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

item Volk, Gayle
item Henk, Adam
item Forsline, Philip
item Szewc-Mcfadden, Amy
item Fazio, Gennaro
item ALDWINCKLE, HERB - Cornell University
item Richards, Christopher

Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2016
Publication Date: 10/5/2016
Citation: Volk, G.M., Henk, A.D., Forsline, P.L., Szewc-McFadden, A.K., Fazio, G., Aldwinckle, H., Richards, C.M. 2016. Seeds capture the diversity of genetic resource collections of Malus sieversii maintained in an orchard. Genetic Resources and Crop Evolution. doi:10.1007/s10722-016-0450-8.

Interpretive Summary: The USDA-National Plant Germplasm System (NPGS) apple collection is maintained primarily as trees in the field in Geneva, NY. It is expensive to maintain safety duplicates of these plants at a secondary location; however, in some cases seeds may best represent the portion of the collection that is representative of crop wild relatives because seeds efficiently capture many unique genetic combinations. Two sets of Malus sieversii apple trees in the NPGS field collection were originally collected as seeds from two distinct populations in Kazakhstan. Hand pollinations within each of the sets of trees were performed to determine if the seeds resulting from these crosses captured the diversity of the parents. Seeds were collected from these crosses and grown into seedlings. Leaves were sampled and DNA fingerprinting analyses were performed. The genetic analyses revealed that the seedlings were not always of the expected parentage, likely due to a significant level of pollen cross-contamination. Despite the unexpected parentage of some seedlings, the sets of seedlings successfully captured the measured diversity of the parents. We conclude that our seed collection strategy could be used within genebanks to produce seeds that are representative of wild species diversity within collections that are traditionally considered to be vegetatively propagated.

Technical 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.