From the magazine: No. 3 2014
Category: In Focus
Boris Anisimov, Deputy Director All-Russian Research Institute of Potato Farming named after. A.G. Lorja
The article discusses phytosanitary requirements for viral and bacterial diseases, which must be strictly controlled within the boundaries of special potato seed production zones. Particular attention is paid to minimizing possible sources and vectors of infection, the use of effective methods for the prevention and control of phytopathogens within special zones for the production of original and elite seed potatoes.
Infectious diseases caused by pathogenic viruses and bacteria can lead to a sharp decrease in the quality of seed potatoes. There is a generally accepted pattern - the higher the level of infection load in places where seed potatoes are grown, the greater the likelihood of infection spreading through seed and through soil, and the more serious the harm that can be caused by these diseases [1].
In modern world practice, this problem is most successfully solved by creating special protected areas (zones) with favorable natural, climatic and phytosanitary conditions for growing healthy (free from phytopathogens) seed potatoes. The creation of such zones, in fact, becomes an integral part of modern systems of virus-free potato seed production [2,3,4,5].
Well known, for example, is the successful experience of creating and operating a special zone for growing seed potatoes of the highest quality category in Finland, in a region with a cool climate (Tyrnavä province), where more stringent standards for phytosanitary requirements have been introduced within this territory. Of great interest in this regard is the experience of Great Britain, where the most favorable phytosanitary zones have also been identified in the lands of Scotland and Northern Ireland, which have been assigned a special EU status "Territory for growing seed potatoes of the highest quality" (High Grade Seed Potato Region) [6,7].
In recent years, in certain regions of the Russian Federation, active work has also been carried out towards creating zones favorable for potato seed production, where stricter state phytosanitary control is established and special attention is paid to minimizing possible risks of the spread of infection through seed and through soil [2,3,4].
In modern practice of phytosanitary control within the boundaries of designated seed-growing territories, four groups of pathogenic objects are especially strictly controlled:
- diseases and pests of quarantine significance (potato cancer, brown rot, potato cyst nematode);
- phytopathogenic viruses transmitted by migratory aphid species (Y-potato virus (YBK - various strains), A-potato virus (ABK), M-potato virus (MBK) and potato leaf roll virus (PLV);
- viruses transmitted by soil-dwelling nematodes and fungi (Potato top panicle virus (“MOP-TOP”) and tobacco rattle virus (“RETTL” virus);
- pathogenic bacteria (“black leg” and ring rot of tubers).
Diseases and pests that have quarantine significance are considered especially dangerous, therefore the possibility of their spread through seed material and through the soil in places where seed potatoes are grown should be completely excluded.
Phytosanitary requirements for viral and bacterial diseases are regulated by the introduction of regulatory tolerances within the framework of current international and national quality standards for seed potatoes [8,9]. Most seed potato exporting countries generally have a zero tolerance for bacterial infections (Dickey/Pectobacterium spp., Clavibacter michiganensis). Infection of seed material with viruses carried by migratory aphid species is strictly controlled based on laboratory testing of tuber samples from direct offspring of classes SE (super elite), E (elite), A and B (1-2 reproductions after the elite) using fairly stringent regulatory requirements of standards (Table 1).
Table 1. Regulatory tolerances of standards for virus contamination of seed potatoes entering trade in the EU countries (ELIZA test)
Countries | Tolerances for classes/generations of seed potatoes, % | |||
SE | E1-3 | A1-2 | B | |
EC* | 4 | 10 | ||
UNECE** | 2-4 (1-2) | 10 (5) | 10 | |
Germany** | 4 (2) | 4 (2) | 8 (4) | |
Holland | 0,5 | 2 | 6 | 10 |
Finland*** | 0,5-1 | 4-10 | ||
France | 1 | 2 | 5 | |
Belgium | 2 | 3 | 6 | 10 |
Bulgaria | 0,5 | 0,5-4 | 8 | 10 |
The Czech Republic | 2 | 2-4 | 5-10 | 10 |
*According to EU Directives 2002/56 and 93/17
** The tolerance for YVC
***Tolerance for viruses YVK+AVK
The degree of potential risks of viral infection of potatoes largely depends on the natural and climatic characteristics of the territories. On the vast territory of Russia, potatoes can be successfully grown almost everywhere, but it is possible to produce high-quality competitive seed material only in conditions with the most favorable climate and minimal risk of the spread of pathogens of severe (acute) forms of viral diseases, especially wrinkled and banded mosaic (YBK) and necrotic ringspot potato tubers (YВКNTN) (Figure 1).
