| description |
Identification of markers linked to traits of interest promises to be easier, more cost and time effective and more precise than traditional phenotypic selection in forest trees. Resistance to disease is a key trait of interest, and the Dothistroma – Pinus pathosystem provides an appropriate case study with which to pilot the development of a method to identify putative resistance to the disease, Dothistroma needle blight (DNB), whose primary causal agent is Dothistroma septosporum. To identify SNP markers linked to genes implicated in DNB resistance, transcriptome sequences from reliably phenotyped ‘resistant’ and ‘susceptible’ radiata pine trees from DNB-resistance trials in New Zealand were compared, and their likely transferability to Scots pine was tested. Due to financial and time constraints no attempt was made to test the utility of the SNPs within this project. Questions which were addressed in this study were: 1) Are there SNPs which are putatively associated with DNB-‘resistant’ phenotypes in radiata pine? 2) What is the degree of homology between radiata pine, Scots pine and loblolly pine? 3) How much of the transcriptome is putatively attributed to D. septosporum when trees are challenged with the pathogen and how does this vary with phenotype? A final set of 213 single nucleotide polymorphisms (SNPs) were found to be present in all ‘resistant’ individuals but in none of the ‘susceptible’ individuals. For 85 % of SNPs, homologs for their contigs (sequence surrounding the SNP) were found in a Scots pine reference transcriptome, suggesting that the majority of putative markers will amplify in Scots pine. Additionally, over 45 % of SNPs were found within genes which had a putative defence function (using gene ontologies from loblolly pine and Scots pine). The finding that ‘resistant’ phenotypes had lower levels of D. septosporum transcripts compared to ‘susceptible’ phenotypes indicates that mechanisms conferring low susceptibility to DNB may result in death, reduced proliferation or reduced gene activity of the pathogen within needles. The ultimate long term aim is to provide a set of molecular markers which can be used to diagnose DNB resistance in individual trees at an early stage of tree development, and which can be used in trees breeding and conservation. |