The American Chestnut Foundation (TACF) has been working for over four decades to improve the disease resistance of American chestnut seedlings to be reintroduced into our forests. The focus of the foundation’s current efforts is to utilize Recurrent Genomic Selection (RGS) to increase disease resistance and increase the genetic diversity of resistant seedlings. One way that the VT/NH Chapter of TACF is helping with the RGS efforts is to establish and maintain Progeny Test plantings and Seed Orchards that are comprised of seedlings that are genotyped (laboratory assessments of specific genes) to determine that they contain genes associated with increased disease resistance. Following blight inoculations, the seedlings are also examined in the plantings to measure their Blight Resistance Index. This index measures blight resistance on a scale of 0-100 with above average blight resistance being greater than 50 on the index scale.
An important part of this effort is to conduct controlled pollinations of selected parent trees to create RGS offspring to be included in the Progeny Test and Seed Orchards. After TACF has evaluated male and female parent trees that are above average in disease resistance and contain genes associated with disease resistance, the next step is to conduct controlled pollinations among these trees to potentially increase disease resistance in the resulting offspring. These offspring will be planted in the Progeny Tests and/or Seed orchards.
Conducting controlled pollinations is generally a three-step process: (1) bag the female flowers to prevent pollen contamination; (2) pollinate the female flowers with selected pollen; and (3) harvest the mature chestnut burs that contain the control pollinated nuts. All three of these steps must be conducted at critical stages in the flower development process. In addition, to be sure that no foreign pollen contaminates the process, bagged, but unpollinated, control bags are included that should not contain viable nuts. TACF and the Manton Foundation have produced an excellent document explaining American chestnut floral biology and controlled pollination procedures that can be found here: American Chestnut flowers and breeding.
The VT/NH TACF chapter conduced controlled pollinations of a selected tree that has been growing in a B3F3 plantation on the Growold Estate in Shelburne Vermont. This mother tree was genotyped and contained 89.2% American chestnut genes and was rated 43.6 on the Blight Resistance Index. On June 30th, this tree was bagged with a total of 104 separate bags including 9 control bags and was completed by Gary Hawley (VT/NH TACF Vice President) and Paula Murakami (US Forest Service Ecologist) using an electric lift unit. The bagged female flowers were later pollinated with two separate pollen sources on July 8th. These pollinations were conducted by Deni Ranguelova (TACF Regional Science Coordinator), a TACF summer intern and Gary Hawley. Fifty of the bags were pollinated using pollen from a selected male parent from Shieling Forest, NH and the remaining 43 bags were pollinated by pollen from another tree in the RGS program from the New England region. We expect to harvest the control-pollinated nuts in early October.
Written by Gary Hawley
