The olive tree (Olea europaea L.) is among the oldest plants cultivated by man, having ecological, economic and even cultural importance in different countries. It is characterized by rusticity, not requiring very fertile soils or special water regime for its development, but with low tolerance to waterlogged soils and intense winters. Its cultivation is mainly concentrated in countries with a Mediterranean climate, represented by 95% of world production, of which 73% comes from countries belonging to the European Union. Spain is considered the largest producer of olive oil and olives, with 43% of world production, followed by Italy (18%) and Greece (12%). However, countries in South America, such as Chile and Argentina, have been excelling in this cultivation, currently reaching 1% of world production. Brazil is still a country dependent on fruit imports, and considered the second largest importer of olives in the world.
Currently, the increase in import volume, together with the growing number of research carried out on this crop, has encouraged farmers to invest in this crop in Brazil, mainly in the South (Paraná, Santa Catarina and Rio Grande do Sul) and Southeast ( Minas Gerais, Rio de Janeiro and São Paulo). However, despite the rusticity of the plant and the research carried out since its implementation, information on the cultural management of the olive tree in Brazil is still insufficient to clarify unknown questions for producers and researchers in the sector. It is worth highlighting the fact that olive cultivation can be affected by numerous pathogens, including plant parasitic nematodes, which can cause damage to the roots, affecting their development, or just live in the rhizosphere without causing damage.
In analyzing the available international literature, it is possible to find records of 153 species belonging to 56 genera of phytoparasitic nematodes associated with the rhizosphere of olive trees. Some of these species can cause losses to olive plants, such as Xiphinema index, X. elongatum, Pratylenchus vulnus, P. penetrans, Meloidogyne arenaria, M. javanica, M. incognita, Tylenchulus semipenetrans e Rotylenchulus macrodoratus. However, Pratylenchus (nematode that causes necrotic lesions on the roots) and Meloidogyne (root gall nematode) are the genera that have been causing the most damage, especially to seedlings in nurseries. In Brazil, Meloidogyne spp. And Pratylenchus ssp. They are the most widespread nematodes and responsible for significant economic damage to annual and perennial crops.
The main symptoms observed in plants parasitized with Meloidogyne ssp. are the reduction in shoots in olive cultivars, the presence of galls on the roots and consequently the reduction of the root system. Olive trees infected by Meloidogyne spp. they also present yellowing of the upper leaves, followed by defoliation, similar to nutritional deficiencies. Olive trees infected with Pratylenchus ssp. present similar symptoms, but instead of galls, darkened lesions (necrosis) are observed on the roots. Furthermore, the mechanical action caused mainly by the nematode stylet favors the entry of secondary pathogens such as Verticillium dahliae, causing wilting and further aggravating the damage. For example, there is the association of M. unexplained e P. vulnus with the fungus V. dahliae.
In Brazil, studies on the occurrence and damage caused by these organisms are limited to reporting the occurrence of M. javanica in olive trees in Rio Grande do Sul in 1974 and the presence of M. unexplained race 1 and Helicotylenchus dihystera in the area of the seedling and matrix production nucleus of the Integral Technical Assistance Coordination (Cati), located in São Bento do Sapucaí, São Paulo, in 2005. Despite being a new report of M. unexplained race 1, this species was detected at a low population level, with no symptoms of decline observed in plants cultivated at the site.
With the growth of olive tree cultivation in the state of São Paulo, a multidisciplinary group was formed with researchers linked to the Department of Agriculture and Supply of the State of São Paulo, such as APTA – Polo Centro Sul, Instituto Agronomic (IAC), of Food Technology (Ital) and the Instituto Biológico (IB), which developed the project called Oliva SP (http://www.apta.sp.gov.br/olivasp), aimed at studying the stages of the crop production chain (phytotechnics), including the phytosanitary aspects of olive cultivation.
One of the objectives of the Oliva SP group was to promote the survey of phytoparasitic nematode species associated with olive cultivation in 14 municipalities in the state of São Paulo: Bom Sucesso do Itararé, Cabreúva, Cunha, Ibiúna, Itatiba, Lindoia, Pedra Bela, Piedade, Pindamonhangaba, Pilar do Sul, Santo Antônio do Pinhal, São Bento do Sapucaí, São Pedro and Serra Negra. In these locations, nematological samples were collected, nematodes were extracted from 250cm3 of soil and 10g of roots, and identification was carried out using light microscopy with the aid of other techniques (isoenzyme/esterase electrophoresis and PCR), in the nematology laboratory of the Biological Institute, in Campinas, São Paulo.
