The American chestnut, Castanea dentata, was once one of the most dominant trees in the forests of the Eastern United States until a pathogenic fungus, Cryphonectria parasitica, was introduced from Asia around 1900. By 1950 the blight had spread throughout the tree’s entire range, effectively extirpating the species from North America.

Seed Germination, Seedling Establishment, and Sapling Growth of Blight-Resistant American Chestnut (Castanea dentata) in a Progeny Test Orchard

Kristen Vigneau (Biology ‘15) and Eric Berry, Ph.D.Department of Biology, Saint Anselm College, Manchester, NH, USA

Background and Objectives

Methods

We would like to thank the Beaver Brook Association as well as The American Chestnut Foundation for access to their progeny test orchard. Funding was provided by the Saint Anselm College Biology Department.

Acknowledgments

In an effort to restore the American chestnut to its native range, The American Chestnut Foundation (TACF) has been working for decades to breed a blight-resistant tree. TACF has crossed American chestnut trees with a Chinese chestnut species, Castanea mollissima, which carries genes for blight resistance. The hybrid offspring of this cross has been backcrossed with American chestnuts for several generations to create a hybrid that is phenotypically and ecologically similar to the American, but retains the blight-resistance of the Chinese (Figure 1, from TACF educational literature).

To test the performance of the final backcrosses, the BC3F3, TACF planted a progeny test orchard in Hollis, NH in 2012. To facilitate comparison with the BC3F3, the orchard includes pure American and Chinese chestnuts, and an earlier generation of hybrid, the BC3F2.

Research Objectives:Examine and compare seed germination, seedling establishment, and sapling growth among the different species and hybrids within the test orchard.

Figure 2. Top - Photograph of progeny test orchard site

Bottom - Diagram of planting map based on randomized block design

Right – Diagram key

Figure 3. Percentage germination and establishment. Asterisks (*) indicated statistically significant differences from the BC3F3

based on Χ2 tests (α = 0.017).

D1-28-24 D4-28-13 D4-9-105 D5-26-54 W2-32-100

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Pictured right: 3-year old BC3F3

Results

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Seed Germination and Seedling Establishment• Emergence of Chinese seedlings was significantly lower than

other trees (Figure 3)• Two seed sources for American (Raystown, PA v. Canaan, NH)

were not significantly different

• Two seed sources for BC3F3s (Clapper v. Graves) were not significantly different

• No significant block effect on seedling emergence

Seedling and Sapling Growth• American seedlings grew least in 2012, but all trees grew equally in 2013 (Figure 4 top)• No difference between tree types in 2013 total height, but Chinese trees grew less than others in 2014 (Figure 5 top)• Seedlings from the Graves line (W2-32-10) grew significantly less in 2012, 2013, and 2014 than seedlings from the

four Clapper lines (Figure 4 bottom, Figure 5 bottom)

Conclusions

Figure 4. Comparison of 2012 seedling height (brown, upper-case letters) and 2013 growth (green, lower-case letters) between four different tree types (top) and between five BC3F3 hybrids (bottom). Different letters indicate significant differences (P<0.05) from blocked ANOVA.

Figure 5. Comparison of 2013 seedling height (brown, upper-case letters) and 2014 growth (green, lower-case letters) between four different tree types (top) and between five BC3F3 hybrids (bottom). Different letters indicate significant differences (P<0.05) from blocked ANOVA.

Seedling Growth Sapling Growth

Field Sampling• Site: Beaver Brook Association, Hollis, NH• Data collection dates: Germination (08/23/12) and

Height (3/29/13, 4/21/14, 10/10/14)• Method: Annual height measured to the nearest inch.

Leaf phenology recorded at intervals each spring (data not presented here).

• Randomized complete block design (Figure 2): 25 blocks each containing two American nuts, two Chinese nuts, two BC3F2s, and ten BC3F3s.

• Blocked ANOVA: Differences between tree types were tested for statistical significance using a blocked ANOVA, which allows the impact of uncontrolled environmental variation between blocks to be subtracted from the main effects (tree type).

• BC3F3 nuts contain blight resistance from two main lineages as displayed by cross codes: D were retrieved from the Duncan farm and descended from Clapper (BC1) whereas W are from the Wagner farm and are descendants of Graves (BC1).

• American and both hybrid chestnut seeds germinated and established very well in the test orchard.

• After three years growth, both chestnut hybrids had established and grown as well as the American trees.

• By the end of 2014 growing season, the shorter Chinese tree growth form was becoming apparent.

• All three years growth data indicate that hybrid trees from the Graves line performed much more poorly than those from the Clapper lines.