Studies on the infestation by Phytophthora spp. affecting oak seedling production in forest nurseries in Sardinia (Italy)

Abstract: Quercus ilex and Q. suber are the main forest species grown in Sardinia nurseries. Between 2013 and 2016, seedlings of both oak species were sampled to detect Phytophthora species, one of the most important groups of pathogens in nursery environment. Root and soil samples were collected from both asymptomatic and symptomatic potted plants in two forest nurseries located in North Sardinia. In addition, potting soil and irrigation water were sampled. Isolations from soil and plant materials were made with fresh oak leaves as baits and using Synthetic Mucor Agar (SMA), a selective medium for Phytophthora. Isolates were identified based on a combination of morphological and DNA sequencing analyses. In total, three known Phytophthora species were detected. Phytophthora cinnamomi was the species with the highest detection rates, followed by P. cryptogea and P. plurivora, and a new species currently under taxonomic description. The overall percentage of samples positive for Phytophthora isolation averaged 80%. At one nursery, 100% of the sampled seedlings were positive, with most of the plants remaining asymptomatic. The high level of Phytophthora infestation rate has seriously compromised the production of oak seedlings in these nurseries. Best management practices for reducing the risk of introduction and dispersal of Phytophthora spp. outside nurseries need to be undertaken.