Host-race specificity in the endemic pygmy mistletoe Korthalsella salicornioides (Viscaceae) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Biology at Massey University, Palmerston North, New Zealand

Abstract

Korthalsella Tiegh. is a genus of stem hemiparasites in the family Viscaceae, represented in New Zealand by three endemic species: K. clavata, K. lindsayi, and K. salicornioides. The most host-specific is K. salicornioides as it parasitizes two main host genera Leptospermum (Myrtaceae) and Kunzea (Myrtaceae), while the other two species are considered generalists parasitizing a wider range of host species. K. salicornioides is naturally uncommon and sparse, although it can be locally abundant on occasion. Mistletoe populations are at risk primarily due to habitat destruction and subsequent loss of hosts. Cross-infection experiments in K. salicornioides provided some insight into the presence of putative host races, as better mistletoe seedling establishment success rates were apparent when the maternal and recipient hosts were the same. However, because previous molecular sequence data (nuclear internal transcribed spacers and chloroplast trnQ-rps16) for K. salicornioides were not informative about specific host-races, more rapidly evolving molecular markers might be expected to detect host races. In this study, next generation sequencing was used to develop novel microsatellite markers for Korthalsella. Eleven markers were reliably amplifiable and the most polymorphic for K. salicornioides were used to genotype 272 K. salicornioides individuals from 16 populations. Across all populations few alleles were identified, and within-population assessment of genetic variation indicated that many populations have low levels of genetic diversity and high proportions of homozygotes. Despite the presence of few alleles, a high degree of genetic differentiation between most populations was detected and was found to reflect host species and geography. The findings of this study that Korthalsella salicornioides populations have low levels of genetic variation but host-specific races, has important conservation implications. The main conservational focus should be maintaining and increasing host Leptospermum and Kunzea populations. The spread of mistletoe seed on hosts within or between populations may also increase the chances of continued survival. However, it is imperative that genetic material comes from the same host species, and consideration should also be given to the geographic area, especially in the Wairarapa. This study provides insights into the population structure within and between the different host populations and suggests several interesting areas of future study.