Natural infection of stumps and stump roots in Douglas-fir by Heterobasidion after thinning | Mise en évidence de l'infection naturelle des souches et des racines de Douglas par le Fomes après éclaircie

French. Un jeune peuplement de Douglas ayant subi une première éclaircie en octobre 1997, et jouxtant une importante source d'inoculum naturel, a fourni une opportunité particulièrement intéressante pour étudier l'infection des souches. Un peuplement voisin de sapins de Vancouver (Abien grandis), atteint sévèrement par H. annosum et producteur de nombreux carpophores parfois de grande taille, constituait une source importante d'innoculum aérien naturel susceptible de contaminer la surface fraîche des souches de Douglas voisins, qui se sont donc trouvées dans une situation de fort risque d'infection au moment de l'éclaircie. L'étude a été menée entre 1999 et 2001. On donne les résultats pour ces années.

English. Heterobasidion was investigated in 50 stumps 20 months after the first thinning in a 17 y.o. Douglas-fir stand planted after the harvest of an unthinned Norway spruce stand. Next the plot was a grand fir plantation severely infected by Heterobasidion with sporophores abundantly present on stumps. No discoloration or decay were present but 19 stumps were infected (38 %). Heterobasidion sp. was present only in sapwood. 45 roots (20-120 cm long) were collected from 9 infected stumps, and 32 roots (70-270 cm) from 8 "uninfected" stumps. 41 roots were infected in the infected stumps, and 2 in one "uninfected" stump. In general, roots were in general entirely colonised ; partial colonisation was always located next to the stump. Results suggest that infection was primarily carried by airborne basidiospores to fresh stumps and infection originating from roots could not be demonstrated. Isolates of Heterobasidion were obtained from sporophores on grandfir and on douglas-fir in an another plantation some hundreds of meters apart and collected from stumps and roots. All the sporophores were H. abietinum. H. abietinum (F) (2/3) and H. annosum stricto sensu (P) (1/3) were detected in the stumps and roots. Roots were also extensively colonised by Armillaria ( A. gallica and A. mellea).