Differential resistance of gordonieae trees to phytophthora cinnamomi

Abstract

Trees in the Theaceae tribe Gordonieae are valuable nursery crops, but some ofthese taxa are known to be highly susceptible to root rot caused by Phytophthoracinnamomi Rands. The objective of this study was to evaluate a collection of Gordonieaetaxa for resistance to this pathogen. These taxa included Franklinia alatamaha Bart. Ex Marshall, Gordonia lasianthus (L.) Ellis, Schima wallichii Choisy, S. khasiana Dyer,×Schimlinia floribunda Ranney & Fantz, and ×Gordlinia grandiflora Ranney & Fantz.Abies fraseri (Pursh) Poir. was also included in the study as a positive control. Containergrowntrees were inoculated with three isolates of P. cinnamomi and symptoms wererated over an 84-day period during the summer of 2008. Disease symptom ratings from 1(healthy) to 4 (dead) were collected twice weekly and area under the disease progresscurve (AUDPC) values were calculated. None of the S. khasiana or S. wallichii exhibitedany root rot symptoms or mortality, whereas the remaining species showed symptoms ofinfection at varying levels over time. Symptoms in F. alatamaha and A. fraseri wereapparent before other taxa, and mortality for both species reached 100% by the end ofthe experiment. Comparison of AUDPC values indicated that F. alatamaha was the mostsusceptible followed by A. fraseri. There was no significant difference in AUDPC amongthe more resistant taxa, including G. lasianthus, both Schima species, and the intergenerichybrids. Values for AUDPC in the hybrid taxa were similar to their more resistantparental genus, indicating that resistance to P. cinnamomi is a partially dominant trait inthese plants. These results further suggest the potential to breed improved hybrids ofGordonieae trees with substantial resistance to P. cinnamomi.