Induced defence responses in Picea abies triggered by Heterobasidion annosum s.l

Sammanfattning: Norway spruce [Picea abies (L.)Karst.] is a key tree species for forest industry in Europe and stem and butt rot caused by Heterobasidion parviporum (Fr.) Niemelä & Korhonen is one of its major disease problems. The commercial gain using improved plant material could be even greater if resistance traits were included in the breeding program. The aim of this study was to increase the knowledge of the induced defences in response to H. annosum s.l. in Norway spruce bark. In this thesis it has been concluded that there is a significant variation between genotypes in a full-sib family of Norway spruce. The broad sense heritability was found to be 0.11 for fungal growth. A shift in the pathway connecting primary and secondary metabolism, as detected by a transcriptional switch of DAHP homologues, following H. annosum s.l. inoculation, indicate a possible allocation of more carbon to the secondary metabolism. We also found a consistent induction of the phenylpropanoid pathway and there was an association between the phenol profile and level of resistance. For example, the level of the flavonoid (+)-catechin showed temporal variation in genotypes with higher level of resistance. Matching changes was found in the transcriptome. The R2R3-transcription factor PaTT2-like gene, a putative regulator of flavonoid production, was found to be induced by jasmonic acid in bark. The responses to H. annosum s.l. have been shown to be non-specific but that the magnitude of the response is higher than with other types of challenges. A simultaneous up-regulation of genes related to the salicylic acid- and jasmonic acid-signalling pathway in response to fungal inoculation revealed a closer relationship between the pathways than has been observed in many angiosperms. Finally, the clonal variation in transcriptional and chemical responses observed in this thesis demonstrates variation between genotypes that can be related to different levels of susceptibility to H. annosum s.l. and which can be explored for improvement in coniferous trees. It also demonstrates some of the potential of using modern molecular methods in the breeding practices. Keywords: Picea abies, Heterobasidion, defence, transcript profiling, salicylic acid, jasmonic acid, phenylpropanoid pathway, flavonoids.

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