Fig. 1 Symptoms of severe (acute) mosaic (YBK) and ring spot of potato tubers (YBKNTN) [9].
Taking into account the wide variety of natural and climatic conditions, as well as factors that have the strongest impact on the quality of seed potatoes in the places of their production in the Russian Federation, globally we can distinguish three territories that have significant differences in the level of infection load and the total vector activity of insects that carry the infection .
Northern and northwestern regions are generally considered to be the most favorable for growing high-quality seed potatoes. Cool weather during the growing season, as well as a relatively low background of insect vectors, make it possible to minimize the spread of the most harmful viruses. The growing season in these regions is very short: from late May to mid-September (100–110 days). But the longness of the day, characteristic of northern latitudes, especially in the initial growing season, creates good conditions for rapid growth and development of plants, accelerated tuberization and crop formation. These conditions make these regions quite favorable for growing high-quality seed material.
The middle part of Russia, including the Central, Central Black Earth region, the Middle Volga region, as well as the Urals, Siberia, and the Far East, despite the wide diversity of climate and soils, is generally characterized by a relatively moderate background of the infectious load and can be considered as a territory quite favorable in phytosanitary terms for organizing your own production of seed potatoes in accordance with regulatory requirements of standards.
South and South-East regions less favorable for growing high-quality seed material. Due to the hot and dry growing season and, as a rule, a constantly high level of infection load and the total vector activity of insects that carry infection (with the exception of the mountain and foothill zones of the North Caucasus), the rate of increase in viral infections with each subsequent field generation is much higher than in areas located in more northern latitudes. The high rate of growth of viral infection reduces productivity and sharply deteriorates the seed quality of potatoes after the second growing season, and in susceptible varieties even after the first.
One of the fundamental principles of creating special seed-growing zones is the isolation of the location of land plots while maintaining the necessary spatial removal of healthy material from any possible sources of viral infection (planting food potatoes, vegetable gardens, cottages, etc.). For this reason, within the boundaries of special seed growing zones, it is necessary to ensure strict compliance with the minimum standards of spatial isolation for the corresponding categories and classes of original and elite seed potatoes. Based on modern ideas about the methods and characteristics of the transmission and spread of phytopathogenic viruses, as well as the migration of their carriers on potatoes, it is recommended to ensure a spatial distance from possible sources of infection for seed material of the primary stages of reproduction of 500 m, subsequent field generations of 100 m (Table 2)
Table 2. Standards of spatial isolation recommended for growing original and elite seed potatoes.
Category | Class | Insulation |
Raw material | Growing mini-tubers under protection from infectious vectors | Frame summer greenhouses with polycarbonate coating, covering tunnels made of lightweight covering materials |
Original seed potatoes | Field propagation (1-2 generations) | 500 m distance from any other seed potato classes |
Elite seed potatoes | Super elite and elite nurseries | Distance of 100 m from lower classes of seed and commercial plantings |
Typically, well-ventilated coastal areas located near seas and large bodies of water, fields located surrounded by protective-screening forest plantations, as well as arable lands located in mountainous areas are best suited as favorable environment-forming factors within the boundaries of seed-growing zones. It is important that the lands allocated for field nurseries be as far as possible from both the potato fields of industrial enterprises and the household plots of the population. Within the boundaries of an isolated seed-growing area, the possibility of spontaneous planting of potatoes should be excluded, especially in the gardens of the local population and summer cottages.
From a practical point of view, to create the most favorable environment in a special seed production zone, especially when growing primary field generations, a completely accessible and quite effective technique is “micro-isolation” using protective screening crops of grain crops or grasses along the edges of the field (Fig. 2).
Rice. 2. Scheme of micro-isolation of plantings of primary field generations using protective screening sowing of grain crops along the edges of the field.
