Despite significant progress in the study of potato late blight and the implementation of control measures based on knowledge of the phytopathogen, the disease still causes significant damage due to crop losses and the cost of chemical treatments with plant protection products.
This disease is caused by an oomycete Phytophthora infestans, affecting leaves, shoots and tubers.
Tubers entering storage even with a small amount of infection often lead to large product losses. The causative agent of late blight remains viable even at a temperature of + 3° C. The development of the phytopathogen on the surface of tubers facilitates the penetration of opportunistic bacteria through the skin, causing soft rot.
Late blight symptoms on the leaves appear as irregularly shaped spots, which gradually increase in size as the disease develops. A light green border forms on the upper side of the leaves along the edges of the spots. On the underside of the spots along the edges in wet weather, sporulation of a white phytopathogen develops. On the surface of the tubers, the disease appears in the form of dark brown spots. A dark brown rot forms inside the tubers, located closer to the surface, but which gradually penetrates into the center of the tubers. The main route of spread of the phytopathogen is through airborne zoosporangia from infected fields, 'volunteer potato plants' and plants grown on piles of discarded tubers near fields. Plants grown from discarded tubers, like “volunteer” ones, can also be reservoirs of viral diseases transmitted by aphids; other diseases (rhizoctoniosis, anthracnose, powdery scab) and pests (free-living nematodes, potato cyst nematodes, aphids). In addition, oospores can form in them, which can further complicate the fight against late blight due to the increased risk of resistance with an increased number of fungicide treatments.
In the southern regions, to prevent the germination of culled potatoes, heaps must be promptly treated with diquat or glyphosate (if plants appear, the treatment must be repeated). A very effective method of combating such plants is to cover the discarded tubers with black film. Along the edges of the heap, the film must be well secured so that the zoosporangia of the phytopathogen cannot fly away, and animals cannot penetrate under the film and tear it. If the pile is covered with film early, glyphosate treatment may not be necessary. It is very important that the culled tubers are kept away from the potato field and sources of water for irrigation.
Most common for Phytophthora infestans is asexual reproduction, in which zoosporangia can germinate directly as hyphae or release zoospores with flagella, which penetrate the plant through the water film. Oospores can survive for a long time in the soil. For example, according to Dutch experts (Plant Pathology journal, 2000), oospores can retain their ability to infect potatoes in sandy soil for 48 months, and in clay soil for 34 months when flooded. It was noted that the largest number of oospores was formed in potato varieties with a low level of race-specific resistance. According to data from the European database Best4Soil (2020), to reduce soil infection Phytophthora infestans (oospores), potato cyst nematodes, rhizoctonia and other pests, it is recommended to return potatoes to the field after five years.
Until recently, the potato protection strategy was based on the use of a large number of treatments with plant protection products. But recently, partly due to the emergence of new resistant genotypes Phytophthora infestans (in a number of European countries, genotype EU_43_A1, resistant to mandipropamide at doses of 100 ppm), integrated potato protection has become more widely used.
Basic methods of integrated potato protection against late blight:
- Growing potato varieties with a high resistance score.
- Destruction of primary sources of infection (“volunteer” plants, piles of discarded tubers, infected seed tubers and affected potato plants).
- Using fungicide treatment decision systems based on late blight risk, variety resistance and weather conditions to plan the optimal number of plant protection treatments as part of an anti-resistance strategy. A program in Russian has been developed on the basis of the All-Russian Institute of Phytopathology (VNIIF) VNIIFBlight. FGBNU VNIIF has a patent RU 2019663121 (2019) for the computer program “Express forecast - late blight” for obtaining an online forecast of the development of late blight in the Russian Federation. Currently in Russia there is a decision-making system (DMS) for carrying out fungicide treatments against late blight and Alternaria "Agrodozor". Many other countries have also established programs to adopt late blight risk forecasting. For example, in the UK there is an online platform for late blight Hutton BlightSpy. The platform is maintained by James Hutton Limited, meteorological data is provided by the Met Institute and is covered by a Creative Commons Attribution 4.0 International License. In a number of regions, resources/platforms have been developed as part of the research work of specialists on monitoring population structure and the level of resistance to plant protection products (for example, in Europe - Euroblight, in China - ChinaBlight), information from which allows practitioners to apply plant protection solutions taking into account the structure of the pathogen population in the region and its level of resistance to fungicides. On the platform of the European consortium of specialists and organizations for the study of potato late blight Euroblight tables are maintained with the results of tests of active substances to combat late blight on different parts of the plant and Alternaria.
- Destruction of late blight-affected tubers in storage in order to reduce tuber losses and reduce the amount of seed infection for the next year.
Maria Erokhova, researcher, FGBNU VNIIF
e-mail: maria.erokhova@gmail.com