During his time at the USDA, Pierce began investigating a mysterious disease that was affecting California's vineyards in the 1880s. This disease caused a wide range of damages, including leaf withering, yellowing, root rot, and sudden vine death. These symptoms had severe consequences, leading to significant losses in grape production and the destruction of vineyards. Pierce's exceptional contribution was to identify the causative agent of this disease. Through meticulous observations and in-depth research, Pierce identified the Xylella fastidiosa bacterium as the culprit. This microorganism, a transmissible phytoplasma, spreads through the plant's phloem, the tissue that transports water and nutrients. Once infected, the vine displayed symptoms of rot and sudden death.

Xylella fastidiosa and Its Spread
Xylella fastidiosa is a cunning bacterium that can be transmitted from one plant to another by sap-sucking insects. Insects acquire the bacterium by feeding on infected vines and spread it as they move to other plants. This mode of transmission makes disease control a formidable challenge.

The European Threat
Recently, the threat of Pierce's disease has arrived in Europe, causing increasing concern. The first cases of Xylella fastidiosa on wine vines were recorded in Majorca.
A variant of the microorganism has been identified, Xylella fastidiosa fastidiosa, which includes strains responsible for Pierce's disease in grapevines but is capable of infecting almonds, maples, cherries, broom, and alfalfa. There is also a strain that causes diseases in Cercis occidentalis. Understanding the broad spectrum of host plants of this bacterium is essential for effective disease management and preventing its spread in various agricultural and natural environments. Currently, the disease has also been found on vines in Portugal, in ten different locations within three municipalities in the Porto area. Unfortunately, Xylella has been identified on other plant species in various European regions, including Corsica and the French Riviera in France, Saxony in Germany, the Balearic Islands, and the Valencia region in Spain.

The Role of Vector Insects
A critical aspect of disease spread is the role of vector insects. In Apulia, Xylella fastidiosa spread through the spittlebug, known as Philaenus spumarius, recognizable by the foamy masses produced by nymphs and nymphs (the young developmental stages of insects) found on stems and leaves. While this insect is not present throughout Europe, unfortunately, potentially, all insects that feed by sucking raw sap from the xylem vessels of plants could be carriers of Xylella. This bacterium settles in the xylem vessels and can cause the desiccation of plants, and, therefore, insects that feed from these sources can come into contact with the bacterium.

Legacy and Ongoing Research

The legacy of Newton B. Pierce was to significantly contribute to understanding this devastating disease and identifying its pathogenic agent. His work laid the foundation for future research on how to address Pierce's disease and protect vines from the harmful effects of Xylella fastidiosa. Research continues to find better ways to prevent, control, and manage Pierce's vine disease. As this disease still threatens grape cultivation throughout Europe, the legacy of Newton B. Pierce endures through the efforts of modern phytopathologists and researchers. His dedication to science and protecting agricultural crops remains a source of inspiration for those striving to preserve vines and the wine industry for future generations.

Virgilio Vidor, un maestro di sviluppo locale e viticoltura tropicale in america centrale