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dc.contributor.advisorPretorius, Z. A.
dc.contributor.authorKomen, Johannes Stephanus
dc.date.accessioned2018-01-19T10:29:52Z
dc.date.available2018-01-19T10:29:52Z
dc.date.issued2007-11
dc.identifier.urihttp://hdl.handle.net/11660/7644
dc.description.abstractEnglish: Stem rust caused by Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn., is an economically important disease of bread wheat (Triticum aestivum L.) worldwide. The disease has often reached epidemic proportions in South Africa. The release of rust-susceptible cultivars in South Africa is of great concern and therefore research is needed to determine if chemical control is an economically viable method to control rust diseases. The recent increase of stem rust in the Western Cape production area of South Africa has led to a renewed interest in the use of fungicides. In addition to chemical control, effective genetic control of rust diseases requires a coordinated effort, including pathotype monitoring, collection and characterization of sources of resistance, and resistance breeding. Data generated by pathotype surveys thus form an essential component of breeding programmes and are conducted by most wheat producing countries, principally to recognize pathogenic changes. The timely detection of stem rust pathotypes with new virulence is considered important to the South African wheat industry. A stem rust survey is conducted annually to monitor pathogenic variability in Puccinia graminis f. sp. tritici in the major bread wheat and triticale producing areas of South Africa. More than 70% of the isolates obtained from 2002 to 2004 were characterized as pathotype 2SA88, which unusual for local pathotypes, was virulent for Sr8b and Sr38. During the six year survey period, stem rust pathotypes 2SA4, 2SA55, 2SA88, 2SA99 and 2SA100 were detected on bread wheat and 2SA102, 2SA102K and 2SA103 on triticale. To optimize in vitro testing conditions the effect of temperature on germination and germ tube growth of P. graminis f. sp. tritici as well as incubation periods were evaluated. Seventy eight percent of urediniospores had germinated on water agar in petri dishes after 6 h of incubation at 20 and 25°C. Low germination rates were observed at 30°C. Twenty-nine fungicides in nine chemical classes were evaluated in vitro for toxicity to stem rust urediniospores. Water agar petri dish plates were amended with fungicides at concentrations ranging from 10 to 0.0001 μl active ingredient / ml medium. Low EC50 (effective concentration that results in 50% inhibition) values were obtained with azoxystrobin, trifloxystrobin, kresoxim-methyl, mancozeb, azoxystrobin/ difenoconazole, iprodione, chlorothalonil and hexoconazole. A shorter residual effect of trifloxystrobin occurred in wheat infected with stem rust in a glasshouse assay, whereas longer efficacy periods were determined for azoxystrobin/difenoconazole and tebuconazole. Fungicide field trials were conducted at Greytown, South Africa to determine the effect of rust diseases on yield and test weight. Information on the efficacy of different foliar treatments in controlling these diseases was obtained. Although the emphasis was on stem rust, it was not possible to eliminate leaf rust from the field trials. In 2005, 92% of the yield reduction experienced was contributed by leaf rust infection whereas in 2006 32% of losses could be attributed to this disease. Stem rust on the other hand contributed 8% to losses in 2005 and 68% in 2006. Yield increase resulting from fungicide applications ranged from 36% to 45% over the two years. With a flag leaf treatment the mean yield increase per plant was 21% compared to 43% with a multiple-spray treatment in 2005. The highest yield increase was obtained with tebuconazole resulting in a 58% gain. Test weight increased by 29% with fungicide applications over the control plots. Further research is needed to optimize control by means of fungicides.en_ZA
