American Chestnut (Castanea dentata) - A Great American Tree ...

American Chestnut (Castanea dentata) - A Great American TreeRobert Strasser – Hood College

Americanchestnut leavesturn goldenbrown inAutumn.

Chestnut flowering in early summer in the Blue Ridge.

The Appalachian mountains are the coreof the species’ natural range.

Domain – EukaryaKingdom – PlantaePhylum – AnthophytaClass – DicotyledonesOrder – FagalesFamily – FagaceaeGenus – CastaneaSpecies - dentataFungiEubacteriaPlantaeAnimaliaPro tistaArchaebacteriaHow chestnutfits amongliving things:Origins of Life > 3.5 BYA

Beech family (Fagaceae) : Beech (Fagus) and Oak(Quercus) and Chestnut (Castanea)1. Chinese – Castanea mollissima2. Japanese – Castanea crenata3. European – Castanea sativa4. American – Castanea dentata• Four other Castanea species – chinquapins in North America• Many can hybridizeChestnut Classification

Evolutionary Migration Pathway – Castanea•Chloroplast DNA sequences suggest a common Castanea ancestor originatedin Laurasia about 40 – 60 million years ago. C. dentata probably diverged from C.sativa in the late Eocene epoch – approximately 35 million years ago.

Leaf Identification (L to R): American Chestnut (C. dentata), ChineseChestnut (C. mollissima), Chinkapin (C. pumila), European Chestnut (C.sativa), and Japanese Chestnut (C. crenata).

Twigs and Buds,Left – Right:AmericanChineseEuropeanJapanese

Chestnuts (Left – Right): American, Chinese, Japanese, European

Chestnuts make nice shade trees.

American chestnutswere abundant andcould reach very largesizes.

Chestnut was a versatile hardwood quite valuable to rural American life.

American Chestnut‟sDiverse Uses:•Fencing•Telegraph poles•Railroad ties•Shingles and siding•Framing lumber•Furniture•Heavy timber contstruction•Tanin production•Charcoal•Fuel•Food

AbrahamLincoln“Fence Splitter”

Approximately 600,000,000board feet of chestnut lumberwas cut in 1909, bringingabout $10,000,000 to theeconomy of Appalachia.Chestnut wood harvests inthe US peaked between1907 and 1910.

Many good foods can be made with chestnuts.

Wildlife thrived on American chestnuts.

Late 1800’s -Blight PandemicBegan• Parasitic fungus - Cryphonectria parasitica• Enters bark and infects cambium, not roots• Rapid, uncontrollable dispersal

An estimated 3-4 billion American chestnuts grew at beginningof the blight pandemic, and most died within 50 years.

Ridges dominated by chestnut were devastated.

Spread ofCryponectriaparasitica

Biology of Cryphonectria parasitica :• Infections are perennial• Reproduce asexually and sexually via spores• at least 64 different strains

Point ofEntrySwellingCankerSunken Canker

Blight infects trees of all ages and sizes, not always killing them quickly.6 Months ~ 6 Years > 20 years

Chestnut survives by growing slowly in the shade.

ForestUnderstoryShenandoahNational Park

Surviving C. dentataRolling RidgeFoundationHarper‟s Ferry, WV

LaMonica TreeMarshal, VirginiaJanuary 2008

Jim Hill‟s Tree (#6546)Height 85 feetDiameter 13 inchesMt. Airy, Maryland

Evil Tendendencies CancelWill the blight end the chestnut?The farmers rather guess not.It keeps smoldering at the rootsAnd sending up new shoots.„Till another parasiteShall come and end the blight.-Robert Frost (1936)

Uninfected BarkIs this resistanceor hypovirulence?Non-leathal Canker

Hypovirus in vitro – Blight Strain EP155Hypervirulentno virusHypovirulentvirulent virusHypovirulentweak virus

Anastomosis:fusion of fungalhyphae• Cytoplasmic exchange between individuals• Viral RNA can transmit hypovirulence between strains

Compatible blight strains:• Anastomosis possible• Viral transmission possibleIncompatible blight strains:• No anastomosis• No viral transmission

The American Chestnut Foundation – Founded 1983Beginning in 1987, TACF initiated a systematic program toincorporate blight resistance found in Asian chestnuts into theAmerican chestnut through backcross breeding.

Chinesechestnut resistsblight, but issmaller instature.

Americanchestnutgrows tall andstraight…butis susceptibleto blight.

TACF‟s BackcrossBreeding ProgramChineseXAmericanEach generation select for: Blight resistance American characteristicsF 1 ½ American (50%)BC 1 ¾ American (75%)XXAmericanAmericanFinal Product: goal is truebreedingAmerican typewith a high levelof blight resistanceBC 2 7 / 8 American (88%)BC 3 15 / 16 American (94%)XXAmericanBC 3BC 3 F 2 15 / 16 American (94%)XBC 3 F 2BC 3 F 3 15 / 16 American (94%)

RR x rr = Rr (F 1 )Rr x rr = Rr and rr (BC 1 )Rr x rr = Rr and rr (BC 2 )Rr x rr = Rr and rr (BC 3 )Rr x Rr = RR, Rr and rr (BC 3 F 1 )RR x RR = RR (BC 3 F 2 )RR x RR = RR (BC 3 F 3 )Proposed genetics of blight resistance:R = Resistance factor (Chinese)r = recessive allele (American)

Dr. Hill Craddock with an intercross chestnut near Chattanooga, TN.

What are we looking for in ourbackcross chestnuts?• Blight and other disease resistance• American phenotype• Genetic diversity

Pollination inthe field ofteninvolves theuse of bigladders andbucket trucks.

Controlled PollinationChestnuts are amonoecious species:They have both maleand female flowers onall trees.

Staminate Catkins – Male Flowers Only

Bisexual Catkins – Both Female and Male Flowers

Trimming catkinsto leave onlyimmature femaleflowers.

Receptive flowers arefertilized with dried pollenfrom selected father trees.

Pink ribbons mark unpollinated check (control) bags.

Burs become heavy in late summer.

Late September – Burs Open

Left: pollinated bur.Right: Un-pollinated bur.

Screening Chestnuts for BlightResistance: Paired Inoculations1. Trees are infected with two strains of blight:• EP 155 – highly virulent• SG 2 3 – moderately virulent2. Cankers evaluated after 12 months• Large cankers – poor resistance• Small cankers – better resistance

Resistance: ability to limit the spread of disease.Immune --- Resistant ---SusceptibleBlight resistance in chestnut is ranked numerically:1 - - - - - 2 - - - - - 3 - - - - - 4 - - - - - 5Strong - - - Good - - - Moderate - - - Poor - - - None

Inoculation of3 Year OldChestnutsWith Blight2) Insert cultures1) Bore hole in cambium3) Seal with tape

Paired Inoculations1 year post-inoculationResistance Rating: 5Castanea dentataSG 2 3EP 155EP 155

ThorpeWood Tree 50 – Backcross 1Inoculated June 2004 - Resistance Rating: 2.5SG 2 3SG 2 3EP 155EP 155June 2005 June 2006Jan 2008

…but trees withenough blight resistanceare advanced bybreeding them again.Blight susceptible treesare cut down…

How can you get involved?• Join the American Chestnut Foundation• Help plant, pollinate, and care for trees• Pursue research to advance science

www.acf.orgwww.vatacf.org