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Management of Tylenchulus semipenetrans in citrus orchards

Soledad Verdejo-Lucas and F. Javier Sorribas

IFAPA. Camino de San Nicolás 1. 04745 La Mojonera. Almeria. España. Soledad.verdejo@juntadeandalucia.es | ESAB. Universidad Politécnica de Cataluña. francesc.xavier.sorribas@upc.edu

The citrus nematode is the most widespread plant-parasite associated to citrus worldwide. The estimated yield losses are in the range of 10% to 30% depending on the level of infection. Nematode management implies the concerted use of various tactics through the life-span of the orchard. Exclusion and preventing measures include regulatory activities, use of certified nematode-free rootstocks, nematode-free soil or growth media and sanitation.

The citrus nematode is the most widespread plant-parasite associated to citrus worldwide. The estimated yield losses are in the range of 10% to 30% depending on the level of infection. Nematode management implies the concerted use of various tactics through the life-span of the orchard. Exclusion and preventing measures include regulatory activities, use of certified nematode-free rootstocks, nematode-free soil or growth media and sanitation. Once nematodes are detected within a production region, the most effective strategy is to reduce initial population densities prior to establishing an orchard. Physical disturbance and soil manipulation can accelerate the mortality rate of nematodes due to desiccation or direct exposure to sunlight although nematodes may survive within remnant citrus roots or deeper in the subsoil for long periods of time. Pre-plant soil disinfestation by chemical fumigation is the most effective way to control nematodes and should be considered when replanting citrus orchards. Poncirus trifoliata is the only source of genetic resistance against T. semipenetrans and some of the resulting hybrids with Citrus greatly inhibit nematode reproduction in comparison to susceptible rootstocks. A progressive adaptation of the nematode to reproduce on rootstocks with moderate resistance (i.e. Carrizo citranges) can occur due to their continuous cultivation. In addition, the existence of physiological races or biotypes of T. semipenetrans that differ in their host preference poses a limitation to rootstock selection. Once trees are infected, no curative methods of nematode control are available. The life cycle of T. semipenetrans is regulated by host phenology and seasonal changes in the soil, a fact to be considered for the use of post-plant control tactics. The number of females infecting roots is the best indicator of seasonal activity of T. semipenetrans and also for evaluating the efficacy of nematicides. Non-fumigant nematicides (oxime-carbamates and organophosphates) have successfully been used to decrease densities of T. semipenetrnas on citrus in many regions. However, repeated applications are needed to maintain reduced densities and consistent yield increases. A diversity of microbial antagonists occurs naturally in citrus and they can regulate nematode populations through direct parasitism or predation in a density dependent manner or via release of toxic metabolites. However, it remains an experimental system, and additional field data are needed to increase the knowledge on the nematode- antagonist relationship once applied in the field. Regarding to agronomic and cultural practices, rotations with annual crops for 1 to 3 years before replanting citrus helps to reduce nematode populations but the economics of such rotations limits their use. Fallowing for 4 months to 1 year before replanting an orchard is a common practice but may not be sufficient due to nematode survival within old roots. Mulching is a cultural practice that can help reduce water loss from the soil as it reduces evaporation, moderates extreme daily soil temperatures, and helps suppress weed competition. As a consequence, the crop’s environment is modified, promoting tree vigor and increased yield. Nematode densities may increase on mulched trees, but those trees may be more tolerant to nematode damage because of reduced temperature and moisture stresses. In summary, management of T. semipenetrans requires a thorough understanding of the growth of the host plant, the biology, ecology and epidemiology of the nematode, and the influence of the environment on the nematode-plant interaction in a given region.

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PRODECA guarantees that you may, at any time, exercise your right to access, rectify, cancel or oppose by writing to the aforesaid postal address, using the reference "PROTECCIÓN DE DATOS - SMARTFRUIT", or to the email address smartfruitcongress@smartfruitcongress.cat.

Specifically, to correctly exercise these rights you must clearly provide the following items in that communication:
- Name, surname(s) and photocopy of National Identity Document or Passport.
- Statement of the purpose of the request.
- Address for notification purposes.
PRODECA also declares that it reserves the right to delete from its website any content that it considers violates current and applicable legislation.

D’acord amb l’article 17.1 de la Llei 19/2014, la ©Generalitat de Catalunya permet la reutilització dels continguts i de les dades sempre que se'n citi la font i la data d'actualització i que no es desnaturalitzi la informació (article 8 de la Llei 37/2007) i també que no es contradigui amb una llicència específica.