disease include the following:

• Selection of disease-free tubers for planting.

• The potato tubers must be stored at a cold temperature.

• Development of infection resistant strains of the crops.

• Use of optimal fungicide.

• Sanitation in the storage area.

• Potato tubers must be treated with 1:  1000  mercuric chloride solution for  90  minutes prior to storage. This helps in inhibiting the growth of mycelium.

In conclusion of the article, we have learnt about potato blight, blight meaning, the causative agent of the disease. We have also learnt about the symptom, disease cycle and preventive measures for potato blight disease.