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Colletotrichum spp. in Olive Growing

Francesc García-Figueres

Plant Health Laboratory. Department of Agriculture, Livestock, Fishing, Food and the Natural Environment. Government of Catalonia

Anthracnose is a fungal disease that severely affects olives and has a negative impact on oil quality. It is widely distributed in olive-growing regions around the world with greater or lesser intensity. It is found persistently in the districts of Baix Ebre and Montsià (Tarragona province, Catalonia), where early in the 1990s the oil produced was highly acid, over 15% oleic acid. In infected olives a delay in milling or the use of harvesting systems that may injure the fruit can contribute substantially to degradation of the oil.

Anthracnose is a fungal disease that severely affects olives and has a negative impact on oil quality. It is widely distributed in olive-growing regions around the world with greater or lesser intensity. It is found persistently in the districts of Baix Ebre and Montsià (Tarragona province, Catalonia), where early in the 1990s the oil produced was highly acid, over 15% oleic acid. In infected olives a delay in milling or the use of harvesting systems that may injure the fruit can contribute substantially to degradation of the oil.

The fungi related to this disease belong to the Colletotrichum genus (C. acutatum and C. gloeosporioides); the pathogen was called Gloeosporium olivarum when it was first described. C. acutatum is considered to be the majority species in the Baix Ebre and Montsià districts, where it is isolated in 80% of cases.

Olives infected with Colletotrichum may later be colonized by other fungi, which aggravates the quality issue. Cladosporium spp. is particularly relevant because it can lead to a considerable increase in peroxide levels (rancidification).

One of the most important aspects of the biology of this fungus is that the initial infection may occur during flowering, fruit set or hardening of the pit (to mention some of the important phenological stages). It may remain latent until conditions are favorable for fungal growth (when ripening begins), which can influence the control strategy. It is important to use strategies that minimize primary infections that occur when phenological and environmental conditions (such as temperature and humidity) are favorable.

In recent years technicians in the olive-tree Agrupacions de Defensa Vegetal (Plant Defense Groups) (ADV) fin Baix Ebre and Montsià have meticulously monitored the presence and degree of the disease in these districts, and various alternatives for disease control have been assessed and proposed. It was observed that control of primary infections can excessively escalate the cost of growing, and the focus is now on applying treatments when the fruit begins to change color. Using combinations of fungicides at this phenological period is acceptably effective, as long as the timing takes safety into account, to avoid residue.

Varietal sensitivity is an important aspect to look at in production areas around the world to assess the potential impact of this disease. Factors to be considered are the time of ripening (which involves specific climate conditions) and the physiological condition of the tree (nutritional balance, vigor, etc.).

It has been observed in the Baix Ebre and Montsià districts that the Morruda variety is the most sensitive under controlled conditions, followed by Sevillenca and Farga. The Sevillenca variety ripens early and the incidence is therefore usually higher, whereas the Morruda variety ripens later (December-January) and appears to be less sensitive because it escapes the climate conditions that favor the fungus. The incidence may actually be very high in years in which winter temperatures are milder.

The impact on the fruit is by far the greatest in terms of lost harvest and lower-quality oil, but the impact on other structures may also be of great concern. It has been noted that infection in the olives may cause branches to dry out, in part owing to mycotoxins that affect tender organs whether or not they harbor fungal structures. This fact was "ignored” for decades because of the difficulty in isolating Colletotrichum from this material.

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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.