One of the main factors that affect pepper production is the occurrence of diseases in different producing regions and with different etiological origins such as fungi, bacteria, viruses and nematodes.
In agricultural soils there is usually a complex community of different species of nematodes. Some feed on bacteria or fungi that are important in the decomposition and recycling of nutrients, others are predators or omnivores. However, a substantial portion of the soil nematode community feeds directly on plant roots, sometimes causing disease.
In the case of pepper cultivation, some species of nematodes pose serious problems for cultivation. They occur throughout the world where pepper is cultivated and have a wide range of hosts, mainly plants from the Solanaceae family.
The amount of damage caused by nematodes depends on a number of factors. Probably the most important is the species present in a given growing area. However, other factors also influence the losses caused in commercial pepper plantations, such as nematode population density, pepper cultivar, temperature and type of soil, fertility, crops prior to pepper planting and the agricultural practices adopted.
Worldwide, the greatest losses in pepper cultivation are attributed to the root-knot nematode (Meloidogyne). However, occasionally, other nematodes can be associated with the crop, such as Aphelenchoides, Aphelenchus avenae, Belonolaimus longicaudatus, Criconemoides, Helicotylenhcus dihystera, Paratrichodorus minor, Mesocriconema spp., Nacobbus aberrans, Pratylenchus penetrans, Pratylenchus brachyurus, Rotylenchulus reniformis, Radopholus similis, Trichodorus spp., Tylenchorynchus, Tylenchus and Xiphinema spp.
It is worth noting that in a soil sample from pepper crops there may be nematodes belonging to several genera and species. However, many do not cause significant harm or threat.
Root-knot nematode (Meloidogyne spp.)
The root-knot nematode Meloidogyne incognita It is one of the most important species that causes damage to pepper. It has a wide range of hosts, which mainly include solanaceous vegetables such as peppers, jiló, eggplant and tomatoes. M. unexplained It is present practically throughout the world, mainly in regions with a hot climate, including tropical and subtropical regions. However, other species such as M. hapla, M. javanica e M. arenaria they also occur in pepper crops (McSorley & Thomas, 2003). In vegetables, another species of root-knot nematode, M. enterolobii (without. M. mayaguensis), has been causing losses. This species was detected for the first time in Brazil parasitizing rootstock of Silver pepper and tomato plants resistant to meloidoginosis (cultivars Andrea and Débora) in the state of São Paulo (Carneiro et al, 2006) and represents a serious threat to peppers grown in the country.
Symptoms
Symptoms of infections caused by nematodes in the aerial part of plants include dwarfism, wilting, chlorosis (Figure 1), in addition to nutritional deficiency, reduced fruit size and consequently low crop yield.
Figure 1 - Chlorosis in the aerial part of plants Capsicum (A). When the plant is uprooted, the presence of galls on the roots is noted due to infestation by Meloidogyne sp. (B). (Photo: Ailton Reis)
Root-knot nematodes are endoparasites that, when penetrating plant roots, establish a feeding site and the formation of giant cells around this site. At the same time, galls form on the roots, which are characteristic symptoms due to penetration and infection by Meloidogyne spp. Generally, galls on pepper plants are much smaller when compared to galls that occur on other vegetables such as tomato (Figure 2).
Figure 2 - Galls on pepper roots (A) and galls on tomato roots (B) due to infestation by Meloidogyne spp. (Photo: Jadir Borges Pinheiro)
Egg masses (Figure 3A) ranging in color from brown to black above the galls can be visualized and, by drying these pyriform-shaped female roots, they can be extracted (Figure 3B).
Figure 3 - Mass of eggs above the surface of the galls on the roots (A) and females of Meloidogyne spp. (B) (Photo: Jadir Borges Pinheiro)
Plant stand failures in addition to the presence of reboleiras can occur in areas where population levels are high. Furthermore, roots severely damaged by root-knot nematodes can be invaded by fungi and bacteria that increase the damage and cause rot.
Lifecycle
The life cycle of root-knot nematodes begins with the formation of the egg (Figure 4), and during this cycle these organisms go through four juvenile stages before becoming adults. The first ecdysis or change of the cuticle (outer covering of the nematode's body) occurs inside the egg. Then the 2nd stage juvenile (J2) (Figure 4) hatches from the egg and goes to the soil, where it finds and penetrates directly into a root.
Figure 4 - Eggs at different stages of embryogenesis and 2nd stage juveniles Meloidogyne spp. (Photo: Jadir B. Pinheiro)
J2 are worm-shaped and measure around 0,3mm to 0,5mm, which may vary depending on the species of Meloidogyne. Only J2 of the root-knot nematode is infective and moves through soil particles in search of host plant roots. The juvenile generally penetrates through the growing tip (cap) and migrates between cells until it establishes a feeding site in the cells. At this point it becomes a sedentary endoparasite. Secretions produced by the nematode's esophageal glands stimulate the formation of several giant cells in the parasitized roots, which provide nutrients for the nematodes throughout the cycle. Nematodes rapidly increase in size and undergo ecdysis, transforming into 3rd (J3) and 4th instar (J4) juveniles, and finally into adults.
