Restoration of American chestnut: A marriage of breeding and - - PowerPoint PPT Presentation
Restoration of American chestnut: A marriage of breeding and biotechnology Jared Westbrook The American Chestnut Foundation National Academy of Science Forest Health Webinar December 12, 2017 Early breeding programs to introduce blight
Restoration of American chestnut: A marriage of breeding and biotechnology
Jared Westbrook
The American Chestnut Foundation National Academy of Science Forest Health Webinar December 12, 2017
Chinese chestnut
Early breeding programs to introduce blight resistance from Asian Castanea
American chestnut
¡ ¡
F1 ¡
Intermediate blight resistance, not competitive in the forest
Three generations of backcrossing to recover American chestnut form Two generations of intercrossing to enhance blight resistance
The American Chestnut Foundation’s Backcross breeding program
Charles ¡Burnham ¡
Sources of resistance and backcross lines
¡ ¡ Graves Clapper ‘Clapper’ and ‘Graves’ are BC1 trees from early breeding programs have been bred as distinct sources of resistance 20 BC2 x 20 Americans
Fred Hebard TACF Emeritus
BC1 x 20 Americans
TACF’s chapters breed backcross hybrids with American chestnuts throughout the range ¡
1 of 64 of the BC3F2 progeny expected to inherit 3 genes for blight resistance from both parents ¡
Backcross trees intercrossed to enhance blight resistance
X =
BC3 BC3 BC3F2
Selection against blight susceptibility in seed orchards
Artificially inoculate stems at age two with C. parasitica ¡
Clapper Graves N (%) trees planted 36,000 (100%) 25,000 (85%) N trees remaining 3297 2244
Progress of selection in seed orchards at TACF’s Meadowview Research Farms
Progeny testing to make final selections for blight resistance after initial culling
Partially selected seed orchard Unselected BC3F2 seed orchard Open-pollination among BC3F2 survivors Artificially inoculate BC3F3 progeny from each selection candidate
Average canker severity
Ar0ficially ¡inoculate ¡ & ¡cull ¡suscep0ble ¡ ¡
Progeny testing is too slow to finish selection for blight resistance
¡ ¡ Clapper Graves Number BC3F2 trees remaining 3200 2200 N BC3F2 parents progeny tested 2009-2017 300 300 N BC3F2 to select 300 300 N trees remaining after selection based on canker size >> N trees progeny tested Meadowview breeding program
Development/validation of genomic prediction models for disease resistance
9/10th of training population
Canker size/root rot severity
=
+
+0.5 +0.9 Estimated marker effects Genome-wide markers Experimental design
+0.5 +0.9 Marker genotypes
x
i = 1
N markers
=
Predicted pathogen resistance Marker effects
µ + Χβ
1/10th of training population Repeat 10 x Accuracy = correlation
Proof-of-concept
Genomic prediction of blight resistance of BC3F3 progeny Response ¡variable: ¡BLUPs ¡es0mated ¡from ¡canker ¡ra0ng ¡and ¡canker ¡ lengths ¡of ¡11 ¡– ¡30 ¡open ¡pollinated ¡progeny ¡of ¡each ¡BC3-‑F2 ¡mother ¡
Weak strain Strong strain N individuals = 47 BC3F2 N SNPs = 22,397
Intermediate blight resistance expected after selection is complete in seed orchards
Dashed line prediction of average canker severity of BC3-F3s after selection is complete in BC3-F2 seed orchards Scale 100 = American chestnut average 0 = Chinese chestnut average
American chestnut BC3F2 trees with improved blight resistance
BC3F2 tree American chestnut
Incorporating transgenic blight resistance into TACF’s breeding program
~50% of offspring inherit the oxalate detoxifying gene
Transgenic pollen Pollinate wild-type mother trees Harvest nuts and test for inheritance of OxO Bill Powell SUNY-ESF Chuck Maynard SUNY-ESF
Transgenic outcross simulation: N generations & N American parents/generation
N outcross generations N American parents per generation Ne 2nd Intercross
intercross 2 2, 1000 154 0.08 2 500, 500 297 0.03 3 2, 500, 500 190 0.02 3 500, 500, 500 530 0.009 4 250, 250, 250, 250 736 0.004
Effective pop. size (Ne) greater and inbreeding (F) less with:
Outcrossing transgenic founder to diversify, minimize inbreeding, and stack resistance
Transgenic American chestnut
x 500 American chestnuts per generation 3 generations of outcrossing to dilute the founder genome Intercross to generate large quantities of seed for restoration
Nanking Graves Clapper Backcross + OxO resistance stacking Outcross to 200 backcross selections/ generation x 3 generations, 1 resistance source/generation Create diverse pure American lines Outcross to 300 Americans/generation x 3 generations
American chestnut genetic diversity conservation
Collecting pollen and seed from rare flowering wild trees Transplanting the wild trees and conserving the trees in orchards
Objective: 2500 new sources of American chestnut planted in germplasm conservation orchards by 2020
Phytophthora root rot caused by soil-borne pathogen Phytophthora cinnamomi Imported to N. America from S.E. Asia in 1800’s The North American and European Castanea species are susceptible, while the Asian species are resistant
Chestnut blight is not the only impediment to American chestnut restoration ¡
Range of Phytophthora cinnamomi predicted to expand northward as climate warms
Range of P. cinnamomi as of 1945 (Crandall et al. 1945) Predicted range of P. cinnamomi by 2080 (Burgess et al. 2017)
Screening backcross populations for resistance to Phytophthora cinnamomi
Photos by S.N. Jeffers
Artificial inoculation with P. cinnamomi Severity ¡ra0ng ¡of ¡root ¡lesions ¡ Measurement of above ground wilting and mortality
Some Graves families have high levels of root rot resistance
10 20 30 40 50 60 70 80 90 100
American chestnut Clapper B3−F2s Graves B3−F2s Chinese chestnut
Scaled breeding values PRR resistance
Resistance to chestnut blight and Phytophthora root rot uncorrelated
−0.5 −0.4 −0.3 −0.2 −0.1 0.0 0.1 0.2 0.3 −2.00 −1.75 −1.50 −1.25 −1.00 −0.75 −0.50 −0.25 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 Blight canker severity BLUPs PRR mortality BLUPs
Additional breeding required to combine blight and PRR resistance
Blight resistant transgenic
PRR resistant BC3-F2 selections Select for PRR resistance and deploy
2 generations of breeding and selection
Intercross to increase PRR resistance
X X X
Restoration of American chestnut depends on:
trees can reproduce in native range
Phytophthora resistance in southern forests
diversity to adapt to a changing world
Questions? www.acf.org
Predicted distribution of suitable habitat in 2080 (lower greenhouse gas emission scenario) Current distribution of suitable habitat
The future: distribution of suitable habitat expected to shift North with climate change
Predicted distribution of suitable habitat in 2080 (higher greenhouse gas emission scenario) Jessica Cavin Barnes NCSU