dc.description.abstractAfrikaans: Stamroes, veroorsaak deur Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn., is ‘n ekonomies belangrike siekte op broodkoring (Triticum aestivum L.) wêreldwyd. Die siekte het gereeld epidemiese afmetings in Suid-Afrika aangeneem. Die vrystelling van vatbare kultivars is kommerwekkend en navorsing is nodig om te bepaal of chemiese beheer ‘n ekonomies-regverdigbare uitweg is om roessiektes te beheer. Die toename in stamroes in koringproduksiegebiede van die Wes-Kaap, Suid Afrika het gelei tot die algemene gebruik van swamdoders. Bo en behalwe chemiese beheer benodig effekiewe genetiese beheer van roessiektes ‘n gekoördineerde poging insluitende patogeniese monitering, verkryging en karakterisering van weerstandsbronne en weerstandsteling. Data verkry vanaf patogeniese waarneming vorm ‘n essensiële komponent van ‘n teelprogram en word uitgevoer deur die meeste koringproduserende lande. Om stamroespatotipes betyds te identifiseer, veral ten opsigte van nuwe virulensie, is belangrik vir die Suid-Afrikaanse koringbedryf. Stamroesopnames word jaarliks uitgevoer om die patogeniese variasie van P. graminis f. sp. tritici in die belangrike koring en triticale produserende areas van Suid Afrika te moniteer. Meer as 70% van die isolate verkry gedurende 2002-2004 is gekarakteriseer as patotipe 2SA88, wat, ongewoon vir plaaslike patotipes, virulent is vir Sr8b en Sr38. Gedurende ‘n sesjaar periode is stamroespatotipes 2SA4, 2SA55, 2SA88, 2SA99 en 2SA100 geïdentifiseer op broodkoring terwyl patotipes 2SA102, 2SA102K en 2SA103 geïdentifiseer is op triticale. Om in vitro toetse te optimiseer is die effek van temperatuur op ontkieming en kiembuislengte van P. graminis f. sp. tritici, sowel as inkubasieperiode geëvalueer. Agt en sewentig persent van urediniospore het ontkiem op wateragar petribakkies na 6 h van inkubasie by 20 en 25°C. Lae ontkiemingswaardes is verkry by 30°C. Nege-en-twintig swamdoders in nege chemiese groepe is in vitro getoets vir toksisiteit teenoor stamroesurediniospore. Swamdoders teen konsentrasies van 10 tot 0.0001 μl aktiewe bestanddeel per ml medium is by petribakkies met wateragar gevoeg. Lae EK50 waardes (effektiewe konsentrasie wat lei tot 50% inhibisie) is verkry met azoxystrobin, trifloxystrobin, kresoxim-methyl, mancozeb, azoxystrobin/ difenoconazole, iprodione, chlorothalonil en hexoconazole. ‘n Korter nawerking is verkry met trifloxystrobin op koring geïnfekteer met stamroes in glashuistoetse, terwyl azoxystrobin/difenoconazole en tebuconazole langer nawerkingsperiodes getoon het. Swamdoderveldproewe is uitgevoer by Greytown, Suid Afrika om die effek van roessiektes op opbrengs en 1000-korrel massa te bepaal. Inligting oor die effektiwiteit van verskillende blaarbespuitings in die beheer van die siektes is verkry. Al was die primere fokus gerig op stamroes, kon daar nie verhoed word dat blaarroes die proewe infekteer nie. In 2005 is 92%, en in 2006, 32% van die opbrengsverliese veroorsaak deur blaarroesinfeksies. Stamroes het bygedra tot 8% van verliese in 2005 en 68% in 2006. Opbrengsverhoging verkry deur swamdodertoediening het gewissel van 36% tot 45% oor die tweejaarperiode. In 2005 is die gemiddelde opbrengs per plant verhoog met 21% deur ‘n vlagblaarbespuiting, vergeleke met 43% met herhaalde bespuitings. Die hoogste opbrengs verhoging is verkry met tebuconazole (58%). Duisendkorrelmassa het verhoog met 29% vergeleke met die kontrole. Verdere navorsing is nodig om chemiese beheer te optimaliseer.af
dc.description.sponsorshipPannar Pty. Ltd.en_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectWheat -- Diseases and pestsen_ZA
dc.subjectWheat -- Disease and pest resistanceen_ZA
dc.subjectWheat rusts -- South Africaen_ZA
dc.subjectPuccinia graminisen_ZA
dc.subjectDissertation (M.Sc.Agric. (Plant Sciences: Plant Pathology))--University of the Free State, 2007en_ZA
dc.titleStudies on chemical control of wheat stem rusten_ZA
dc.typeDissertationen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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