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Goal: Sustain Our Nation’s Forests and Grasslands Mapping Phytophthora root rot resistance genes in American chestnut

Phytophthora root rot rating scale using the tub assay developed by James, Jeffers and Sisco. Class 2 and 3 indicate high susceptibility, class 1 moderate susceptibility, and class 0 resistance. This assay was used to phenotype the plants in the genetic mapping study.
Phytophthora root rot rating scale using the tub assay developed by James, Jeffers and Sisco. Class 2 and 3 indicate high susceptibility, class 1 moderate susceptibility, and class 0 resistance. This assay was used to phenotype the plants in the genetic mapping study. (Courtesy photo by Tatyana Zhebentyayeva, Steven Jeffers, and Paul Sisco, Clemson University)

Introduction

Phytophthora root rot is a serious disease of American chestnut that jeopardizes the success of chestnut restoration in the South. Using hybrid crosses and genomic techniques, SRS scientists mapped the major genes for resistance to Phytophthora cinnamomi, the microbe that causes this disease. The gene map is helping chestnut breeders and genetic engineers improve chestnut for planting on impacted sites.

Summary

Phytophthora cinnamomi, a soilborne oomycete, is a lethal pathogen of American chestnut (Castanea dentata). The microbe causes Phytophthora root rot (PRR) and is particularly damaging to chestnut and chinquapin in the southern U.S. Developing resistant genotypes is the most practical solution for disease management in forest trees such as Castanea.

Using backcross families derived from crosses of American chestnuts with two resistant Chinese chestnut genotypes (‘Mahogany’ and ‘Nanking’), the researchers genetically mapped quantitative trait loci for resistance to P. cinnamomi. In total, 957 plants representing five cohorts of three hybrid backcrosses were genotyped by sequencing and phenotyped using artificial inoculations.

The results imply that the genetic architecture of resistance to P. cinnamomi in Chinese × American chestnut hybrids resemble the P. sojae–soybean pathosystem and should allow chestnut breeders to efficiently produce resistant American chestnuts for restoration.

Principal Investigator
C. Dana Nelson, Project Leader
RWU
4160 - Forest Genetics and Ecosystems Biology
Strategic Program Area
Resource Management and Use
Publication
Dissecting resistance to Phytophthora cinnamomi in interspecific hybrid chestnut crosses using sequence-based genotyping and QTL mapping
Research Partners
Tatyana Zhebentyayeva, Penn State University
Steven N Jeffers, Clemson University
Margaret Staton, University of Tennessee
Albert Abbott, University of Kentucky
Barbara Crane, Regional Geneticist, Southern Region
External Partner
Jared Westbrook, The American Chestnut Foundation