Maria Erokhova, junior research fellow All-Russian Research Institute of Phytopathology, e-mail: maria.erokhova@gmail.com
Maria Kuznetsova, Head of the Department of Potato and Vegetable Diseases of the All-Russian Research Institute of Phytopathology, Candidate of Biological Sciences
In the conditions of intensification of agriculture and international trade within the framework of the WTO, stem nematodes of the genus Ditylenchus (D. destructor, D. dipsacci) are recognized as one of the most dangerous pests for crops. In many countries D. destructor и D. dipsacci received the status of regulated pests: in the Russian Federation and the EU, they have the status of regulated non-quarantine pests (RNQPs) on seed potatoes [19, 18]. In accordance with international rules, the presence of RNQP status allows standards of different levels to establish tolerances (limits above which the presence of a given pest in lots of seed potatoes is not allowed). For example, according to the requirements of the national standard for Scotland, zero content tolerances are set D. destructor in all categories of pre-basic and basic potatoes on a par with many quarantine pests [11] due to the fact that the region has the status of a High Grade Region for the cultivation and sale of pre-basic and basic seed potatoes and operates to stricter standards than prescribed by the EU.
The scale of distribution of phytopathogenic nematodes of the genus Ditylenchus in countries with different levels of development of potato growing, of course, they differ. In some countries, stem nematodes occur in small numbers, in others, partly due to monoculture, the use of contaminated seed and planting material, they are a serious problem. Thus, in accordance with the data of the EPPO Global Database, obtained from scientific publications of Soviet authors [15, 21, 12, 22, 23, 16] and the International Center for Agricultural and Biological Sciences of the Member States of the British Commonwealth (CABI), in the days of the USSR on the territory of the Russian Federation D. destructor had the status of a widespread pest [18]. And to date, the situation has not changed [7]. In the UK, according to the NPPO, the status D. destructor – “present, in low abundance (few detections)” [5]. Concerning D. dipsacci, then according to information from the same sources, it occurs in Russia, but there is little information about it, in the UK, on the contrary, it is ubiquitous [18].
According to the EPPO Global Database D. destructor is a broad polyphage: the main host plant is potato (Solanum tuberosum)in addition, the pest causes significant damage to garlic (Allium sativum), beetroot (beta vulgaris), carrot seed (Daucus carota subsp. sativus), codonopsis small-haired (Codonopsis pilosula), crocus (Crocus), dahlia (Dahlia, gladiolus (gladiolus), hyacinth (Hyacinthus, Dutch iris (Iris × hollandica), peacock tigridia (Tigridia pavonia), clover (trifolium), tulip (Tulipa [eighteen]. According to CABI, the range of affected host plants D. destructor even wider: onion (Allium cepa), underground peanut (Arachis hypogaea), sugar beet (Beta vulgaris there. saccharifera), tea (Camellia sinensis), Sweet pepper (Capsicum annum), garden chrysanthemum (Chrysanthemum morifolium), common watermelon (Citrullis lanatus), Orange (Citrus), melon (Cucumis melo), common cucumber (Cucumis sativus), pumpkin nutmeg (Cucurbita moschata), garden strawberry (Fragaria in pineapple), soybeans (Glycine max), common hop (Humulus lupulus), sweet potato (Ipomoea batatas), mint (Mentha), ginseng (Panax ginseng), ginseng pentaphyllum (Panax quinquefolius), tomato (Solanum), eggplant (Solanum melongena), soft wheat (Triticum aestivum), cultivated grapes (Vitis vinifera), corn (zea mays)[fourteen]. Besides, D. destructor infects weeds: white gauze (Chenopodium album), full round (Cypress round), dope ordinary (Datura stramonium), goose grass (Eleusine indica), couch grass (Elymus repens), medicinal fumes (fumaria officinalis), black nightshade (Solanum nigrum), field thistle (Sonchus arvensis), small marigolds (Tagetes minute), dandelion officinalis (Taraxacum officinale), common cocklebur (Xanthium strumarium) [14]. It is noted that the range of host plants can be expanded as additional information becomes available [18].
According to the EPPO Global Database, the number of host plants forD. dipsaci is also extremely large [18]. For this reason, vegetable rotation may not be effective in reducing nematode populations.
Based on morphological, biochemical, molecular and other studies D. dipsaci sl divided into several groups [6]: economically significant of which are D. dipsaci sensu stricto и D. gigas n. sp. (the latter is found on common bobs (addictive faba) in many European countries) [17]. It is noted that in the case of the presence of highly specific races D. dipsaci a three-year crop rotation with resistant crops can reduce its numbers, provided that timely measures are taken to combat weeds that are alternative host plants [10].
