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Diseases caused by Phytophthora and Alternaria in citrus crops

José García Jiménez

Instituto Agroforestal Mediterráneo. Universidad Politécnica de Valencia

The oomycete Phytophthora spp. and the true fungus Alternaria alternata are two ofthe main causal agents of fungal-associated diseases in citrus crops in Spain. 

Several species of Phytophthora, including P. citrophthora, cause a complex syndrome that can affect almost all citrus species and varieties, which is characterized by the development of damage to the roots (loss of rootlets and canker formation in thick roots), trunk and branches (necrosis and exudation of sap; "gumming"), and the browning and rotting of fruit.

The oomycete Phytophthora spp. and the true fungus Alternaria alternata are two ofthe main causal agents of fungal-associated diseases in citrus crops in Spain. 

Several species of Phytophthora, including P. citrophthora, cause a complex syndrome that can affect almost all citrus species and varieties, which is characterized by the development of damage to the roots (loss of rootlets and canker formation in thick roots), trunk and branches (necrosis and exudation of sap; "gumming"), and the browning and rotting of fruit. The disease is particularly severe in heavy clay soils prone to waterlogging and fruit damage can be exacerbated by heavy rain. Control  measures include the use of resistant rootstocks and the implementation of specific cultural practices (improved drainage, drip irrigation, planting in raised beds, leaving a no-sod circle around the tree base, blanket irrigation, use of cover crops, etc.), as well as chemical treatment, applied mainly in spring and autumn. 
The pathotype of Alternaria alternata that causes brown spot has a much smaller host range (affecting mainly the "Fortune" and "Nova" cultivars in Spain), but causes such severe damage that it has drastically reduced the land area under Fortune cultivation. The toxin ACT, which is produced during spore germination, rapidly causes lesions on the leaves (resulting in severe defoliation), shoots and fruits, producing lesions in the cortex that completely devalue the fruit. In the Fortune cultivar, the leaves are only susceptible when young, whereas the fruit is susceptible at all stages of development. 
Development of this disease requires a rainfall event of at least 10-12 hours in duration, and an optimum temperature of 25-27°C. It is recommended not to plant susceptible varieties in humid and poorly ventilated areas, to improve aeration (removal of some main branches, planting in widely spaced rows, oriented in the direction of the prevailing winds), to reduce sources of inoculum by removing affected plant material, and to remove suckers, which are highly susceptible to attack. It is also necessary to administer chemical treatments using mancozeb or copper products, which are the only products authorized in Spain for the effective treatment of this disease. As symptoms develop rapidly after infection, treatments should be applied preventively when conditions that favor infection are forecast.

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Data protection policy

In accordance with the Organic Law on the Protection of Personal Data 15/1999, of 13 December, Promotora de Exportaciones Catalanas SA (hereinafter PRODECA), whose address is Gran Via de les Corts Catalanes, 620, principal, 08007 Barcelona, with tax reg. no. NIF A58241316, declares that the images contained on the website www.smartfruitcongress.cat are included in a file belonging to PRODECA. The purpose of this file is the promotion, via its website, of the activities conducted by PRODECA – SmartfFruit IPM International Congress.

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.