Abstract
BackgroundEucalyptus species, hybrids and clones are attacked byvarious fungal and bacterial pathogens and pests duringtheir life-time. Global climate changes are predicted tocreate favourable environments for such pathogens andpests and increase incidence of host jumping from othercrops, resulting in increased losses to the forestry indus-try [1]. The use of tolerant or resistant plant varieties aspart of an integrated disease management strategy isrecognised as a desirable means to curb disease inci-dence. Vertical resistanc e mediated by resistance ( R )genes, may be easily overcome by a pathogen and isthus not adequate on plantation species such as Euca-lyptus , which would be exposed to various pathogensduring its life-time. Broad spectrum resistance on theother hand, would be desirable to provide resistanceagainst multiple challenges [2].The aim of this study is to investigate mechanismsinvolved in host resistance with an emphasis on broad-spectrum resistance. The availability of the completegenome sequence of Eucalyptus grandis (http://www.eucagen.org) and the transcriptome sequence of aE. grandis X E. urophylla (GU) hybrid [3] has providedresources to investigate defense responses in the naturalhost. When a pathogen attacks a plant, the plantlaunches a sophisticated defense response involving phy-tohormones such as salicylic acid (SA), methyl jasmo-nate (MeJA) and ethylene (ET). These responses arefinely tuned and tailored to the invader [4]. Down-stream of the signalling cascade is the production ofpathogenesis related ( PR ) genes and antimicrobial geneswhich serve to limit the pathogen and afford protection.PR genes, such as PR-1 and PR-5, are known markers ofthe salicylic acid defense pathway, while PR-3 , PR-4 andthe lipoxygenase ( LOX ) genes are known markers of theMeJA and ET signalling pathways. The discovery of PRgenes in Eucalyptus is desirable as these genes have pre-viously been shown to afford broad spectrum resistancein other crops. We present our progress in exploitingthe Eucalyptus genomic and transcriptomic data for thediscovery of tree defense genes and explore the applica-tion thereof in determining which pathways areactivated in response to various pathogens.Materials and methods
Highlights
Eucalyptus species, hybrids and clones are attacked by various fungal and bacterial pathogens and pests during their life-time
We present our progress in exploiting the Eucalyptus genomic and transcriptomic data for the discovery of tree defense genes and explore the application thereof in determining which pathways are activated in response to various pathogens
Infections and infestations E. grandis clones were treated with Chrysoporthe austroafricana in the following manner: wounds were created using a 0.3cm cork borer to expose the cambial tissue and an agar plug containing fungal mycelia were applied to the wound and sealed with parafilm
Summary
Eucalyptus species, hybrids and clones are attacked by various fungal and bacterial pathogens and pests during their life-time. Vertical resistance mediated by resistance (R) genes, may be overcome by a pathogen and is not adequate on plantation species such as Eucalyptus, which would be exposed to various pathogens during its life-time. Eucagen.org) and the transcriptome sequence of a E. grandis X E. urophylla (GU) hybrid [3] has provided resources to investigate defense responses in the natural host. When a pathogen attacks a plant, the plant launches a sophisticated defense response involving phytohormones such as salicylic acid (SA), methyl jasmonate (MeJA) and ethylene (ET). These responses are finely tuned and tailored to the invader [4]. Downstream of the signalling cascade is the production of pathogenesis related (PR) genes and antimicrobial genes which serve to limit the pathogen and afford protection
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