Biological and epidemiological aspects of the quarantine pathogen Phytophthora ramorum

Abstract

Phytophthora ramorum is a quarantine pathogen that causes leaf blight and shoot dieback of the crown, bark cankers and death on a number of both ornamental and forest trees, especially in North America and northern Europe, where it has produced severe outbreaks.
In Italy it was first reported in 2002, on Rhodondendron yakushimanum in a Piedmont nursery; after that it seemed to have disappeared, only to re-emerge in 2013 when numerous isolates were detected on batches of Viburnum tinus plants growing in some nurseries in the Pistoia area (Tuscany), which is an important district in the trade of nursery plants world-wide. This work reports on a number of laboratory tests that were carried out on isolates from infected plant samples. The micromorphological and macromorphological characteristics of the pathogen growing on carrot agar (CA), corn meal agar (CMA), malt extract agar (MEA) potato dextrose agar, and V8 agar with added PARPNH (see text) were determined, as was the growth rate at 10º, 15º, 20º, 25°, 30º, 32º and 35ºC. Molecular analysis was employed to identify the isolates more precisely. Inoculation trials under the bark were also carried out to ascertain the isolate virulence and the Koch’s Postulates.
The Plant Protection Service of the Tuscan Region (SFR, Servizio Fitosanitario Regionale) was alerted as soon as the pathogen infection was detected and it took the prescribed steps to eradicate the infection in the field and prevent the recurrence of an epidemic.