In Vitro Responses of Conifer Adventitious Shoots and Calli Inoculated with Gremmeniella abietina

Abstract

Larix decidua adventitious shoots were inoculated with axenic vegetative hyphae and conidia of Gremmeniella abietina. Dense host surface mycelial growth and needle necrosis occurred after inoculation with vegetative hyphae and conidia within two weeks and four weeks, respectively. The pathogen completed its life cycle by producing pink conidial pustules on some infected propagules within one month. Light and scanning electron microscopic examination showed that hyphae penetrated commonly through or between epidermal cells and rarely through the stomates. Differential responses were evident within and between shoot clones. Inoculated calli of resistant L. leptolepis and Abies balsamea showed less mycelial growth than did L. decidua calli. Inoculation success was a function of spore inoculum density. In vitro responses correlated well with known in vivo responses. Our rapid (30-d) in vitro resolution of host resistance suggests that these methods may reduce the time required for evaluating relative disease resistance as compared to traditional field tests. For. Sci. 33(4):1047-1053.