Resistance to Haustorial Development of Two Mistletoes, Amyema preissii (Miq.) Tieghem and Lysiana exocarpi (Behr.) Tieghem ssp. Exocarpi (Loranthaceae), on Host and Nonhost Species

Abstract

Seeds of two mistletoe species, Amyema preissii and Lysiana exocarpi, were inoculated onto host and nonhost species, and haustorial development was examined. Resistance to haustorial penetration was observed in the bark and xylem. Bark resistance took one or all of three forms: (1) mechanical resistance; (2) production of wound periderm; and (3) abnormal changes in host tissues surrounding the mistletoe haustorium. Xylem resistance included physical constraints on haustorial growth and abnormal changes in host tissues surrounding the haustorium. Bark resistance to A. preissii occurred on all nonhost species, and mistletoe haustoria failed to penetrate the bark of all nonhost species except Geijera linearifolia. In the latter case, A. preissii haustoria reached host xylem, but further development was hindered by xylem resistance. No resistance was recorded on Acacia nyssophylla, the host species of A. preissii. Bark resistance to L. exocarpi was observed in haustoria growing on the two major host species, Heterodendrum oleifolium and Myoporum platycarpum, and haustorial development on these two species was delayed for up to 3 mo compared with other host species. While no bark resistance was observed in haustoria growing on the three nonhost species, Exocarpos aphyllus, Eucalyptus oleosa, and G. linearifolia, all three species showed resistance by the xylem to haustorial development. No xylem resistance, however, was recorded on the three host species, A. nyssophylla, H. oleifolium, and M. platycarpum.