Phytophthora cinnamomi Rands, the causal pathogen of phytophthora root rot (PRR) of chestnut, is one of the main obstacles to growth of american chestnut [Castanea dentata (Marsh.) Bork.] in the southern part of its distribution. To facilitate introgression of PRR resistance of chinese chestnut (C. mollissima Blume) into a C. dentata genetic background, we assessed the disease resistance of 10 interspecific hybrid families derived from potentially resistant C. mollissima cultivars. Hybrid progeny were inoculated with P. cinnamomi in the nursery and assessed for root lesion severity after 1 year of growth. Asymptomatic plants were transplanted to a P. cinnamomi-positive orchard and evaluated for survival midway through the following growing season. During the nursery experiment, 8 of 10 hybrid families were not significantly different from susceptible C. dentata controls for average disease resistance scores. However, multiple asymptomatic individuals were identified in each of the eight families. Two of the 10 hybrid families were not significantly different from the resistant C. mollissima and C. henryi controls. In the P. cinnamomi-positive orchard, the prescreened hybrid families displayed a greater proportion of survivors than backcross families that had not been prescreened for P. cinnamomi resistance. Hybrid plants that have survived 2 years of growth in P. cinnamomi-infested potting media and soils represent an important step toward the production of genetically diverse chestnut populations in the southeastern United States that combine the PRR resistance of C. mollissima with the morphology and local adaptation of C. dentata.
This work was supported by a grant from the American Chestnut Foundation and a University of Tennessee at Chattanooga Provost Student Research Award to M. Taylor Perkins. We acknowledge additional support from the Summerfield Johnston Endowment for the Restoration of the American Chestnut, and the Bettie J. Smith FLP.
We thank those who shared their time and expertise for this project: Paul H. Sisco for guidance regarding the “better backcross” and aspects of experimental design; Tatyana N. Zhebentyayeva for guidance regarding experimental design; Paola Zannini for breeding database management and assisting with implementation of the experiments and data collection; David Morris, Jack Agricola, and members of the Alabama Chapter of the American Chestnut Foundation for providing pollen and for assisting in the greenhouse; Clint Neel for providing pollen and seeds; and Thomas M. Saielli of the American Chestnut Foundation for providing American chestnut seeds. Special thanks are given to Steven N. Jeffers and Suzette Sharpe for providing guidance and resources for Phytophthora isolation, species identification, and design of disease resistance screening experiments. We thank Lisa W. Alexander and Jared W. Westbrook for reviewing the manuscript.
JeffersS.N.2015Protocol 07-11.1: V8 agar (V8A) or broth. In: K. Ivors (ed.). Laboratory protocols for Phytophthora species. 1 Mar. 2015. <https://www.apsnet.org/apsstore/Pages/protocolsTOCdes.aspx>
JeffersS.N.JamesJ.B.SiscoP.H.2009Screening for resistance to Phytophthora cinnamomi in hybrid seedlings of American chestnut. Proc. Fourth Meeting of the International Union of Forest Research Organization (IUFRO) Working Party S07.02.09: Phytophthoras in Forests and Natural Ecosystems. E.M. Goheen and S.J. Frankel (tech. coords.). Gen. Tech. Rep. PSW-GTR-221. USDA Forest Service Pacific Southwest Research Station Albany CA. p. 188–194
JeffersS.N.MeadowsI.M.JamesJ.B.SiscoP.H.2012Resistance to Phytophthora cinnamomi among seedlings from backcross families of hybrid American chestnut. Proc. Fourth International Workshop on the Genetics of Host-Parasite Interactions in Forestry: Disease and Insect Resistance in Forest Trees. R.A. Sniezko A.D. Yanchuk J.T. Kliejunas K.M. Palmieri J.M. Alexander and S.J. Frankel (tech. coords.). Gen. Tech. Rep. PSW-GTR-240. USDA Forest Service Pacific Southwest Research Station Albany CA. p. 194–195
MetaxasA.M.2013Chestnut (Castanea spp.) cultivar evaluation for commercial chestnut production in Hamilton County Tennessee. Univ. of Tennessee Chattanooga TN MS thesis
PailletF.L.1993Growth form and life histories of American chestnut and Allegheny and Ozark chinquapin at various North American sitesBull. Torrey Bot. Club1203257268
Paillet,F.L.1993Growth form and life histories of American chestnut and Allegheny and Ozark chinquapin at various North American sites1203257268)| false
SiscoP.H.2009Outlook for blight-resistant American chestnut trees. National Proceedings: Forest and Conservation Nursery Associations—2008. R.K. Dumroese and L.E. Riley (tech. coords.) Proc. RMRS-P-58. USDA Forest Service Rocky Mountain Research Station Fort Collins CO. p. 61–68
SteinerK.C.WestbrookJ.W.HebardF.V.GeorgiL.L.PowellW.A.FitzsimmonsS.F.2017Rescue of American chestnut with extraspecific genes following its destruction by a naturalized pathogenNew For.482317336
Steiner,K.C.Westbrook,J.W.Hebard,F.V.Georgi,L.L.Powell,W.A.Fitzsimmons,S.F.2017Rescue of American chestnut with extraspecific genes following its destruction by a naturalized pathogen482317336)| false
ZhebentyayevaT.StatonM.OlukoluB.ChandraA.JeffersS.JamesJ.SiscoP.HebardF.GeorgiL.NelsonC.D.AbbottA.G.2014Genetic and genomic resources for mapping resistance to root rot disease (Phytophthora cinnamomi) in chestnutActa Hort.1019263270
Zhebentyayeva,T.Staton,M.Olukolu,B.Chandra,A.Jeffers,S.James,J.Sisco,P.Hebard,F.Georgi,L.Nelson,C.D.Abbott,A.G.2014Genetic and genomic resources for mapping resistance to root rot disease (Phytophthora cinnamomi) in chestnut1019263270)| false