Genetic variation within the Pachycladon (Brassicaceae) complex based on fluorescent AFLP data

Abstract

Species within the Pachycladon complex (Cheesemania fastigiata, C. sp., C. stellata, C. wallii, C. latisiliqua, Pachycladon novae‐zelandiae, Ischnocarpus novae‐zelandiae, and I. exilis) have limited dispersal ability, exist in small isolated and sparsely distributed populations, and have a predominantly selfing breeding system with low pollen‐ovule ratios. Amplified fragment length polymorphism (AFLP) was used to characterise genetic diversity within the complex. A binary matrix of 749 AFLP characters was generated for analyses, of which 739 (98.66%) were polymorphic. Within‐population genetic diversity was assessed based on Shannon's index (I) (average 0.1400) and percent polymorphic loci (P) (average 27.84), which were moderate to high for selfing species. Percent polymorphic loci at the species level for C.fastigiata and P. novae‐zelandiae (40 and 42%, respectively) were similar to selfing species with regional distribution or mixed mating species with endemic distribution based on comparison with other studies. However, the % polymorphic loci for I. novae‐zelandiae (79%) was much higher than expected. The proportion of genetic diversity found among populations (GST) for C. fastigiata (0.6698), and I. novae‐zelandiae (0.7998), was higher than in other studies of selfing species, suggesting that gene flow has been limited. Although sample size was small in this study, strategies are suggested for the genetic conservation and management of species within this complex. Cluster analysis and principal coordinates analysis of the AFLP data revealed two main groups of taxa: (i) Pachycladon and Cheesemania and (ii) Ischnocarpus. It is concluded that the circumscription of these three genera needs to be re‐examined. It was inferred from population genetic data that a population of Cheesemania from the Chalk Range, Marlborough, is as distinct as any of the named species and warrants further taxonomic investigation.