The Essence of the Olive: Xylella fastidiosa and Olive Quick Decline Syndrome (OQDS)

Across the Mediterranean, Xylella fastidiosa has become one of the most destructive plant pathogens in modern European agricultural history, reshaping entire landscapes and threatening a cultural legacy built on thousands of years of olive cultivation. What began as an isolated detection in southern Italy has evolved into a regional crisis, with the bacterium spreading through parts of Spain, France, and beyond. Its impact is profound: ancient groves are dying, rural economies are destabilizing, and the ecological balance of traditional olive‑growing regions is under unprecedented strain. The most widely supported hypothesis is that Xylella fastidiosa entered Italy on an imported coffee plant from Costa Rica sometime in 2008.

At the heart of the devastation is the way Xylella fastidiosa attacks the olive tree. The bacterium colonizes the xylem—the vessels responsible for transporting water and nutrients—gradually clogging them until the tree can no longer sustain itself. The result is Olive Quick Decline Syndrome (OQDS), a condition marked by leaf scorch, branch dieback, and the rapid collapse of the entire canopy. Once symptoms appear, the decline is often irreversible. The disease spreads primarily through sap‑feeding insects, especially the meadow spittlebug, which thrives in Mediterranean climates and can move easily between wild vegetation and cultivated groves. 

The outbreak in Puglia, Italy, remains the most dramatic example of the pathogen’s destructive potential. Since its detection in 2013, millions of trees—some more than a thousand years old—have died. Entire landscapes once defined by silvery olive canopies now stand barren, their skeletal remains a stark reminder of how quickly the disease can transform a region. The emotional toll on farming families, many of whom have tended the same groves for generations, is as significant as the economic loss. Olive oil production in affected zones has plummeted, and the region’s iconic agrarian identity has been deeply shaken.

Spain, the world’s largest olive oil producer, has also faced serious challenges. The Balearic Islands and parts of mainland Spain have recorded multiple subspecies of Xylella, some of which infect not only olives but also almonds, grapes, and ornamental plants. The diversity of host species makes containment especially difficult. Unlike Puglia’s relatively concentrated outbreak, Spain’s cases are more dispersed, complicating eradication efforts and raising concerns about long‑term persistence.

Governments and researchers have mobilized aggressively, though progress is slow. Traditional farming practices—such as maintaining grassy understory vegetation—can inadvertently support spittlebug breeding, forcing growers to rethink long‑standing land‑management habits. Containment zones, mandatory tree removal, and restrictions on plant movement remain central strategies, but they are controversial and emotionally painful for affected communities. On the scientific front, hope lies in tolerant olive cultivars such as Leccino and FS‑17, which show resilience against the bacterium and are now being planted widely in Puglia. Researchers are also exploring biological controls, improved vector management, and advanced diagnostic tools to detect infections earlier.

Still, the path forward is complex. Xylella fastidiosa is notoriously difficult to eradicate once established, and the Mediterranean’s interconnected agricultural systems make long‑term vigilance essential. The crisis has become a defining test of how Europe responds to emerging plant diseases in an era of globalized trade and climate instability.

What remains clear is that the Mediterranean’s olive heritage—its landscapes, its economies, its cultural identity—faces a generational challenge. Yet amid the devastation, there is resilience: farmers replanting with tolerant varieties, scientists pushing the boundaries of plant pathology, and communities rallying to protect a symbol that has defined their region for millennia.

The Essence of the Olive: The World of Olive Trees

 🌿 When we think of olive oil, we often picture sun-drenched groves, silvery leaves rustling in the wind, and ripe fruit ready for harvest. But behind every bottle lies a key factor that shapes flavor and identity — the olive variety, or cultivar. Much like grape varieties in wine, each olive tree expresses its own personality through aroma, texture, and taste, influenced by soil, climate, and the hands that tend it.

Across the Mediterranean and beyond, there are over 1,000 known olive cultivars, each adapted to its region’s terrain and traditions. Let’s explore some of the most influential varieties — the ones that define the world’s great olive oils and reveal the diversity of this ancient tree.

