Portugal detects Xylella in citrus for the first time in the EU and the focus of ‘Oriental fly’ is consolidated in Italy

Last December the Government of Portugal updated the demarcated area for the Xylella fastidiosa in the metropolitan area of ​​Porto. And for the first time in Europe, not only was the presence of this bacterium confirmed in citrus, but it was pointed out that the infection had occurred with a subspecies -the fastidious X. fastidious– very rarely described for this crop. To this disease, the fight for which is classified as a “priority” by EU regulations, we should add another threat equally located in the ‘top 20’ of foreign pathogens with the greatest economic, social and environmental impact: the consolidation of the focus from ‘Oriental fruit fly’ (Bactrocera dorsalis) detected this past summer in southern Italy, which also affects citrus. A third “priority” disease has been stalking this crop since 2018, this time from the southern shores of the Mediterranean, in Tunisia. A recent study by the Valencian Institute for Agricultural Research (IVIA) has just demonstrated, with mathematical models and in an irrefutable way, that this fungus –repeatedly detected in consignments imported from Argentina or South Africa- is perfectly capable of settling in the European Mediterranean areas. Given the seriousness of the situation generated by these and other major threats to the sector –such as the presence of the two HLB vectors in Portugal (Trioza erytreae) and in Israel (Diaphorina citri)- The Citrus Management Committee (CGC) speaks openly that the Spanish citrus sector lives in “a state of permanent phytosanitary alert”.

The results of the Portuguese laboratory indicate that the citrus fruits affected by the Xylella fastidiosa could have been infected by the subspecies annoyingdifferent from the multiplex that affects almond trees in Alicante but is also present in Mallorca. Given that this subspecies is associated with Pierce’s disease in the vine and with the foliar scorch of the almond tree in America and not with Variegated Chlorosis of Citrus -which is linked to another, the pauca, also present in Ibiza and Italy- it is it would be a subtype that rarely affects citrus. The fastidious X. fastidious, in fact, it had only been described exceptionally by some authors for certain species of rutaceae. The Xylella is a bacterial pathogen transmitted by vectors -very abundant in all citrus-growing areas- and associated with serious diseases in a wide range of vegetables. More than half a thousand plants may be hosts of the disease -most of them wild, as many ornamentals and some fruit trees- but so far in the four European countries where it had been confirmed (Italy, France, Portugal and Spain) it had only been detected at 174, none of them from the citrus family. Each subspecies has a ‘predilection’ for a type of plant, producing symptoms in them that may be similar or different, hence the importance of a reliable genetic determination.

Of identical severity could be cataloged the new source of Bactrocera dorsalis confirmed in southern Italy this summer. It was not the first incursion into the EU but it was the most relevant. The ‘Oriental Fly’ was also detected in the Campania region as early as 2018 and subsequent findings were made in France. The monitoring carried out in the transalpine country has now confirmed that the insect is multiplying in orange fields and other fruit trees in the area.

The ‘Oriental Fly’ belongs to the Tephritid family, to which the ‘Mediterranean Fly (Ceratitis capitata) –which is endemic to Spanish citrus-growing areas- but is even more aggressive and polyphagous. The coexistence of both would aggravate the resistance problems that already occur with the few authorized phytosanitary products, it would trigger spending on treatments, it would make it necessary to investigate and design a biological fight different from the one already implemented for the ‘Ceratitis’ (based on the release of sterile males and use of pheromones) and could lead to new export restrictions.

To these pathogens we should add another equally classified as “priority”, the ‘False moth’ (Thaumatotibia leucotreta). The CGC has repeatedly denounced and as a member of Intercitrus transferred it to the representatives of the European Commission (EC) in November, that the cold treatment approved in June for imports of oranges from countries with False moth, was breached by South Africa during its last export campaign. As was also clarified in the aforementioned visit to Valencia, the required temperatures were not applied or monitored where the standard determines -in the fruit pulp- but at the ‘ambient’ temperature of the container (so the treatment is not effective ).

A fifth disease, also in the ‘top 20’ of those with the greatest impact, is repeatedly detected in European port controls on citrus imports from Argentina, South Africa or Brazil: ‘Black spot’ (Phyllosticta citricarpa). In 2019, after many years of scientific debates and some studies (promoted by South Africa) in which its ability to adapt to the Mediterranean was denied, the fungus was detected in citrus farms in Tunisia. A recent article from the IVIA, which had previously stated that it was capable of doing so, has accredited in collaboration with the Higher Institute of Agronomy of Chott Mariem in Tunis that “climate is not a limiting factor for the establishment and spread of this disease ” in the Mediterranean area. The conclusions of the study, in which infections in all citrus-growing regions were simulated using mathematical models, are now certainly indisputable.

From farm to table

The European strategy ‘From the farm to the table’ –derived from the Green Pact approved by the EC- maintains some quantified objectives of reducing the use of chemical pesticides by 50% in eight years. Since the beginning of this century, up to 16 foreign pests and diseases have been introduced into Spanish citrus. In this regard, the CGC fully agrees with the position expressed in the Council of Agriculture Ministers of the EU on December 20, which demanded from the EC a complementary evaluation of the impact of this measure. Indeed, he shares the need to rationalize pesticides but claims that, given the seriousness of the damage caused by already known pathogens and those that threaten to arrive, the consequences that the elimination of active materials will have, not only for control of pests – due to losses, economic losses and yield drops – but also due to the resistance that can be generated (by repeating treatments with the few substances that remain). Secondly, it calls for measuring and harmonizing transition times to reconcile the progress of biological control, still in its infancy, with the gradual withdrawal of these products.

Portugal detects Xylella in citrus for the first time in the EU and the focus of ‘Oriental fly’ is consolidated in Italy