Infection patterns and hosts of Arceuthobium oxycedri (DC.) M. Bieb. in Slovenia

Abstract

SummaryEleven mixed populations of Juniperus oxycedrus L. and Juniperus communis L. were inventoried for the presence of parasitic woody species Arceuthobium oxycedri (DC.) M. Bieb. infections. Both J. oxycedrus and A. oxycedri are rare and distributed in marginal populations in Slovenia. To our knowledge, this is the first detailed research on the host species as well as on the infection and spreading patterns of A. oxycedri in Europe. Assessment of the infection rate was based on the Hawksworth six‐class dwarf mistletoe rating system (DMR). The dimensions of A. oxycedri specimens were surprisingly large and often exceeded 25 cm in diameter, the largest even measuring up to 40 cm. Six juniper populations of 11 were infected, and the proportion of infected host individuals in these ranged between 29.17 and 82.93%. The proportion of infected J. oxycedrus specimens in infected populations was 76.56%, while this percentage for J. communis was 54.90%, which is surprisingly high for this species. A different pattern of infection was observed for the two hosts. A typical infection on J. communis was more localized. Usually, only a single infection was present and was most common on the trunk in the middle third of the crown and much less common on the branches. In J. oxycedrus, infections were also most common in the middle third, but also frequent in other areas of the trunk as well as on the branches. Mostly, we observed a dotted pattern of infection with uninfected areas in between. We assume that A. oxycedri will continue to slowly spread in Slovenia, primarily in areas where it is already present. However, its control is probably not yet necessary.