Phytophthora infestans populations in Italy – Plant Pathology highlight.

Phytophthora infestans caused the Irish famine in the 1840’s and remains a global threat to food security.  Jean Ristaino and colleagues at NC State University have been studying global populations for many years.  Her lab identified and named the historic lineage FAM-1. The FAM-1 lineage caused outbreaks of potato late blight in the United States in 1843 and then two years later in Great Britain and Ireland. FAM-1 caused massive and debilitating late-blight disease outbreaks in Europe, leaving starvation and migration in its wake. She also documented the spread of the lineage to five continent and its global presence for more than 140 years. Ristaino theorizes that the pathogen arrived in Europe via infected potatoes on South American ships or directly from infected potatoes from the United States.

Fig. 1. Late blight on tomato fruit.

The disease is not simply of historical interest. It currently causes annual losses on both potato and tomato and is responsible for widespread use of fungicides to control the disease (Fig 1). In a study recently published in the BSPP journal Plant Pathology, Ristaino and colleagues studied the populations of the pathogen on both crops in Italy and nearby Mediterranean countries. In 2018, she was awarded a Fulbright Award by the US Department of State and traveled to Sicily. The Fulbright Award provided an opportunity for her to work with colleague Dr. Santa Olga Caciola at the University of Catania in Italy who works on Phytophthora infestans and other Phytophthora diseases including citrus Phytophthora’s.  Phytophthora infestans still wreaks havoc including on Italy’s prized tomato fruit crop.  She expanded the network of scientists in Italy and North Africa that sampled for late blight and her lab studied the strains collected back in the US. There is significant trade between Sicily and the EU and North Africa, which is one way new and re-emerging diseases spread.  With colleagues at the University of Catania, and collaborators throughout Italy, the team sampled the pathogen in the North and South on both crops.

The populations were compared to those in the Euro Blight and USABlight databases and four lineages of the pathogen were identified. The 13_A2 (Blue 13), 2_A1, 23_A1, and 36_A2 lineages were found. Two other isolates collected could not be matched to any currently known clonal lineage. The team documented the first report of 36_A2 in Italy. Two isolates from Solanum nigrum were 13_A2, suggesting this weed host could be a reservoir of inoculum. The 23_A1 lineage was found widely on infected tomato crops in Italy and is the same as the lineage US-23 that is widespread on tomato and potato in the North America.

Fig 2. Participants in Phytophthora Diagnostic’s workshop held at the University of Catania, May 2018. Jean Ristaino, far right and Santina Cacciola third from right, first row.

Dr. Ristaino also led a Phytophthora diagnostics training workshop with colleagues while at the University of Catania that trained 30 students from many EU countries (Fig 2). Building multiple institutional capacity in Phytophthora diagnostics and empowering women scientists was an important goal of her work. In part for her science and her efforts to build a worldwide network of well-trained diagnosticians, she won the American Phytopathological Society’s Excellence in International Service Award in 2016 and in 2020 became a Fellow of the American Phytopathological Society and the American Association for the Advancement of Science

Fig 3. Salvatore Scalco, founder of the National Fruit Company in Washington DC, Jean Ristaino’s maternal grandfather and her mother seated on a truckload of Gros Michel bananas donated to the Red Cross, 1925.

Her research project in Italy is particularly poignant because her maternal grandparents emigrated in the 19th century from Sicily to the US and settled in Washington DC. They were both born in the small Sicilian town of Cefalù.  Two generations back her ancestors were farming citrus fruits, tomatoes and vegetables in Italy.  After immigrating to the US, her grandfather, Salvatore Scalco, began selling fruits and vegetables and eventually opened the National Fruit Company in Washington (Fig. 3).

Amanda C. Saville, Federico La Spada, Roberto Faedda, Quirico Migheli, Bruno Scanu, Paolo Ermacora, Giovanna Gilardi, Giorgia Fedele, Vitorrio Rossi, Nicolo Lenzi, Antonino Testa, Mohamed Bechir Allagui, Marwa Moumni, Enza Dongiovanni, Fatma Zohra Rekad, David E. L. Cooke, Antonella Pane, Santa O. Cacciola and Jean B. Ristaino published this study in Plant Pathology:

Population structure of Phytophthora infestans collected on potato and tomato in Italy

TITLE IMAGE: Phytophthora infestans on a potato plant. All images used with permission of the author