The impact of the polyphagous shot hole borer beetle and its fungal symbiont, Fusarium euwallaceae, on commercial pear production
| dc.contributor.advisor | Crous, Casparus J | en_ZA |
| dc.contributor.advisor | Roets, Francois | en_ZA |
| dc.contributor.author | Neethling, Emma Cecile | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology. | en_ZA |
| dc.date.accessioned | 2025-04-03T10:31:04Z | |
| dc.date.available | 2025-04-03T10:31:04Z | |
| dc.date.issued | 2024-12 | |
| dc.description | Thesis (MAgric)--Stellenbosch University, 2024. | en_ZA |
| dc.description.abstract | This thesis investigates the impact of the invasive polyphagous shot hole borer (PSHB) beetle and its fungal symbiont Fusarium euwallaceae (FE) (together PSHB-FE) on commercial pear production, specifically focusing on the Packham's Triumph cultivar in the Western Cape, South Africa. PSHB-FE is recognized globally as a destructive pest–disease complex affecting a vast range of hardwood tree species, many of which are important to agriculture, forestry, and urban landscaping. The presence of such a destructive pest in the economically vital fruit production industry, where its full impact is yet unknown, is alarming. The study primarily evaluates the physiological and phenological responses of commercial pear trees to different levels of infestation and explores how these responses affect fruit quality, water-use efficiency (WUE), and leaf traits. After the first year of invasion, we assess the early impact of PSHB-FE on fruit quality and WUE and examines the phenotypic plasticity of tree responses to infestation. It highlights that high PSHB attack density is associated with smaller, sweeter, and duller-coloured fruit, along with reduced WUE, even in asymptomatic trees. In the second year of invasion, the assessment zoomed into the physiological and phenological changes in the host trees due to PSHB-FE infestation. Here no significant physiological stress or disruption to phenological timing was detected. The research also evaluates the potential of multispectral vegetation indices (VIs) for early detection and monitoring of PSHB-FE invasion in commercial pear crops, highlighting their application in agricultural settings. While VI results aligned with the physiological assessments, the absence of clear physiological stress in the trees limited the ability to correlate VIs with specific PSHB-FE-induced stress parameters. Overall, the risk of PSHB-FE to commercial pear production appears lower than initially anticipated. However, early stages of invasion may still significantly impact production and the continued presence of PSHB-FE in orchards cannot be disregarded. The study highlights underlying inconsistency in the water-use dynamics of highly infested trees, suggesting potential management challenges if water use becomes more variable during hot, dry productive seasons. Monitoring PSHB populations during these periods will be critical. Invasion in this orchard was likely opportunistic, facilitated by prolific hosts in surrounding vegetation, since PSHB breeding in Packham’s Triumph pears is poor and infrequent, and PSHB activity seemingly declined in the second year. We propose that any resulting stress to pear host trees closely mirrors prevailing climatic conditions and PSHB-FE activity, rather than compounding over consecutive seasons of invasion. This response may extend to other deciduous fruit species with low breeding susceptibility. Our observations emphasize the importance of safely removing infested breeding hosts surrounding orchards and call for continued research on the susceptibility of various fruit species and cultivars to PSHBFE. The findings from this study are expected to inform future research and orchard management and pest monitoring strategies to mitigate and better understand the threat posed by this invasive pest complex. | en_ZA |
| dc.description.version | Masters | en_ZA |
| dc.format.extent | 65 pages | en_ZA |
| dc.identifier.uri | https://scholar.sun.ac.za/handle/10019.1/131858 | |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.title | The impact of the polyphagous shot hole borer beetle and its fungal symbiont, Fusarium euwallaceae, on commercial pear production | en_ZA |
| dc.type | Thesis | en_ZA |