Translocation relationships in and between mistletoes and their hosts

Abstract

Studies of translocation between mistletoes and their host trees were conducted under natural conditions in various California locations. Both dwarf (Arceuthobium spp.) and green (Phoradendron spp.) mistletoes were studied. Various labeled materials were used, including C14O2, several G14-labeled herbicides, and P32 and S35 (as phosphate and sulfate, respectively). The C14-labeled assimilates and the P32 translocated from host foliage into dwarf mistletoes growing on the host branches, but no such movement occurred from host branches to the mistletoes. When P32O4 was applied to the wood of the host branches, beneath the infections, P32 appeared in both dwarf and green mistletoes. This type of application apparently was a highly effective means of introducing the labeled phosphate. Labeled substances applied to the shoots of dwarf mistletoes normally moved apically. In a few instances, P32 was found to move basally into the endophytic system and host branch. This movement was not through living tissues, however, because it was not blocked by killing the basal parts of the mistletoe shoots with steam. Translocation in green mistletoes differed from that in dwarf mistletoes. In the green species, labeled assimilates and P32 were transported basipetally into the endophytic systems. However, label did not move from the green mistletoes into the host branches.