PARTITIONING OF ALLOZYME DIVERSITY IN WILD POPULATIONS OF MALUS-SIEVERSII L AND IMPLICATIONS FOR GERMPLASM COLLECTION

One of the primary progenitors of the cultivated apple is Malus siever sii L., a species native to the forested regions of central Asia. Desp ite the horticultural importance of M. sieversii, little is known abou t genetic variation in this species. In this study, allozyme diversity at 18 loci was determined for 259 seedlings belonging to 31 sib famil ies, each consisting of the set of offspring from a different open-pol linated maternal (seed) parent. Maternal parents belonged to 14 popula tions from four geographic regions. Genetic diversity statistics were computed from the resulting allele and phenotype frequencies. Cluster analysis of sib families showed that there was some grouping based on geographic region, but 16 of the sib families were most closely relate d to sib families from other regions. Analysis of molecular variance ( AMOVA) indicated that 85% of the enzyme variability was due to differe nces among sib families within populations and 15% was due to differen ces among regions. No variability could be assigned to differences amo ng populations within regions. In addition, no alleles were found that were fixed in a region and unique to that region. These results sugge st that plants belonging to M. sieversii effectively form a panmictic population. Consequently, a thorough sampling of a few large populatio ns will efficiently capture most of the genetic diversity present in w ild M. sieversii.