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Epidemiology and post-harvest management of the sexual state of Erysiphe necator
Thesis (MScAgric)--Stellenbosch University, 2025.
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867613973250048000 |
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| access_status_str | Open Access |
| author | Janse van Rensburg, Kara Rain |
| author2 | Havenga, Minette |
| author_browse | Havenga, Minette Janse van Rensburg, Kara Rain |
| author_facet | Havenga, Minette Janse van Rensburg, Kara Rain |
| author_sort | Janse van Rensburg, Kara Rain |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MScAgric)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/132529 |
| institution | Stellenbosch University (South Africa) |
| last_indexed | 2026-06-10T12:44:38.662Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/132529 Epidemiology and post-harvest management of the sexual state of Erysiphe necator Janse van Rensburg, Kara Rain Havenga, Minette Halleen, Francois Mostert, Lizel Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology. Erysiphe necator -- Epidemiology Powdery mildew diseases -- Management Grapes -- Seasonal variations -- South Africa Vineyards -- Climatic factors -- South Africa Plant diseases -- Epidemics -- Economic aspects Grapes -- Postharvest diseases and injuries Grapes -- Effect of environment on UCTD Thesis (MScAgric)--Stellenbosch University, 2025. Janse van Rensburg, K. R. 2025. Epidemiology and post-harvest management of the sexual state of Erysiphe necator. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/9a3b4af2-8056-4fb7-99fd-e03c0cc601ea ENGLISH ABSTRACT: Erysiphe necator causes powdery mildew on grapevines leading to severe economic losses globally. Despite its impact, little is known regarding the epidemiology in South Africa. In 1996 and 1997, only a few immature chasmothecia were detected in three vineyards and flag shoots in one vineyard in South Africa. However, in 2016, larger numbers of mature chasmothecia were detected in a wider geographical range. The aim was to investigate the epidemiology of powdery mildew and determine the effect of post-harvest treatments on chasmothecia. Symptomatic plant material was sampled from 105 commercial vineyards and chasmothecia were observed in 72 vineyards in all six climatic and seven grape-growing regions surveyed. Chasmothecia were observed on leaves, shoots, rachises, bunches, bark, leaf litter and secondary crop bunches. The epidemiology of powdery mildew was monitored biweekly for two seasons in four commercial vineyards. Immature yellow chasmothecia were generally detected from March, however, it was detected in some vineyards as early as January. The highest numbers of mature chasmothecia were detected in March and May for wine and table grape vineyards, respectively. Less viable chasmothecia were observed in 2024 compared to 2023 most likely due to higher temperatures in 2024. Bark, leaf litter and pruning debris were sampled, mature chasmothecia harvested, counted and their viability assessed. Chasmothecia were detected on bark, leaf litter and pruning debris in both seasons. However, the number of chasmothecia decreased between leaf fall and bud break, due to ascospore release throughout winter when weather conditions were conducive. The premature release could result in inoculum depletion, however, viable chasmothecia were detected on bark and pruning debris at bud break. Despite high numbers of chasmothecia on leaf litter at leaf fall, no chasmothecia were detected on leaf litter at bud break. The mating-type ratio did not deviate significantly from 1:1 for powdery mildew sampled from leaves. The vineyards were monitored biweekly for flag shoots and emerging leaves and shoots were harvested from bud break for 10 weeks. No flag shoots were detected in commercial vineyards, however, one flag shoot was found in a garden. The haplotypes present in the vineyards over time were determined by sequencing the ITS, IGS, TUB2 and EF1-⍺ gene regions for 37 isolates. Three haplotypes (SA1, SA2, SA3), all belonging to biotype B were identified which were identical to haplotypes 41, 43 and 44 known from Europe and Western USA. No patterns of temporal or geographical distribution of haplotypes could be identified. The effect of a post-harvest treatment was assessed on four and 10 vineyards in 2023 and 2024, respectively by sampling symptomatic leaves before and after treatment. Yellow chasmothecia decreased in two and five vineyards in 2023 and 2024, respectively likely due to the low lipid content of yellow chasmothecia making it more permeable. Little effect was observed for black chasmothecia. A detached leaf assay was used to assess the effect of 10 fungicide actives and a biological control agent (Ampelomyces quisqualis) on the viability of chasmothecia. Seven fungicide actives and A. quisqualis had viable chasmothecia ranging between 62.50% and 76.63% which was significantly lower than the water control (92.15%). Post-harvest treatments may be most effective when applied shortly after harvest when powdery mildew infection is low or when the majority of chasmothecia is yellow. This was the first study i) that reported viable chasmothecia from pruning debris, ii) investigated the haplotypes in South African E. necator populations and iii) investigated the effect of a post-harvest treatment on immature chasmothecia. Further research should investigate the sensitivity of powdery mildew to important fungicide actives to be able to develop effective management strategies. AFRIKAANSE OPSOMMING: Erysiphe necator veroorsaak poeieragtige meeldou op wingerd wat lei to ernstige ekonomiese verliese wêreldwyd. Ten spyte van die impak daarvan, is