Establishment of the Mistletoe Phoradendron macrophyllum: Phenology of Early Stages and Host Compatibility Studies

The timing and morphological characteristics of the early stages in the establishment of Phoradendron macrophyllum (Viscaceae) on Salix laevigata were observed and quantified using clonal host material in greenhouse conditions. Observed stages were seed germination; holdfast formation; renewed greening of mistletoe tissue; swelling of the underlying host branch; aerial shoot formation; and development of the endophytic system. Aerial shoot formation was influenced by local moisture availability, but other stages in establishment were independent of water or nutrient sprays. When seeds of P. macrophyllum were placed on cuttings of Eucalyptus (a host susceptible to certain loranthaceous mistletoes, but not susceptible to Phoradendron), seed germination and hypocotyl swelling took place, but no further stages in holdfast formation occurred. A corky layer, or wound periderm, formed locally beneath the mistletoe seeds. When viscin alone from Phoradendron seeds was placed on Eucalyptus stems, wound periderm formation was also triggered.