Seeds capture the diversity of genetic resource collections of Malus sieversii maintained in an orchard

Abstract

Many species in genebank collections are maintained vegetatively either as in vitro cultures or as plants in the field or greenhouse. In these cases, individual genotypes (cultivars) are the focus of conservation. In crop wild relatives, where the value of an accession is in the heterogeneity of segregating genotypes, seeds may be the most representative form of conservation. We used two sets of field-planted Malus sieversii apple trees that originated from seeds collected from two wild populations in Kazakhstan as a model system to determine if seeds from hand-pollinated crosses could be used to represent the allelic diversity of the parent trees in a genebank orchard. A crossing design was developed that used each of the selected trees from the two Kazakhstan collection sites as mothers and also as fathers in the form of bulked pollen pools. The sets of offspring from these crosses were genotyped using microsatellite markers. Paternity analyses revealed the percentage of offspring that was derived from each of the parent trees. We also determined the contribution of each parent to the fertilization events from the pollen pools. Although there were some unintended pollination events (fertilization by trees in unexpected pollen pools) and unequal contribution of pollen parents within pollen pools, we demonstrated that the seedlings effectively captured the allelic frequency and diversity of the parents. A seed collection strategy is the most efficient way to conserve the diversity of crop wild relatives even in collections typically conserved as individual clones.