In order to guarantee the quality of seed material in special seed production zones, it is strictly necessary to comprehensively use the most effective agricultural practices that limit the spread of viral infection in field conditions, including:
- compliance with established standards for spatial isolation of original and elite seed potatoes from plantings of lower reproductions;
- creating the most optimal conditions for rapid growth and development of plants and accelerated tuber formation during the growing season;
- carrying out regular phyto-cleaning with the earliest possible rejection and removal of infected plants from plantings, as possible sources of infection;
- the use of effective insecticides, as well as preparations of mineral and vegetable oils against aphids that carry viral infection;
- establishing optimally early terms for removing tops when achieving maximum seed marketability of tubers, taking into account the results of monitoring sources of infection and insects that carry viruses (migratory species of aphids) in the conditions of each specific farm;
- disinfection of storage facilities, equipment, machinery, containers before storing seed lots.
Within the designated seed-growing areas, seed material must be produced in strict accordance with established quality criteria for the categories and classes of seed potatoes produced.
Sources of input material within the boundaries of the designated areas should be limited to only those that meet standard quality criteria. It is permissible to use source material from several sources, but only if it meets established quality criteria. Healthy starting material must be produced in laboratories and greenhouses, which may be located outside the designated area.
After the development of the territory, only the seed material that is produced within its boundaries should be used in its area in the future. Planting of material produced outside the site is generally not permitted. In this regard, it is especially important to ensure proper control over citizens’ gardens and, if necessary, organize the supply of high-quality seed potatoes for the needs of local gardeners and summer residents. In practice, this is only possible on the basis of voluntary participation on the part of the local population and the interest of citizens in the gradual replacement of their old local seed material with a new one, which is produced within the boundaries of the controlled seed-growing territory.
One of the key elements of a special technological production regime within the controlled territory is the introduction of a special inspection system, which should combine regular field phytosanitary surveys and laboratory testing of seed material using leaf and tuber samples. Strict adherence to standard laboratory testing standards and methods for the relevant classes/generations of seed potatoes must be ensured. Thus, in the initial invitro material intended for clonal micropropagation in laboratories, 100% of plants are tested by ELISA and PCR analysis. When growing mini-tubers in greenhouses, a minimum of 250 plants from each variety are tested by ELISA. In the first field generation of mini-tubers, 200 plants per plot of each variety are tested by ELISA (or 200 tubers in a post-harvest tuber sample). In a post-harvest sample from the super-super elite crop, 200 tubers from each batch are tested by ELISA. On super-elite and elite potatoes, in addition to visual inspection of plants, during field surveys, plants with insufficiently clear manifestations of disease symptoms are checked using immunodiagnostic methods.
The introduction of an inspection system combining field phytosanitary inspections and mandatory laboratory control of the highest categories of seed potatoes within the boundaries of special seed-growing zones should become an integral part of the technological regulations for the production of original and elite seed potatoes.
In solving the problem of creating special zones for potato seed production, certification of agricultural land by conducting surveys to identify pests, diseases and weeds with the subsequent issuance of phytosanitary passports of the fields can be important. The presence of phytosanitary passports of fields is one of the requirements for voluntary certification of individuals and legal entities engaged in the production (cultivation), processing (preparation), packaging and sale of seeds of the highest categories
Bibliographic list
1. Anisimov B.V. Phytopathogenic viruses and their control in potato seed production (practical guide) - M.: Federal State Scientific Institution "Rosinformagrotekh", 2004. - 80 p.
2. Anisimov B.V. Phytosanitary zones and their role in virus-free potato seed production // Plant protection and quarantine. 2014, No. 11, p. 14-19.
3. Anisimov B.V. Potato seed production at altitude // Potatoes and vegetables. 2014.No.8. p.29
4. Anisimov B.V. Special zones for potato seed production // Potatoes and vegetables. 2015. No. 4. pp. 34-37.
5. Recognition of pest free areas and areas of low pest prevalence. Rome, FAO = ISPM 22:2005. Access mode: https://www.ippc.int/core-activiities/standards-setting/ispms.
6. The Seed Potatoes (Scotland) Amendmtnt Regulations 2000 no. 201.= (date of entry into force 01.04.2006). Access mode: https://www.legislation.gov.uk - Language: English, Russian.
7. The Seed Potatoes (Scotland) Amendment Regulations 2010 no. 71.= (effective date: 1.07.2010) Access mode: https://www.legislation.gov.uk/-
8. UNECE Standard S-1, Concerning the marketing and commercial quality control of seed potatoes. UNITED NATIONS, new York and Geneva. 20B.- 41 p.
9. UNECE Guide to Seed Potato Diseases. Pests and Defects. United Nations. Economic Commission for Europ, Specialized Section on Standardization of Seed Potatoes .Geneva, 2014. –108p.