Browsing by Author "De Jager, Muriel Mignon"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Assessment of the pathogenicity of fusarium euwallaceae to grapevine and deciduous fruit trees in South Africa and its rapid detection in woody tissues
    (Stellenbosch : Stellenbosch University, 2022-04) De Jager, Muriel Mignon; Roets, Francois; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: A myriad of different tree species in South Africa are under threat from the invasive woodboring beetle, Euwallacea fornicatus (Coleoptera: Curculionidae: Scolytinae), the polyphagous shot hole borer, PSHB. While constructing galleries in the wood of hosts these beetles release spores of a mutualistic fungus, Fusarium euwallaceae (Hypocreales; Nectriaceae).The fungus colonises the xylem tissues and acts as the primary food source for the beetle, but colonisation can lead to Fusarium dieback disease in susceptible hosts. Many economically important fruit tree species have been identified as possible hosts; however, no assessments have specifically tested the pathogenicity of F. euwallaceae towards these. The work presented in this thesis set out to evaluate the susceptibility of different deciduous fruit trees (plum, nectarine and apple) and grapevine to F. euwallaceae. The effect of branch diameter and increased inoculum load on the rate of lesion development was also assessed. Fusarium euwallaceae was pathogenic to all fruit tree species and cultivars tested but no evidence of disease development was recorded in grapevine. There were no significant differences in virulence between the different isolates. There was also no evidence that differences in branch diameter or differences in the number of inoculation points on a branch can affect the growth rate of F. euwallaceae. For monitoring, the presence of PSHB is often determined by positive identification of F. euwallaceae without collection of the beetle, particularly when beetles are not able to establish viable colonies. Standard approaches to identify F. euwallaceae are costly and labour- and time intensive as the fungus needs to be isolated and cultivated from freshly collected material, the DNA needs to be extracted and purified, and the DNA needs to be sequenced for a marker that can be used to identify it. In this thesis a faster, more accessible, and cheaper tool for the identification of F. euwallaceae in both fresh and dried wood samples which increases monitoring capacity when resources are limited is presented. A species-specific marker was identified from literature and an optimized PCR protocol for the identification of F. euwallaceae was developed that removes requirements to rear the fungus, purify its DNA and to sequence a DNA marker. This protocol was tested on eleven different hosts, all but one of which that produced positive results in at least one of the replicates. Amplification was not possible in one of the hosts likely due to the high concentration of PCR inhibitory compounds. In cases like this, a secondary measure based on the protocol developed here can be used where fungal isolates are first obtained from diseased woody tissues and these subjected to the rapid detection protocol. Amplification of F. euwallaceae DNA using this approach had a 100% reproducibility rate.