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Italy: Bold and Diverse

Italy boasts more olive cultivars than any other country, and each region offers a unique expression.

• Frantoio – The star of Tuscany. Frantoio oils are aromatic and complex, with notes of green herbs, artichoke, and a peppery finish. Often blended with Leccino for balance.
  
  

• Leccino – Milder and softer than Frantoio, producing round, buttery oils with hints of almond and apple. Common in central Italy.
  
  

• Coratina – The pride of Puglia, this variety yields intensely green, spicy, and bitter oils with exceptional shelf life — a favorite among chefs for its structure.
  
  

• Nocellara del Belice – From Sicily, known for dual-purpose use (table olives and oil). Fruity, balanced, and slightly nutty, it captures the island’s warmth in every drop.
  

Italian cultivars are often blended, much like wine cuvées, to achieve harmony between fruitiness, bitterness, and pungency.

The Essence of the Olive: Introducing Our Olive Oil Series

Few ingredients in the world of food carry as much heritage, versatility, and symbolism as olive oil. For thousands of years, this golden liquid has nourished civilizations, inspired poets, and defined entire culinary traditions. From the rocky hills of Greece to the sun-drenched groves of Spain, from the ancient presses of Italy to the emerging producers of California and beyond, olive oil remains a cornerstone of culture, craft, and cuisine.

In this new series, we’ll explore olive oil from root to bottle — uncovering the stories, science, and people behind it. We’ll delve into how geography and climate shape its character, how different olive varieties yield distinctive aromas and flavors, and how modern producers balance innovation with ancient methods. You’ll learn what makes an extra virgin truly “extra,” how to taste olive oil like a professional, and how to pair it with food and wine.

Join us on this journey through groves, mills, and markets as we uncover the world of olive oil — one harvest, one taste, one or two stories at a time.

So let's jump in. What is Extra Virgin Olive Oil (EVOO)? 

Extra virgin olive oil is the highest quality grade of olive oil, made exclusively from the first cold-pressing of olives without heat or chemicals, resulting in a superior flavor, aroma, and higher nutritional value. The cold-pressing retains more antioxidants, polyphenols, and vitamin E, contributing to its anti-inflammatory properties and health benefits. Finally, the olive oil must have a free acidity level of 0.8% or less and is assessed by a tasting panel to ensure it has no defects and a distinct fruity character. 

In contrast, virgin olive oil has a higher acidity level (between 0.8% and 2.0%) and may have minor defects detectable by taste, making it less flavorful and less nutritious than EVOO.  Virgin olive oil is often produced by blending refined olive oil with a small amount of virgin or extra virgin oil to improve its taste and color, which reduces its health benefits compared to EVOO. Since virgin olive oil is typically lighter in color, milder in flavor, and less expensive than extra virgin olive oil it is more suitable for cooking at higher temperatures where its flavor is less critical.

The production of EVOO requires olives to be harvested at optimal ripeness and processed quickly (often within 90 minutes) to preserve quality, while virgin olive oil can be made from olives with higher acidity or from later harvests.  The production process will be covered more in depth next week with From Tree to Taste: How Olive Oil Is Made.

Fattoria Poggio Alloro is an agritourism destination providing spectacular views of San Gimignano and the surrounding rolling hills. The farm is located 40km southwest from Florence and only 5km from San Gimignano.  The name Poggio Alloro means Bay Leaf Hill, and it refers to the bay laurel bushes that grow everywhere on their property. There's a multitude of agricultural commodities grown on the one hundred hectares from grapes; fruits; vegetables; and grains: barley, oats, corn, sunflowers, durum, wheat, farro; and olives.

More specifically 1,500 olive trees that are used in the production of extra-virgin olive oil. The Leccino, Moraiolo, and Frantoio varieties are completely hand picked in November, and then cold pressed to guarantee superior quality.   Their EVOO has a golden yellow color with light green tones and has a stone fruit, slightly spicy flavor with an intense finish.