Amber Faust - Botany 2010

Identification of host cues for haustorium orientation and initiation in the leafy mistletoe Phoradendron serotinum (Santalaceae). Co-authors: Ryan L. Reid, Angela K. Hawkins, Sara E. La Roya, Brandi C. Cannon, Timothy J. Verastegui, Victor G. Tarson, Lindsey D. Garza and Christopher P. Randle

A previous pilot study by demonstrated that Phoradendron serotinum seedlings establish haustorial connections following in vitro germination in 3% hydrogen peroxide. The rate of successful haustorial formation was independent of the age of growth of a woody stem of a known host (Quercus nigra); haustorial establishment occurs with non-distinguishable frequency on second year growth (branches) or old growth (trunks). However, haustoria did not form when germinated seeds are planted on killed wood (logs). This indicates that host cues differ among living and dead tissues. In the present study, we test three hypothetical host cues for successful growth and establishment of haustoria: A) light cues, B) chemical cues associated with the host cork, and C) gaseous cues emanating from living hosts. Three experiments were preformed to test each of these hypothetical cues independently A) by shielding germinated embryos from light during growth, B) by insertion of a non-permeable, but transparent substance between the embryo and the host, and C) by testing the ability of an embryo to orient haustorial growth toward a living twig 5mm distant. Experiments each consisted of 100 replicates at two sites germinated in 3% hydrogen peroxide and planted during late winter. Haustorial growth and establishment was monitored weekly for 16 weeks.

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