10 – Plant Disease and Insects

Just like you, plants also get ill due to bacteria, viruses and fungus that something may result in death. This week's weblog will look into the different bacterial, viral and fungal diseases, the possible treatments that can be used to cure the infected olive tree.

Deadly and sickening insects and diseases

Xylella fastidiosa is a bacteria that is carried by the meadow spittle-bug, which have been making the life of Italian farmers very difficult in growing “healthy” olive trees. This is because the insect contains a bacterium that has resulted in thousand groves being destroyed (Latza, 2016) (Neslen, 2015). This pathogenic bacteria is said to cause Olive Quick Decline Syndrome (OQDS), resulting in the tree to wither and desiccation of terminal shoots, expanding to the rest of the canopy which causes the tree to collapse and eventually die (G. Loconsole, 2014) (Borkhataria, 2017). It all start when a tree is injured, an open wound where the bacteria can enter the plant. Once the xylella fastidiosa has invaded and multiplied within the plant’s xylem vessels, it blocks the vessels making it difficult for the tree to transport water and nutrients from its roots to the shoots and leaves. Ever since the outbreak in 2013 little research had been carried out regarding the bacteria and for years nobody knew what to do against it (PHYS.ORG, 2017) (The Local, 2017). However, now insights suggest that growers could “control” the disease by extensively pruning the trees, instead of clear-cutting all the (infected) plant.

Interestingly, is that special consideration is granted to the region’s famous 100 year old secular trees and 1,000 year old millennial trees. This is because these trees are considered as official national landmarks (Latza, Italy's Olive Trees Didn't Have to Die, 2016). However, Europe have order Italians to cut down all infected olive trees (Squires, 2016).

Within the EU the bacteria is regulated as quarantine organism under Council Directive 2000/29/EC (Plant health Directive) (European Commission, 2017). This regulation provides member states with legal obligation abide that once the organism is know to be present. So should the buffer zone be of a width of at least 10 km, which surrounds the infected zone. Moreover, “strict eradication measures should not only apply in the infected zone, but also in any buffer zone, where new findings occur”.

Figure 1: Map of Xylella fastidiosa bacteria worldwide (Latza, 2016)

The orange coloured countries is where the bacterium is present, while countries in purple is where the bacteria is transient.

Figure 2: Examples of Agrobacterium tumefaciens trees (Denesia, 2015)

The bacterium Agrobacterium tumefaciens mainly affects the younger olive trees, whereby lumps, gall or tumors grow on the part where the stem branches from the roots (Sabor-Artesano, N.D.). Once the bacteria has invended the tree it prevents correct circulation of the sap, resulting in the tree to die (usually takes two or three years). The existing treatments are said to not be effective. Therefore one is adviced to keep its tree from any injuries, since the bacteria enters a crop through cuts or/and exposure to air.

Viral, Bacterial and fungal diseases

Bacterial:

The most well-known bacterial disease that attack olive is Xylella fastidiosa, which has already been covered above.

Fungal:

The fungus Deuteromycetes, causes fruit rot or as it is also known Olive Anthracnose (Olive soap) (Sabor-Artesano, N.D.). The disease acts against the olive and is said to attack the leaves, buds and woods. It is especially in humid areas how it develops, especially in the southern and north-eastern of Spain. Moreover, the disease affects the quality of olive oil and farmers are said to lose 40% of their crop. Once the tree is affected the following symptoms occur:

• ·         Foam coming out of the olive because of the rotting within the tree.

• ·         Drying out of branches which results in the leaves to dry and wither.

Treatments: One recommends to use products that contains copper and to immediately act when damage occur.

Viral:

The virus Olive latent virus 2 (OLV-2) is said to occur symptomless in Olea species, and one of the several mechanically transmissible viruses that infects olives trees in the southern of Italy (F. GRIECO, 1992) (A. Hadidi, 2011). However, the same virus did show symptoms in castor beans, which were yellowish vein netting and systematic mottling on leaves.

Treatment: Little could be found about the treatment, except that the tree are isolated to prevent further contamination (Castellano, 1991).

References

A. Hadidi, M. B. (2011). Viruses, phytoplasmas and diseases of unknown etiology of olive trees. ResearchGate. Retrieved December 06, 2017, from https://www.researchgate.net/publication/241687505_Viruses_phytoplasmas_and_diseases_of_unknown_etiology_of_olive_trees

Borkhataria, C. (2017, June 07). The American bug ravaging Italy's olive oil industry: Bacteria causes trees to wither and die - and there's no cure. Retrieved December 05, 2017, from Daily Mail: http://www.dailymail.co.uk/sciencetech/article-4581856/Italy-s-olive-trees-infected-bacterium-Xylella.html

Castellano, M. (1991). Olive latent 2 (?) ourmiavirus. Retrieved December 07, 2017, from Microbial Information Network of China: http://sdb.im.ac.cn/vide/descr536.htm

Denesia, M. (2015, April 06). 17 agrobacterium tumefaciens. Retrieved December 06, 2017, from SlideShare: https://www.slideshare.net/MerlynH/17-agrobacterium-tumefaciens

European Commission. (2017, December 06). Xylella fastidiosa. Retrieved December 06, 2017, from European Commission: https://ec.europa.eu/food/plant/plant_health_biosecurity/legislation/emergency_measures/xylella-fastidiosa_en

F. GRIECO, G. M. (1992). PROPERTIES OF OLIVE LATENT VIRUS 2. Società Italiana di Patologia Vegetale (SIPaV), 125-136. Retrieved December 06, 2017, from https://www.jstor.org/stable/42555733

G. Loconsole, O. P. (2014). DETECTION OF XYLELLA FASTIDIOSA IN OLIVE TREES BY MOLECULAR AND SEROLOGICAL METHODS. Journal of Plant Pathology. Retrieved December 05, 2017, from http://www.sipav.org/main/jpp/index.php/jpp/article/view/3096

Latza, B. (2016, April 05). Italy's Olive Trees Didn't Have to Die. Retrieved December 05, 2017, from Scientific American: https://www.scientificamerican.com/article/italy-s-olive-trees-didn-t-have-to-die/

Latza, B. (2016, April 05). Italy's Olive Trees Didn't Have to Die. Retrieved December 06, 2017, from Scientific Amaerican: https://www.scientificamerican.com/article/italy-s-olive-trees-didn-t-have-to-die/

Neslen, A. (2015, January 08). Europe’s olive trees threatened by spread of deadly bacteria. Retrieved December 06, 2017, from The Guardian: https://www.theguardian.com/environment/2015/jan/08/europes-olive-trees-threatened-spread-deadly-bacteria

PHYS.ORG. (2017, July 06). Spain hit by deadly bacteria threatening olive trees. Retrieved December 06, 2017, from PHYS.ORG: https://phys.org/news/2017-07-spain-deadly-bacteria-threatening-olive.html

Sabor-Artesano. (N.D.). OLIVE TREE DISEASES. Retrieved December 06, 2017, from Sabor-Artesano: http://www.sabor-artesano.com/gb/olive-tree-diseases.htm

Squires, N. (2016, June 09). Europe orders Italians to cut down olive trees infected with bacteria. Retrieved December 07, 2017, from Telegraph: http://www.telegraph.co.uk/news/2016/06/09/europe-orders-italians-to-cut-down-olive-trees-infected-with-bac/

The Local. (2017, February 04). Spain's Balearic Islands hit by deadly olive tree bacteria. Retrieved December 06, 2017, from The Local: https://www.thelocal.es/20170204/spains-balearic-islands-hit-by-deadly-olive-tree-bacteria