As adults, males migrate away from the root and do not feed.
During the cycle, a female produces hundreds of eggs, which can reach more than a thousand, depending on environmental conditions. These are deposited in a mass of eggs external to the roots, on the surface of the galls (Figure 3A), where they are trapped in a mucilage protected against desiccation and other adverse conditions.
The cycle of Meloidogyne spp., from egg to egg, takes three to four weeks in summer, which can be extended up to seven weeks in winter. Thus, the length of the life cycle is strongly dependent on temperature and increases as soil temperature decreases.
Root-knot nematode survival and completion of the life cycle depend on the successful growth of the host plant and environmental conditions.
Due to the fact that nematodes move slowly in the soil, where the distance covered during their life cycle probably does not exceed a few centimeters, their main form of spread is passive, caused by the movement of soil, water, contaminated agricultural implements, man and animals in cultivation areas and, mainly, by contaminated pepper seedlings. The latter is responsible for the contamination of areas over long distances.
Control
Prevention is the best way to control soil pathogens, especially nematodes, as it keeps the cultivation area free of these pathogens, once introduced, their eradication is practically impossible. Therefore, the main objective of the usual control methods is to reduce or maintain nematode population densities at levels that do not cause economic damage.
Planting pepper seedlings free of phytoparasitic nematodes in uncontaminated soil is essential to keep this group of pathogens out of the cultivation area, as the possibility of introducing these pathogens into the crop is drastically reduced (Figure 5)
Figure 5 - Seedlings Capsicum contaminated with Meloidogyne sp. Roots with numerous galls and egg masses (Photo: Jadir B. Pinheiro)
Care must also be taken to disinfect agricultural machinery and implements. These equipment, when dirty, can spread soil particles contaminated with nematodes, spreading this parasite in uncontaminated cultivation areas. Therefore, removing soil adhered to tires and other parts of machinery is efficient in reducing the spread of these organisms.
Furthermore, care with irrigation water is extremely important, as nematodes can be spread by irrigation water from contaminated sources.
Fallow
Fallowing consists of leaving the area without vegetation (crop or weeds) for an extended period, one or two years, so that the nematode population is reduced to levels below the economic damage limit. The soil must be kept free of vegetation with manual weeding, plowing, harrowing and the associated use of herbicides. Fallowing reduces the population not only of root-knot nematodes, but also of other species of these parasites through the action of sunlight. The efficiency of the fallow will depend on its duration, temperature, soil humidity and the species of nematode involved. It is recommended to leave a certain level of moisture in the soil, called wet fallow, allowing eggs to hatch and the movement of juveniles of the nematode species present. With movement, juveniles will consume more of their energy reserves and die from starvation. Despite the advantages, fallowing is a practice that has the disadvantage of cost. In addition to the expense of keeping the soil clean and without production for a certain period of time, erosion is encouraged in regions with high rainfall. Therefore, caution should be exercised when adopting the practice.
Elimination of tigueras and weeds
As well as crop residues, tigueras (crop plants that are born and develop involuntarily in the field) and weeds can also host nematodes common to peppers, serving as a source of inoculum for successive crops. Therefore, it is recommended to eliminate these plants by uprooting and destroying them, without incorporating them into the soil.
Solarization
This practice consists of covering the damp soil with a layer of transparent canvas, usually polyethylene (50µm to 100µm), allowing the entry of solar rays that heat the soil in the most superficial layers. This warming significantly reduces the population of nematodes and other soil pathogens, in addition to promoting partial control of weeds. Solarization efficiency and soil temperature are reduced as depth increases. However, positive effects are obtained with soil coverage for a period of three to eight weeks, conditions in which the soil temperature reaches 35ºC to 50°C up to 30 centimeters deep, depending on the type of soil.
The efficiency of solarization can be enhanced when associated with the incorporation of organic matter into the soil, before the start of treatment. Among the advantages of this association is the fact that the heat provided by solarization can accelerate the decomposition process of organic residues in the soil, increasing the temperature even further. Furthermore, with the decomposition of organic matter there is also an increase in the population of natural enemies of nematodes and the release of nematicidal substances that provide an increase in solarization efficiency.
crop rotation
Crop rotation is one of the most important practices recommended for reducing nematode inoculum in infested areas. Initially, it is necessary to identify the species of nematode to recommend a culture that is not a host. In cases of consecutive plantings with host plants, for two to three years, in the same area where there is an incidence of root-knot nematodes, there may be an explosion in the population levels of these organisms, thus making the area unviable for subsequent cultivation. However, rotation is quite difficult, as M. unexplained They have more than a thousand known host plant species. Furthermore, it has four different races (1, 2, 3 and 4) characterized by attacking different species of plants.
Crop rotation with non-host species of a given nematode aims to totally or partially eliminate these organisms by removing their food. Thus, in areas infested by M. unexplained rotation with some resistant corn and sorghum cultivars, brachiaria (brachiaria spp.), sunn hemp (Crotalaria spectabilis), castor (Ricinus communis L.) and other host plants. The greater the degree of infestation, the longer the rotation period should be.