Based on this survey, 11 species of nematodes were identified (Figure 1), observing the prevalence of Helicotylenchus dihystera, present in 88% of the collected samples, followed by Pratylenchus brachyurus, present in 53% of the samples. Some identified species constituted new occurrences for olive trees in Brazil: H. erithrinae, P. brachyurus, P. zeae, Xiphinema diffusum, X. krugi, X. surinamese e X. variegatum. In addition to these species, X. santos was identified by morphometric, morphological and molecular analysis in the municipality of Bom Sucesso de Itararé, São Paulo, being the first occurrence of this species in association with olive trees in the Southern Hemisphere and outside the European and African continents, expanding its geographic scope.
It is worth noting that some olive cultivars showed characteristic symptoms, such as the species M. javanica which caused well-defined galls on the roots of cultivars Arbequina and Koroneiki, and P. brachyurus which caused marked necrotic lesions on the roots of the cultivars Arbequina, Arbosana, Koroneiki and Maria da Fé, harming the development of some plants.
Another factor observed in Brazilian olive groves that deserves attention is the intercropping of olive tree cultivation with annual plants between rows or borders. For example, plants of the Arbequina and Arbosana cultivars showed symptoms of reduced development with necrotic roots, stand failure and a high number of P. brachyurus, probably due to the increase in the local population due to the situation of intercropping with beans, corn and brachiaria, plants considered hosts of this species. In another area, the cultivars Arbequina, Grapollo, Koroneiki and Maria da Fé grown among brachiaria had a high population level of P. brachyurus, causing problems in plant development. It was also possible to observe plants such as pumpkin, sweet potato and okra highly infested with Meloidogyne spp. on the edge of olive groves, increasing the population level of this nematode in the area, which could lead to the worsening of this problem in the future.
It is undeniable that, among the available measures to control phytonematodes, those of a preventive nature are more efficient and economical when compared to curative treatments. Preventive control's main strategies are the use of nematode-free seedlings and planting in non-infested areas, the information from which is obtained through prior nematological analysis of the soil and roots of the crop before it is established in the area to be cultivated.
As highlighted in many publications on nematodes in different perennial crops, the main way of introducing phytonematodes into cultivated areas is through contaminated seedlings. Therefore, the use of certified seedlings is crucial to prevent the introduction and spread, as highlighted by Professor Ailton Rocha Monteiro (Esalq-USP), in 1981: “Nematodes should not be planted”. In the case of irrigated crops, avoid using contaminated water. The handling of agricultural implements and machinery deserves special attention, especially when used in infested areas. They must be properly disinfested before being used in other unharmed planting areas. Therefore, the movement of machines and people from infested to healthy areas must be constantly monitored.
Information on nematode-resistant olive cultivars is still very scarce. However, European and national studies demonstrated that some cultivars behaved as resistant to species of Meloidogyne. Table 1 lists the olive tree cultivars with this resistance.
chemical control
There is no record at the Ministry of Agriculture, Livestock and Supply (Mapa) of nematicides in olive cultivation.
The increase in organic material, in addition to improving the physical-chemical relationships of the soil, favors plant growth, making them more tolerant to nematode attacks. It also promotes the growth of populations of natural enemies of nematodes. Furthermore, the decomposition of organic matter releases compounds that are highly toxic to phytonematodes.
Weed management is essential, preventing root-knot or lesion nematodes from surviving or multiplying in these plants.
The use of soil solarization techniques has also been effective for disinfestation against nematodes in seedling nurseries.
Laboratory analysis is essential for diagnosing the presence and identification of phytonematodes in the area. Collecting a sample for analysis and choosing a good laboratory are essential for managing the area.
Considering that the main nematodes parasitize olive roots, common sense must prevail when collecting and sending nematological samples. The ideal is to collect the sample in the projection of the olive tree canopy. The soil must be opened with the help of a hoe to a depth of 20cm to 30cm, collecting soil and mainly finer roots. Therefore, at least ten subsamples per hectare must be collected, totaling a sample consisting of approximately 1kg of soil (with natural humidity) and 50g of roots.
Preferably, the roots should be placed in the soil mixture to prevent them from drying out. Samples (soil + roots) must be packed in resistant plastic bags and sent quickly for analysis. Samples must be correctly identified with the following information: place and date of collection, name of the plant (cultivar), property and owner, address to send the results and contact telephone number. The Biological Institute is capable of receiving samples and identifying nematodes - http://www.biologico.sp.gov.br/page/produtos-e-servicos/exames/exames---area-de-sanidade- vegetable.
Juliana Magrinelli Osório Rosa, Claudio Marcelo Gonçalves de Oliveira, Biological Institute, Advanced Research Center for Plant Protection and Animal Health, Nematology Laboratory
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