A TACF seed orchard represents one of the final generations of breeding in TACF’s current breeding program. It’s the next step for the offspring of resistant trees identified in the Chapter’s Backcross Breeding Orchards.
The Connecticut Chapter of the American Chestnut Foundation (CT-TACF) was established in 1995 and has worked with TACF’s breeding program for regional adaptability since 2005. During that time the Chapter has identified and incorporated over 20 different native American chestnuts from Connecticut into the breeding program and establishing several breeding orchards. The current breeding goals of CT-TACF include installing several seed orchards, where putatively blight-resistant Connecticut-bred chestnuts will be produced. CT-TACF is evaluating sites, and looking to identify partners that can assure long-term sites and support for these seed orchards.
The orchard should be installed on a chestnut-appropriate site, which is also relatively accessible to workers and volunteers. A seed orchard is a long-term project and should be expected to remain on the site for 30-45 years. In full operation six to eight years into its existence, a seed orchard would have twenty maturing if not yet fully grown American chestnut trees, that show signs of blight resistance, having acquired genes for resistance from both parents. They would have plenty of room to grow quickly as each would have about 40 feet square in which to spread. This was considered the optimal production spacing for Chinese chestnuts, where there is significant data on its use in orchards. Each of these chestnuts would have started out as a planting in a plot of some 150 trees (5 rows of 30 trees) with only one of them selected as the “best” example for breeding future generations. The seed orchard would have 20 plots, therefore the 20 trees remaining in the seed orchard after culling the 2980 that weren’t the “best” of their generation.
In the illustration of a seed orchard below, each letter represents a plot of 150 trees when initially planted. These trees come from one of the seven seed orchards located throughout Connecticut. The details of each plot are shown in Illustration 2 further down the page. Plots basically run up against each other and allow enough room between and alongside the fence to operate equipment. Eventually all but one of the trees in each plot are removed, and there remains plenty of room to operate, and for the remaining tree to grow stress-free and quickly, and produce significant quantities of fruit for reforestation purposes.
The TACF breeding program requires each state chapter to produce at least 20 distinct breeding lines within a given source of blight-resistance. These lines are produced by crossing advanced trees from the TACF Meadowview Research Farms with wild American chestnuts native to Connecticut. The resulting offspring are planted, grown to an appropriate size, and challenged with chestnut blight. Trees that exhibit the most blight-resistance and American chestnut character are selected for further breeding and the resulting nuts are then planted in a seed orchard.
A seed orchard planting will be at least one acre, which consists of one block. Each block of seed orchard contains 20 plots, each one representing a different American chestnut parent from CT. Within each plot, 150 trees are planted on tight spacing (Figure 2). With 20 of these plots, at least 3,000 nuts will be planted in a block over the duration of the planting phase of the orchard. Once all the trees in a given plot are about five years old, they will be challenged with the blight fungus. The best tree in each plot will be selected for breeding within the seed orchard, all others will be removed. This means that of the 3,000 nuts planted in a block, only 20 trees will remain after challenging with the blight fungus and making breeding selections. This process will take at least 10 years and, once completed, the orchard will be used for nut production to facilitate forest testing and reintroduction.
The main considerations for a seed orchard site are that the site is appropriate for growing American chestnut, accessible for equipment needed to install and maintain the orchard, secure for the expected duration of the planting and has a committed orchard manager with a plan for succession or changes in management.