Antagonist plants
The use of antagonistic plants has shown significant results in reducing nematode population levels in different crops. Crotalaria, marigold and mucunas are examples of antagonistic plants that are used to control nematodes. It is worth highlighting the fact that C. juncea and mucunas have proven effective for M. unexplained e M. javanica, as they are bad hosts, however, they can cause an increase in population densities in certain cases when conditions are favorable to the nematode.
Antagonistic plants may allow nematode invasion, however, they do not allow their development into adulthood. This is the case of sunn hemp, which function as hosts, attracting nematodes to the roots. However, in a second phase, they offer repellency to nematodes that penetrate or are in the vicinity of the roots. Thus, the formation of giant cells or nurse cells (cells responsible for feeding nematodes, formed after penetration and establishment of the site of infection) does not occur, inhibiting the development of juveniles. Sunn hemp also produce toxic substances, such as monocrotaline, which inhibits the movement of juveniles. It is recommended to cultivate sunn hemp for approximately 80 days, followed by the incorporation of the green mass, avoiding the beginning of flowering so as not to hinder the decomposition process due to the formation of a high volume of materials that are difficult to decompose. In the case of marigolds, alpha terthienyl and other substances with toxic action on nematodes are released. Antagonist plants, sunn hemp and mucunas can be used as a cover crop or incorporated into the soil in the form of green manure, also improving the physical and chemical conditions of the soil and incorporating natural fertilizers.
Use of organic material
Organic materials favor the vigorous growth of plants, enabling greater tolerance to nematode attacks. Furthermore, organic matter increases the population of soil microorganisms, especially natural enemies, in addition to releasing toxic substances to nematodes with their decomposition, contributing to their mortality. Organic matter works as a soil conditioner, favoring physical properties, in addition to contributing to the supply of nutrients, such as nitrogen.
Cattle or chicken manure, coffee straw, sugarcane bagasse, brassica residues and castor bean cake are examples of organic materials. Whenever possible, these materials should be sterilized before being applied, especially in new cultivation areas, as they can be a source of dissemination of phytopathogens.
resistant cultivars
Whenever possible, the producer should use cultivars that are resistant or tolerant to diseases. Among the main demands of pepper producers raised by extension agents and researchers in Brazil, the existence of pepper cultivars with disease resistance stands out (Reifschneider & Ribeiro, 2008).
The improvement of Capsicum in the search for resistance to nematodes plays an important role in their management. The use of resistant varieties, together with other cultural practices, is of great relevance for the control of nematodes, and has the advantages of not posing risks to human health, being relatively low cost and not polluting the environment.
In this context, Embrapa Hortaliças has been working since 2008, in its germplasm bank, in the search for sources of resistance to root-knot nematode. The results obtained so far are very promising, with the detection of sources of resistance to some species of Meloidogyne in launched cultivars and prospects for launching other resistant pepper varieties in the near future.
A BRS Sarakura pepper cultivar with resistance to M. unexplained race 1 and M. javanica (Figure 6) and five cultivars BRS Mari, BRS Moema, BRS Garça, BRS Brasilândia and BRS Seriema, all with resistance to M. javanica, have already been developed and launched by Embrapa.
However, these cultivars are susceptible to M. enterolobii. Therefore, the search for pepper genotypes resistant to this species, as well as the development and adoption of control strategies to avoid infestation of new areas, is essential, since in Capsicum spp., reports of damage caused by M. enterolobii have been more frequent each year.
Removal and destruction of cultural remains
Many nematodes remain viable in crop residues, serving as a source of inoculum for future crops. Therefore, removing infected roots from the area immediately after harvesting is a simple and important strategy for reducing inoculum in the area before the next planting. The root remains must be piled up and dried to finally be burned.
The maintenance and incorporation of infected remains of pepper roots in the cultivated area is not recommended, as it makes the usual control methods unfeasible, considering that nematodes housed in tissues of cultural remains become protected from the action of nematicides and other physical and biological agents. of control.
chemical control
There are currently no nematicidal products registered with the Ministry of Agriculture, Livestock and Supply (Mapa) for use on peppers.
Sampling for diagnosis
The diagnosis of the nematode species involved is made by analyzing soil and root samples, in a specialized laboratory, with the aim of knowing the quantity of these organisms in the soil, before planting and in later stages of crop development.
When collecting samples, small portions of soil, weighing 200g, and some roots make up each simple sample. It is recommended to collect around 15 to 20 simple samples (subsamples) per hectare. As you walk in a zigzag pattern through the suspected area, soil subsamples should be collected at depths of 20cm to 30cm around the plants. Then, the subsamples must be homogenized to form a composite sample (400 grams to 500 grams), which must be placed in a polyethylene bag, together with 200 to 300 grams of randomly collected roots. The composite sample must be identified and sent to a specialized laboratory. For large and irregular areas, it is recommended to divide them into quadrants and a composite sample should be taken from each quadrant. If it is not possible to send the samples on the same day, they must be stored and kept at temperatures between 10°C and 15°C, or left in the shade to prevent drying out, which makes correct diagnosis in the laboratory difficult.
Receive the latest agriculture news by email
Receive the latest agriculture news by email
