How a tiny leafhopper from Algeria threatens Morocco's farms

Researchers have recently sounded the alarm regarding a pressing threat to Moroccan agriculture with the presence of the Graphocephala versuta (hereafter G. versuta) insect in Algeria. 

This small insect, notorious for transmitting the destructive Xylella fastidiosa (X.f) bacterium, poses a serious risk to a diverse range of plants. If introduced, the potential spread of this bacterium could spell disaster for Moroccan agriculture.

The bacterium attacks more than 350 species, including cultivated plants, wild plants, and forest species. It induces many plant diseases causing yield losses and plant death of many economically important crops, like grapevine, peach, plum, almond, citrus, olive trees, forest system, and oleander.

Imagine X.f as a sneaky troublemaker slipping into a plant’s vascular system, known as the xylem. This system acts like the plant’s water highway, transporting the water and nutrients it needs to grow. 

But once X.f gets in there, it clogs up the works, blocking the water supply and essential nutrients from reaching where they’re needed.

This blockage leads to significant problems, with the plant struggling to draw water from its roots to its leaves, resulting in wilting, especially during hot weather. 

With the flow disrupted, the plant becomes malnourished, further hindering its growth and development.

The signs of this internal struggle become visible on the leaves. They often develop scorching at the edges, turning brown or yellow, as the lack of water and nutrients takes its toll. This scorching can spread inward as the condition worsens, leaving the leaves looking withered and unhealthy.

Among the devastating diseases associated with this bacterium, you can find:

•  Olive Quick Decline Syndrome (OQDS), which leads to rapid decline and death of olive trees; Once the bacterium infects a plant there is no treatment other than to remove infected limbs or whole trees to try and prevent the spread.
• Citrus Variegated Chlorosis (CVC), causing yellowing of leaves and reduced fruit quality in citrus trees; 
• Pierce’s Disease (PD), resulting in wilting and eventual death of grapevines; 
• Almond Leaf Scorch Disease (ALSD), manifesting as leaf scorching and decline in almond tree health; and 
• Oleander Leaf Scorch Disease (OLSD), causes leaf yellowing, browning, and eventual death of oleander plants.

Despite the abundant presence of suitable insect carriers, such as Psylla tesselatus, which could potentially serve as vectors if the bacterium introduced, Morocco has managed to remain free of the X.f as of 2022.

However, the situation is of course not without concern. With G. versuta, a potentially problematic carrier, existing in neighboring Algeria, the threat to Moroccan agriculture looms large from across the border, according to recent research.

A study conducted between 2013 and 2014 near Reghaia Lake, Algeria, which is surrounded by vineyards, olive orchards, citrus orchards, and fruit trees orchards, examined insect diversity. Three insects initially and incorrectly identified as G. fennahi were captured in October 2013 but were later confirmed by an expert to be G. versuta, the insect vector for the devastating X.f.

On August 3, 2019, the same species was discovered in a vineyard in Skikda region, Algeria, approximately 350 km from the initial location. This marked the first observation of G. versuta, which belongs to the family Cicadellidae, commonly known as leafhoppers, in Africa and the Palearctic region.

In Morocco, none of the cicadellid genera reported worldwide as vectors of X.f have been identified, according to research.

However, as for the bacterium itself,  it has been classified as a quarantine pest in Morocco under Ministerial Order No. 832-02 of June 12, 2002, regulating the importation of plants or plant parts that could be infested by certain harmful pests. 

Yet, findings from an article investigating the potential spread of harmful plant bacteria across Europe, the Middle East, and North Africa revealed that Morocco faces a significant risk from this disease. 

This is because Morocco imports plants from regions already battling X.f, like Europe, including stone fruit trees, olive trees, ornamental plants, grapevines, and more, making it easy for the disease to enter the country. Besides, asymptomatic plants or those with latent infections pose a risk.

What is more, Morocco’s climate and crop types are particularly susceptible to X.f, increasing the risk of the disease establishing itself and causing harm.

There is also intense movement of people and vehicles between Morocco and European countries, including those that are contaminated. 

For this reason, national phytosanitary regulations mandate special measures, including prohibiting its introduction, requiring the declaration of any suspected presence, and enforcing control and eradication if detected.

To prevent the introduction of the bacterium in Morocco, ONSSA has implemented a range of measures, including systematic inspections of all plants arriving from abroad. The office has also established a program for monitoring and surveillance, along with sampling and diagnostic facilities. 

Also, ONSSA, in coordination with Interprolive, organizes training sessions for farmers to raise awareness.