Haustorial development and growth benefit to seedlings of the root hemiparasitic tree Nuytsia floribunda (Labill.) R.Br. in association with various hosts

Dry matter gains and haustorial production of pot-cultured seedlings of Nuy tsia floribunda were assessed after a 12 month period of association singly with each of a range of potential woody host species. One species, Adenant hos cygnorum, of similar size to most parasitized hosts, served as measure of response of Nuytsia in a non-benefiting situation. Rated on this basis, all 23 parasitized hosts elicited greater mean dry weights of Nuytsia than when on Adenanthos, and seven of these instances were highly significant. N umbers and weights of penetrating and presumably functional haustoria forme d on a host were broadly correlated with growth benefit to Nuytsia, but the re were notable instances of unusually poor or great benefit from a host re lative to the complement of haustoria involved. Experiments in which hausto ria-bearing associations of Nuytsia partnered with nodulated Acacia hosts ( Acacia acuminata and A. cyclops) were fed N-15(2) showed significant transf er of N-15 to the parasite, but failed to determine whether the label had b een acquired through haustoria or directly by Nuytsia roots following turno ver of nodule and root residues of the host in the rooting medium. A parall el study using the unusual non-protein amino acid, djenkolic acid, as a mar ker of benefit from the djenkolic acid-containing host. A. cyclops, showed appearance and progressive build-up of the compound in foliage of Nuytsia o ver a 6 month period after partnering the species in pot culture. Presence of the compound at final harvest in xylem sap of both partners but not in s oil solution of the cultures strongly indicated xylem transfer via haustori a as the principal avenue for N benefit to the parasite. Results are discus sed in relation to a recent evaluation of haustorial structure and function ing of N. floribunda. (C) 2000 Annals of Botany Company.