Carrot crops are affected by different pathogens, which often make production unviable. The phytonematodes responsible for large losses in cultivation stand out, constituting a constant concern on the part of producers and interest for researchers.
Nematodes of the genus Meloidogyne they have a wide range of host plants, including more than two thousand susceptible plant species, including several vegetable crops, such as pumpkin, lettuce, eggplant, carrot, cucumber, tomato, pepper, pepper and others.
Knowledge of the occurrence of these pathogenic agents allows the adoption of joint measures, mainly preventive, helping the producer to reduce damage to the crop. The occurrence of these pathogens is not limited to the main producing states such as Minas Gerais, São Paulo, Paraná, Bahia and Rio Grande do Sul. It also finds favorable conditions for its development in the northern region of Mato Grosso, causing total losses in areas commercially cultivated with carrot.
Root-knot nematodes (Meloidogyne spp.) represent one of the main problems phytosanitary measures in vegetables in the tropics. Estimated losses vary greatly among different crops. In carrots, losses can reach 100%, depending on factors such as population density, cultivar susceptibility, nematode species, soil class and environmental conditions, especially the combination of susceptible cultivars planted in soils with high population levels of the pathogen. However, even with low infestations, production can be compromised by up to 25%. Losses generally occur due to a reduction in the quantity and quality of the harvested product.
The most significant damage results from attack by root-knot nematodes, generally M. unexplained e M. javanica which have greater territorial distribution in different Brazilian regions, although other species such as M.hapla e M. arenaria are observed in isolated areas of the country. In carrot cultivation in Brazil, species of Meloidogyne most common are M. unexplained e M. javanica.
Several factors interfere with the reproduction and development of nematodes, such as temperature and soil humidity. Soil temperatures around 15ºC to 30°C are optimal for reproduction. They can become inactive between 5ºC and 15°C and between 30ºC and 40°C. Below or above these limits, temperatures can be lethal, depending on the exposure time. As for soil moisture, normally the optimum condition for the plant is the optimum for the nematode. Dry or water-saturated soils are always unfavorable for the survival of these nematodes. Thus, the main factors that affect the survival and movement of Meloidogyne in soil are soil temperature, humidity and aeration.
An important aspect of the life cycle of these pathogens is that the female can produce an average of 500 eggs to a thousand eggs, generally deposited on the surface of the roots, which can be seen with the naked eye. The nematode life cycle is 21 to 45 days, depending on environmental conditions.
Damage caused by root-knot nematodes (Meloidogyne spp.) are reflected in the aerial part of plants, with reduced development, yellowing and premature fall of leaves, unequal size of plants, with varying degrees of dwarfism, in addition to wilting in the hottest hours of the day, due to reduced absorption and translocation of water and nutrients by the host plant, resulting from reduced root volume and disorganized vascular system, due to the formation of galls.
Typical symptoms of the disease in areas with high infestation, as observed in the region of Alta Floresta, Mato Grosso, were the presence of galls on the roots (popularly known as “popcorn”), deformation, bifurcation and changes in the surface of the roots (becoming the rough ones), reduced development of the aerial part, yellowed leaves, reduced size and deformed roots due to the presence of galls. As the disease progresses, there is a reduction in the weight of the roots, plants with short carrots, often forked, which interferes with the classification commercial of the product.
The most efficient methods of controlling nematodes are genetic resistance and crop rotation. Considering that once introduced it is practically impossible to eliminate nematodes from the soil, and as carrots are an annual crop, the damage will be greater the higher the initial population levels in the soil. Therefore, control measures that reduce the initial population or reduce the infective capacity of nematodes should be prioritized:
It is important to remember that plants with symptoms of nematode incidence must be sent for analysis in a specialized laboratory, in order to diagnose and adopt appropriate control measures.
It is up to the producer and/or specialized professional to carry out prior research before installing the crop, to choose the cultivar that best adapts to the region and to be informed about the main pathogens occurring in the area. Remembering that seeds of several carrot cultivars are normally found on the market, with each cultivar having its own characteristics in terms of root shape, resistance to diseases and, mainly, in terms of planting time. When it comes to nematodes, consider that the most efficient control methods are genetic resistance and crop rotation. After all, the place for galls is not on the roots.
By Dilânia Lopes de Matos, Cleverson Rodrigues, Andre Lavezo, Alan Carlos Batistao, Ludilheia V. Bonfante, Grace Queiroz David, Paulo Sergio Koga e Walmor Moya Peres (Univ. of Est. of Mato Grosso)
Check out the article in issue 83 of Cultivar Vegetables and Fruits Magazine
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