Plant nematodes of the genus Ditylenchus are harmful organisms for plants, transmitted with seed tubers and bulbs of agricultural crops [14]. The source of infection is contaminated soil, wooden containers, and packaging material [14]. For short distances, the pest can spread along with irrigation water or raindrops carried by the wind to neighboring infected fields [14].
Stem nematodes are endoparasites living inside plant tissues (roots, tubers, rhizomes, bulbs) [10, 14]. Both males and females destroy cell walls during their feeding [10]. According to British scientists, fertility D. dipsacci can reach 500 eggs per female [10]. The stem nematode can persist mainly as fourth instar larvae for several years [10]. Adults and eggs are able to overwinter in the soil or in the tissues of weeds [14]. In spring, larvae hatch from eggs, which immediately colonize suitable host plants; pests penetrate potato tubers through lentils [14]. It is noted that the nematode can feed on the mycelium of many fungi, including Alternari a alternating и A. solani [fourteen]. Fourth instar larvae D. dipsacci (Unlike D. destructor) to survive in adverse conditions form clusters on the surface of infected plant tissue (the so-called "nematode wool") [10]. Nematodes become active again after the “wool” gets wet [10]. In wet soils, they can persist in the absence of host plants for more than a year [10].
Symptoms of pest damage are quite diverse.
As a rule, it is practically impossible to determine that a plant is affected by a nematode from the aerial parts of a potato (except for the fact that weak plants are formed from severely affected tubers, which may subsequently die) [14]. An early nematode attack can be detected by removing the skin from the tuber, under which it is easy to see small whitish spots in the healthy flesh. Later, these spots increase, darken, and the tissue acquires a loose texture [14]. If the tubers are stored in humid conditions, they rot and the nematode infection is transmitted to other tubers.
On severely affected tubers, slightly depressed areas are formed, on which cracks form, and the peel is wrinkled, strongly adjacent to the pulp [14]. The flesh becomes dry, changes in color: from gray to dark brown or even black. The color change is mainly due to secondary pathogens (fungi, bacteria and free-living nematodes) [14].
At defeat D. dipsaci cracks do not form on the tubers, but dark-colored rot spreads through the flesh inside. The tops are shortened and deformed.
The nematode also causes serious damage to other crops.
In the affected seedlings and young onion plants, the base of the stem swells, the leaves are bent and twisted [10]. The tissue affected by the nematode has a loose texture [10]. Plants rot at ground level. Weak damage to plants by a nematode may go unnoticed, but such bulbs gradually rot in storage.
The tissues of affected sugar beet seedlings swell and acquire a spongy texture [10]. Galls may form, at the points of growth, the tissue is deformed or dies, causing a curvature of the apex and the formation of small leaves. In autumn, the galls rot due to secondary pathogens.
Bean damage usually manifests itself as stem discoloration [10].
In oat plants, the base of the stem swells, the leaves turn pale, curl and shorten.
Determined that D. destructor causes the greatest harm at a temperature of 15-20 °C and relative humidity above 90% [14].
It has been proven that stolons and roots of potato plants are more actively affected by the stem nematode. rhizoctonia solani [14]. Also, according to preliminary data from ongoing studies, it was found that the presence of nematodes in the soil causes a tenfold increase in the number of bacteria that cause the black leg of the potato, thereby increasing the likelihood of developing the disease. Bacteria enter the plant through wounds caused by nematodes [9].
To reduce the harmfulness of stem nematodes, it is important to implement a set of techniques as part of an integrated plant protection strategy, relying primarily on the use of healthy (free from the pest) seed and planting material and the use of long crop rotations.
For soil disinfection with soil pathogens, phytonematodes and weeds, it is recommended to sow, grind and incorporate biofumigating crops into the soil (sarepta mustard (Brassica juncea), common radish (raphanus sativus), arugula (Eruca sativa) [1]. Isothiocyanates, formed during the destruction of the cells of these plants, inhibit cellular respiration and other functions, primarily in potato cyst nematodes. They provoke the release of larvae from eggs, cysts in the absence of a suitable host plant. Larvae, not finding a suitable host plant, die. The technology for growing and using biofumigating crops is described in the Russian-language literature [5, 1].
