An assessment of Italian olive trees infected with Xylella fastidiosa has shown that whilst symptoms may be reduced, treatments do not eliminate the pathogen from infected plants.
Some trees in Italy’s olive growing heartland Puglia have been treated in a bid to contain and prevent the bacterial disease from spreading across the region and decimating southern Italy’s olive sector.
Although some treated plants have shown visible signs of improvements such as growing more leaves per branch and producing consistent olive yields, the disease is still present.
Over several months researchers from the University of Foggia and a council for agricultural research in the agrarian economy, CREA, have been analyzing treatments and have now passed on some of their assessments to the European Food Safety Authority’s Panel on Plant Health.
The Panel also examined treatments used elsewhere to control bacterial infections in citrus, apple, pear and grape vines.
The Foggia researchers treated infected olive trees with several bioactive compounds following severe pruning. A commercial product containing zinc, coppers and citric acid was also used and all treated plants survived the winter period.
But, despite what appeared to be symptomatic improvements, trees are still infected and the Panel’s report says it is too early to draw conclusions on the long-term effectiveness of such treatments from these experimental results.
"Despite the reported more vigorous growth and healthy appearance, the treated olive trees are still systemically infected by X. fastidiosa, and could be acting as sources of inoculum for insect vectors which might be even more attracted to plants showing good vegetative conditions," says the EFSA report.
"The treatments under consideration may reduce the symptoms of X. fastidiosa in olive trees, but do not eliminate the pathogen X. fastidiosa from the treated plants. There is currently no treatment to cure plants.
"The positive effects from good crop management practices applied in combination with the treatments under evaluation may have contributed to the reported vigorous growth and improve the appearance of the diseased plants."
Panel experts note that more experiments are needed.