New olive tree varieties step up to fight against anthracnose

Department of Agronomy of the University of Córdoba (DAUCO)
  • A study by researchers at the University of Córdoba identified the olive varieties most resistant to an epidemic capable of ruining a year’s harvest
  • Heavy rainfall episodes in 1996 and 1997 triggered the largest olive anthracnose epidemic recorded in recent decades in Spain
  • The resulting research provides with valuable guidelines for a a healthy agricultural product that is increasingly grown around the globe

 

Anthrachnose, a rain-triggered disease

Anthracnose, also known as canker, is a disease caused by the fungus species Colletotrichum acutatum. It is one of the most destructive olive diseases, affecting both the quality and the quantity of the harvest; oil obtained from damaged olives is highly acidic and therefore unfit for human consumption, giving rise to major economic losses for farmers.

Heavy rainfall during the fruit ripening period stimulates the dispersal of fungal spores, which infect the crop, causing fruit rot and branch dieback. Heavy rainfall episodes in Spain in the years 1996 and 1997 triggered the largest olive anthracnose epidemic recorded in the country in recent decades, but at the same time prompted more intensive research into this pathogen.

 

Finding resistant olive tree varieties

In order to limit the losses caused by extreme situations such as these, Dr. Antonio Trapero Casas, Professor of Agronomy at the University of Córdoba, carried out research aimed at classifying olive varieties in terms of their susceptibility to anthracnose. Using a previously-designed method, the susceptibility of a total of 384 cultivars from the World Olive Germplasm Bank in Córdoba were tested in the course of three severe anthracnose epidemics.

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Olive tree at the experimental agricultural fields of DAUCO.

The findings enabled each cultivar to be assigned to one of five categories: highly susceptible, susceptible, moderately susceptible, resistant and highly resistant. The representative varieties for each category were, respectively: Ocal, Lechín de Sevilla, Arbequina, Picual and Frantoio. The research showed that almost all Spanish cultivars can be classed as highly susceptible, susceptible or moderately susceptible. Although some Spanish varieties appear in the most resistant 10%, they are not widely grown.

Within Andalusia, the most susceptible variety (Ocal) is uncommon, and found  only to the south of Córdoba; Lechín de Sevilla,another susceptible cultivar, is grown mainly around Seville. However, another susceptible variety – Hojiblanca – is grown all over Andalusia, accounting for most of the olive groves in southern Córdoba and northern Málaga. The good news is that Picual, the most widely grown variety of all, especially in Jaén, is remarkable for its resistance to anthracnose.

The health benefits associated with olive oil have prompted a spread of olive farming to countries where it was not hitherto a traditional crop, such as Australia, China and America. The severe economic losses suffered by newly-planted olive-groves all over the world are largely due to the wrong choice of variety, which can give rise to major anthracnose epidemics. With this new knowledge, farmers can now be sure of choosing the best anthracnose-resistant varieties when planting a new olive grove.

 

Image credit:

Olive tree kindly provided by DAUCO, and reused with permission.

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