As for the use of the chemical method, in many EU countries, the permission for Vidat (a.i. oxamil) as a nematicide and insecticide is valid until 31.01.2023/20/10 [4,4]. According to the EU Database, it is recommended to plant the drug granules to a depth of 5,0 cm at a dose of 20-0,01 kg/ha, depending on the type of soil [20]. According to European data, the maximum allowable content of oxamyl residues in potatoes is XNUMX mg/kg [XNUMX].
English scientists suggest using Nematorin 10 G (a.i. phosphiazat) and Velum Prime (a.i. fluopyram) as alternative nematicides [1]. It is reported that Nematorin 10 G is used against potato cyst nematodes and free-living nematodes belonging to the pp. Trichodorus и Paratrichodorus, which are carriers of the tobacco rattle virus [1]. In the EU pesticides database, phosphiasate has already been registered in many EU countries (from 01.01.2004/31.10.2022/20 to 3/20/0,02) as a nematicide against cyst nematodes and gall nematodes [20]. According to EU recommendations, the minimum application rate of phosphiazat is XNUMX kg/ha when planting in spring [XNUMX]. According to European data, the maximum allowable content of residual amounts of phosphiasate in potatoes is XNUMX mg/kg [XNUMX]. In Russia, this active substance has not yet been registered.
In the United States, the registration of the drug Velum Prime is reported, which is intended to suppress phytoparasitic nematodes, as well as many diseases: white rust, alternaria, powdery mildew and verticillium. Fluopyram is a FRAC group 7 fungicide. In the EU database, fluopyram is registered as a fungicide [20].
According to the EU pesticide database as a nematicide on cucumber and carrots from 01.10.2013/30.09.2023/XNUMX to XNUMX/XNUMX/XNUMX. registered bacterial preparation Bacillus firmus I-1582 [20]. On cucumber and carrots Bacillus firmus I-1582 does not establish the maximum allowable content of residues and the waiting period [20], which allows us to consider it as a prophylactic used in the cultivation of vegetable crops in protected ground and, possibly, for the production of organic products and the production of baby food. In Russia, this drug is not yet registered.
The mushroom is also registered in the EU Purpureocillium licacinum strain 251 [20]. The use of the drug is allowed from 01.08.2008/31.07.2022/20 to XNUMX/XNUMX/XNUMX. in several EU countries on a number of crops in protected and open ground [XNUMX]. On potatoes, it is recommended to combat Pratylenchus spp., with CCN (balloon spp.) [20]. The technology of introducing the drug into the soil is rather complicated, and the effectiveness of the fungus action depends on the environmental conditions [20].
It is important to remember that there are no potato varieties resistant to stem nematodes of the genus Ditylenchus.
Summarizing the above, it can be concluded that the main methods for controlling the stem nematode on potatoes as part of an integrated protection strategy are:
— use of healthy seed potatoes;
- the choice of a long rotation of crop rotation, which allows to reduce the infection of the field with the stem nematode. It should be taken into account that some cultures can be strongly affected by various types of nematodes of the genus Ditylenchus, for example: red and white clover, garlic and onions [13];
- control of weeds and "volunteer plants" of potatoes: many types of weeds serve as alternative host plants for the nematode;
- disinfection of containers, equipment and potato stores with accepted disinfectants. The range and regulations for the use of these agents are given in the Russian-language literature [2], as well as in the standard of the European and Mediterranean Plant Protection Organization (EPPO) in a translated version [3].
– biofumigation of the soil with biofumigating crops from the cruciferous family (mustard sareptskaya (Brassica juncea), arugula (Eruca sativa), common radish (Raphanus sativus) [1].
- application of calcium fertilizers during planting and during the period of mass tuber setting, since sufficient calcium supply of agricultural crops contributes to the formation of a dense plant cell wall, which makes it difficult for the nematode to penetrate the plant, and also increases the resistance of potatoes to injury and bacterial blackleg [4].
- control of the degree of contamination of the soil with a stem nematode (before sowing and planting crops, it is recommended to analyze the soil in the laboratory). In the case of a severe infestation, such a field cannot be used to grow crops susceptible to the stem nematode. To reduce its contamination, it is recommended to use nematicides - as part of integrated protection, in compliance with the rules for the safe handling of pesticides. In addition, it is necessary to properly and timely dispose of the remains of nematicides and their containers, preventing contamination of irrigation and surface waters. Proper use of nematicides will reduce the negative impact on soil and water micro- and macrobiota.
Photo by Maria Kuznetsova, VNIIF
Photos validated by the British Commonwealth International Center for Agricultural and Biological Sciences (CABI) and posted in the CABI Compendium of Invasive Species (14)
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