min bekend oor die epidemiologie in Suid-Afrika. In 1996 en 1997 is slegs enkele onvolwasse geslagtelike strukture in drie wingerde en vlaglote in een wingerd in Suid-Afrika gevind. In 2016 is groter hoeveelhede volwasse geslagtelike strukture in 'n wyer geografiese area gevind. Die doel was om die epidemiologie van poeieragtige meeldou te ondersoek en die effek van enkele na-oes behandelings op geslagtelike strukture te bepaal. Simptomatiese plantmateriaal is van 105 kommersiële wingerde gemonster en geslagtelike strukture is in 72 wingerde in al ses klimaats- en sewe groeistreke gevind. Geslagtelike strukture is waargeneem op blare, lote, trosse, bas, blaar afval en natrosse. Die epidemiologie van poeieragtige meeldou is tweeweekliks vir twee seisoene in vier kommersiële wingerde gemonitor. Onvolwasse geel geslagtelike strukture is oor die algemeen vanaf Maart opgespoor maar dit was egter reeds in Januarie in sommige wingerde gevind. Die hoogste getalle volwasse geslagtelike strukture is onderskeidelik in Maart en Mei vir wyn- en tafeldruifwingerde waargeneem. Minder vatbare geslagtelike strukture is in 2024 waargeneem in vergelyking met 2023, waarskynlik as gevolg van hoër temperature in 2024. Bas, blaar afval en snoeiselafval is gemonster, volwasse geslagtelike strukture is geoes, getel en hul vatbaarheid getoets. Geslagtelike strukture is in beide seisoene op bas, blaar afval en snoeiselafval opgespoor. Die aantal geslagtelike strukture het egter tussen blaarval en bot afgeneem as gevolg van askospoorvrystelling deur die winter wanneer weerstoestande gunstig was. Vroeë askospoor vrystelling kan lei tot uitputting van inokulum, maar vatbare geslagtelike strukture is wel opgespoor op bas en snoeiselafval tydens bot. Ten spyte van hoë getalle geslagtelike strukture op blaar afval met blaarval, is geen geslagtelike strukture op blaar afval opgespoor met bot nie. Die paringstipe verhouding het nie betekenisvol van 1:1 afgewyk vir poeieragtige skimmel wat van blare gemonster is nie. Die wingerde is tweeweekliks gemonitor vir vlaglote en opkomende blare en lote is vir 10 weke vanaf bot getoets vir poeieragtige meeldou. Geen vlaglote is in kommersiële wingerde opgespoor nie, maar een vlaglot is in 'n tuin gevind. Die haplotipes teenwoordig in die wingerde oor tyd is bepaal deur die volgordebepaling van die ITS, IGS, TUB2 en EF1-⍺ geenareas vir 37 isolate. Drie haplotipes (SA1, SA2, SA3), almal wat aan biotipe B behoort, is geïdentifiseer wat identies was aan haplotipes 41, 43 en 44 wat bekend is van Europa en Wes-VSA. Geen patrone van tydelike of geografiese verspreiding van haplotipes kon geïdentifiseer word nie. Die effek van 'n na-oesbehandeling is op vier en 10 wingerde in 2023 en 2024 onderskeidelik getoets deur simptomatiese blare voor en na behandeling te neem. Geel geslagtelike strukture het onderskeidelik in twee en vyf wingerde in 2023 en 2024 afgeneem, waarskynlik as gevolg van die lae lipiedinhoud van geel geslagtelike strukture wat dit meer deurlaatbaar maak. Swart geslagtelike strukture was tot ‘n mindere mate geaffekteer. Die effek van 10 aktiewe bestandele en 'n biologiese beheermiddel (Ampelomyces quisqualis) op die vatbaarheid van die geslagtelike strukture was bepaal op simptomatiese blare in die laboratorium. Sewe aktiewe bestandele en A. quisqualis het vatbare geslagtelike strukture gehad wat wissel tussen 62.50% en 76.63% wat aansienlik laer was as die water kontrole (92.15%). Na-oes behandelings kan die doeltreffendste wees wanneer dit toegepas word kort na oes wanneer poeieragtige meeldou infeksie laag is of wanneer die meerderheid van die geslagtelike strukture geel is. Dit was die eerste studie i) wat vatbare geslagtelike strukture van snoeiselafval gerapporteer het, ii) die haplotipes in Suid-Afrikaanse E. necator populasies ondersoek het en iii) die effek van 'n na-oes behandeling op onvolwasse geslagtelike strukture ondersoek het. Verdere navorsing moet die sensitiwiteit van poeieragtige meeldou vir belangrike swamdoder aktiewes ondersoek om effektiewe bestuurstrategieë te ontwikkel. Masters 2025-06-10T12:59:28Z 2025-06-10T12:59:28Z 2025-03 Thesis https://scholar.sun.ac.za/handle/10019.1/132529 Stellenbosch University vii, [4], 129 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Erysiphe necator -- Epidemiology Powdery mildew diseases -- Management Grapes -- Seasonal variations -- South Africa Vineyards -- Climatic factors -- South Africa Plant diseases -- Epidemics -- Economic aspects Grapes -- Postharvest diseases and injuries Grapes -- Effect of environment on UCTD Janse van Rensburg, Kara Rain Epidemiology and post-harvest management of the sexual state of Erysiphe necator |
| title | Epidemiology and post-harvest management of the sexual state of Erysiphe necator |
| title_full | Epidemiology and post-harvest management of the sexual state of Erysiphe necator |
| title_fullStr | Epidemiology and post-harvest management of the sexual state of Erysiphe necator |
| title_full_unstemmed | Epidemiology and post-harvest management of the sexual state of Erysiphe necator |
| title_short | Epidemiology and post-harvest management of the sexual state of Erysiphe necator |
| title_sort | epidemiology and post harvest management of the sexual state of erysiphe necator |
| topic | Erysiphe necator -- Epidemiology Powdery mildew diseases -- Management Grapes -- Seasonal variations -- South Africa Vineyards -- Climatic factors -- South Africa Plant diseases -- Epidemics -- Economic aspects Grapes -- Postharvest diseases and injuries Grapes -- Effect of environment on UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/132529 |
| work_keys_str_mv | AT jansevanrensburgkararain epidemiologyandpostharvestmanagementofthesexualstateoferysiphenecator |