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Host range, host specificity, regional host preferences and genetic variability of Korthalsella Tiegh. (Viscaceae) mistletoes in New Zealand

ABSTRACT The distribution of parasitic plants is governed by the availability and distribution of suitable host species. Here we report the distributions, host associations and genetic variability of the three endemic New Zealand species of Korthalsella (Viscaceae) mistletoes. These species differ in their primary host and in the breadth of secondary and tertiary hosts. Korthalsella salicornioides is the most host-specific, with 96% of the total records from the primary (Leptospermum scoparium s.l. [Myrtaceae]) and secondary (Kunzea robusta [Myrtaceae]) hosts, but 26 host taxa (six genera in five families) recorded overall. Korthalsella clavata and K. lindsayi are more generalist species, parasitising 44 taxa (19 genera in 14 families) and 42 taxa (13 genera in 11 families), respectively. For K. clavata, Coprosma propinqua (Rubiaceae) and C. dumosa are the primary and secondary hosts, respectively, representing 66% of the total records. For K. lindsayi, Melicope simplex (Rutaceae) is the primary host (26% of records), whereas Coprosma crassifolia, Lophomyrtus obcordata (Myrtaceae), Myrsine australis (Primulaceae) and M. divaricata are secondary hosts. The only overlap among hosts is at the tertiary level, with K. clavata and K. lindsayi sharing Coprosma rigida and C. virescens, and among hosts that are rarely parasitised. Korthalsella salicornioides is the most widely distributed species occurring widely on the North and South Islands, while K. clavata is rare in the North Island and K. lindsayi is rare in the western regions of the South Island. Comparative sequencing of nuclear internal transcribed spacers and plastid trnQ–rps16 for the three mistletoes revealed that within-species genetic structure is geographic rather than host-based. Additionally, some plastid haplotypes and ITS sequence types shared between K. clavata and K. lindsayi may result from local hybridisation and introgression between the two species in a few locations.