In the far south of Italy, Apulia is known for its beautiful coastline, the beauty of its landscapes, and an extraordinary historical, cultural, and gastronomic heritage. But the region may soon become famous for having found effective strategies in the fight against a bacterium that threatens the entire Mediterranean: xylella fastidiosa, the “olive tree plague.”
If Italy is one of the main producers of olive oil in the European Union, it is largely thanks to Apulia, with its 60 million olive trees. For years, however, this region has been facing the spread of an enemy as invisible as it is relentless to the olive tree: xylella fastidiosa. Giovanni Melcarne, owner of the agricultural company Forestaforte, in the province of Lecce (southern Apulia), specializing in the production of high-quality extra virgin olive oil, even remembers the exact day when it all began. “It was October 15, 2013. The official announcement confirming the presence of xylella fastidiosa on the olive trees in Apulia was made.” Since then, this bacterium has destroyed more than 21 million olive trees. Among them, many trees known simply as the “centenarians,” aged hundreds, sometimes even thousands of years, with trunks that can reach ten meters in circumference.
The “olive tree plague”
Walking among such ancient trees is a unique experience. Among the most cherished places by locals and tourists is the famous Plain of Monumental Olive Trees: a rural area between the cities of Bari and Brindisi, possessing a very high concentration of centenarian olive trees. It is therefore not difficult to imagine the spectacle left by the passage of xylella fastidiosa, which has caused the loss of more than a third of the trees in this iconic place. The bacterium has also struck much larger areas, causing what has been described as an “ecological disaster”: entire fields devastated and large olive trees without foliage, with bare, dead branches. A severe blow, both to the landscapes of Apulia and to the farms that found themselves with land contaminated by the bacterium, a drastic drop in production, and the resulting economic losses. These difficulties persist, exacerbated by unfavorable climatic conditions. And they are reflected in the olive oil industry of all of Italy, which has now fallen to fifth place among olive oil-producing countries.
The search for solutions
Carried by an insect measuring just a few millimeters, the philaenus spumarius, the bacterium xylella fastidiosa attacks olive trees by reproducing until it clogs the sap-conducting system, these vessels through which water and minerals also pass. This causes the drying out first of the leaves, then of the branches, and finally of the entire plant, which dies, sometimes in less than a year. According to Save the Olives, an NGO of volunteers including agronomists, farmers, researchers, students, and entrepreneurs, engaged for years in supporting research projects and actions to combat the spread of the bacterium, the plague is progressing at a speed of 2 kilometers per month. There are 145,000 square kilometers of land in Apulia at risk of desertification. However, there are no proven treatments or cures.
Although the scenario is discouraging, many people like Giovanni Melcarne have refused to resign since the beginning of the crisis. They have sought ways to counter the bacterium. For example, by participating in genetic improvement projects to find resistant cultivars. “I have been collaborating with the CNR in Bari on a genetic improvement plan for olive trees for six years, and we have gradually increased the number of crossings we do in a year. We have ad hoc facilities, like a climate chamber, and a field with 400 varieties where we test resistance to the combination of xylella and water stress. Part of my olive grove is dedicated to these trials.”
He also explains the search for varieties that are resistant to the combination of xylella fastidiosa and water stress. Climate change, in fact, is making water increasingly scarce. “Temperatures are much higher, and thus water consumption tends to increase. I am convinced that in the future, we will have to produce oil from olive groves in aridiculture, both for cost reasons and for the lack of water. That’s why we are conducting these combined tests.”
A new hope
The work of centers of excellence in research, such as the CNR and the University of Bari, in collaboration with highly innovative companies and farms like Melcarne's, has produced results that have breathed new hope into the olive growers of the region. The process to declare a resistant variety is complex and time-consuming: indeed, laboratory tests are not always sufficient to assess the behavior of a cultivar*, and plants must go through a complete cycle in the field exposed to natural conditions to truly prove their resistance. However, four resistant, or at least tolerant, varieties to xylella fastidiosa have already been identified and developed. Thousands of young plants of these varieties have therefore been planted in the fields, in place of olive trees that had been uprooted in an effort to stop the advance of the disease. And in the Plain of Millennial Olive Trees, efforts are being made to save the large trees by betting on “cohabitation” with the bacterium through grafting with resistant varieties.
Resistant olive trees, for the entire Mediterranean
The name of Apulia has thus often been associated with that of the olive tree plague in recent years. International media have eagerly reported on the spread of the bacterium in Italian olive groves. Melcarne hopes that soon his land will be celebrated as “the mother of the renewal of olive cultivation, thanks to these cultivars capable of resisting today’s threats.”
Moreover, the results of research and collaboration between the public and private sectors in the fight against xylella fastidiosa benefit not only the Apulia region. In Spain, the world's largest producer of olive oil, where the bacterium has also been detected, the research from the University of Bari brings hope. By developing varieties like the "lecciana", specially adapted to super-intensive olive groves and resistant to the bacterium, Italian researchers and olive growers are actively contributing to the defense of a flagship crop of Mediterranean countries.
* a plant resulting from selection, mutation, or hybridization, whether natural or induced, and cultivated for its agricultural qualities. (source Larousse)
Cover photos: the "centenarians" are also threatened © Achim Ruhnau - Pixabay