Defining Pollen FLOW PATTERNS IN A BLACK Walnut (JUGLANS NIRA L.) ORCHARD IN Missouri

A paternity analysis was conducted to increase our understanding of spatial pollen flow dynamics within black walnut orchards.  Open pollinated seeds were collected from three 10 year old ramets of the cultivar, ‘Sparrow’, growing in a clonal repository in central Missouri.  This study orchard contained a total of 21 cultivars, each represented by two to four ramets.  A total of 389 nuts derived from the 2006 seed year were genotyped using 11 microsatellite markers and compared to the genetic fingerprints of all potential pollen sources within the orchard to determine paternity.  In addition, 191 wild trees growing within a radius of 500m of the study orchard were genotyped using 11 microsatellite markers to provide an estimate of potential pollen contamination.  The number of pollen donors varied by ramet, and no dominant pollen source was identified.  Rather, each ramet was associated with a different dominant pollen parent.  Observed selfing rates ranged from 2.7 to 3.9 percent.  Pollen contamination ranged from 45.7 to 59.3 percent, depending upon ramet.  Spatially, the majority of contamination came from >500m, since only 6.0 to 14.9 percent of this outside pollen could be sourced to the 191 wild trees growing within 500m of the study orchard.