An investigation on the response of living conifer tissues to saprotrophic Phlebiopsis gigantea and its potential to acquire necrotrophic capability. study1

The saprotrophic fungus P. gigantea has been used for several years as a biocontrol agent against the conifer pathogen (Heterobasidon annosum). Although, the effectiveness of P. gigantea in biocontrol has empirically been shown, the long-term effect on living conifer trees as well as mechanism for its antagonistic activity is still unknown. Additional concern is the potential of P. gigantea to acquire necrotrophic habit through adaptation to living wood tissues. Using a combination of histochemical, molecular and transcript profiling (454 sequencing), we investigated under in vitro conditions necrotrophic capability and induced localized resistance as a mechanisms for its biocontrol action. Conifer tree seedlings (8-10 year old) were challenged to the xylem surface with P. gigantea or H. annosum. Both fungi provoked strong necrotic lesions, but at prolonged incubation time, P. gigantea lesions shrunk accompanied with cell regeneration. Tree seedlings pre-treated with P. gigantea restricted further H. annosum induced necrosis and had more lignified cells. The 454 sequencing revealed elevated transcript levels of genes important for lignification, cell death regulation and jasmonic acid signalling. The results suggest that induced localized resistance is a contributory factor for its biocontrol efficacy and P.gigantea comparatively has limited ability to acquire necrotrophic habit.