Growth of Longitudinal Strands of Phoradendron juniperinum (Viscaceae) in Shoots of Juniperus occidentalism*

Abstract

To quantify the development of the mistletoe Phoradendron juniperinum within the branches of its host, Juniperus occidentalis, the growth of longitudinal (cortical) strands was measured. To begin, infections were classified positionally as either lateral (attached along sides of branches) or pseudoterminal (secondarily occurring at ends of branches). For both infection types five shoot dry weight classes were established, allowing comparisons, of growth of longitudinal strands to shoot dry weight. For lateral infections of all weight classes longitudinal strands showed greater basipetal than acropetal growth. In early stages of seedling establishement endophytic system spread is emphasized over shoot growth while in older plants shoot growth is emphasized; this feature is reflected in the dramatic decrease in spread/weight values over time. Comparisons between lateral and pseudoterminal infections of all weight classes revealed that lateral infections extend greater distances within host bark. Absorptive efficiency values were calculated. The determination of spread/weight and absorptive efficiency values represents a novel approach to endophytic system study that has applicability in physiological and ecological studies as well as in mistletoe-control methods