Genetic variation in susceptibility to Phytophthora Cambivora in European chestnut (Castanea sativa)

Genetic variation in 23 populations of European chestnut (Castanea sativa L) to Ink Disease caused by Phytophthora cambivora (Petri) Buisman was studied in three labs. The populations represented three domestication levels (naturalized populations, coppice forests and orchards) and were sampled in 10 locations in five countries (Italy, France, Greece, Spain, and the UK). Adult chestnut susceptibility to Ink Disease was assessed by measuring lesion length following inoculation of excised shoots with P. cambivora. Half-sib families were harvested in most of these populations and the seedlings were root-inoculated. Provenance and family variance components were estimated. Significant variation in the extent of shoot colonization by P. cambivora was observed within and among adult tree populations, suggesting a large amount of genetic variation in resistance. No consistent ranking of the domestication levels for susceptibility was observed. Some results indicate selective pressure exerted by P. cambivora on local populations. Lesion measurements in a set of 48 trees inoculated in 2001 and 2002 were correlated (r = 0.58). One or more resistant trees (lesion length <10 mm) were identified in 15 populations. Root inoculation of seedlings showed that only three families had a mean value for percentage of infected taproot = 15% or comparable to seedlings of the resistant control ‘Marigoule’. Lesion lengths in parent trees and percentage of infection of the taproot of their seedlings were not highly correlated.