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dc.contributor.advisorPretorius, Z. A.
dc.contributor.authorPienaar, Lizaan
dc.date.accessioned2018-01-19T10:44:49Z
dc.date.available2018-01-19T10:44:49Z
dc.date.issued2004-05
dc.identifier.urihttp://hdl.handle.net/11660/7646
dc.description.abstractEnglish: The objective of this study was to develop and optimise methods to detect adult-plant resistance (APR) in wheat to stripe rust caused by Puccinia striiformis f.sp. tritici. A collection of spring wheats was tested at the seedling stage with different temperature and light regimes to test the hypothesis that environmental variation can induce APR expression in primary leaves. Treatments included pre-inoculation conditioning of seedlings at either 18° or 25°C, followed by post-inoculation temperature and light treatments. In some treatments intermittent low and high temperatures (18° or 25°C) were used as well as a treatment with continuous low temperature (10°C). The highest infection types were encountered with a pre-inoculation treatment of 18°C combined with a 24 h light cycle, and a post-inoculation treatment of 18°C combined with a 18 h light and 6h darkness cycle. Day length influenced infection types more than temperature. All treatments subjected to less than 14 h light per day showed a reduction in infection levels. Dark periods experienced prior to inoculation were not conducive to infection type development. Clear banding of infection zones and reduced sporulation occurred. Based on the lack of correlation between seedling infection types and adult responses observed in the field, no environment was conducive to expression of APR to stripe rust in seedlings. Rating of adult plants for stripe rust resistance has traditionally been problematic in terms of infection levels and repeatability. Furthermore, several attempts to investigate the reaction of normally grown adult plants in the glasshouse failed due to leaf damage. To improve these methods, an accelerated system of producing adult wheat plants in a controlled environment was tested. By manipulating plant density, pot size, light and temperature, wheat plants reached maturity quicker than normally grown adult plants and were referred to as mini-adult plants. In terms of leaf damage the mini-adults were better suited for flag (terminal) leaf evaluation. For optimum results, the mini-adult plants should be grown in a glasshouse rather than growth chamber and inoculated between heading and flowering. According to flag leaf infection type and whole plant reactions observed, the mini-adults provided an acceptable system for comparing adult plants to different isolates of P. striiformis. This system accurately detected APR in most winter wheats tested and was reliable for a collection of CIMMYT spring type wheats. Disease ratings of 98 CIMMYT lines tested with this accelerated system showed a correlation of 88% with field ratings. The mini-adult plant system was also tested with populations segregating for APR. Because of the likely application of genetic studies to resistance breeding, it is essential to correlate glasshouse tests with field assessments. The approach followed in the present study conformed to guidelines in terms of selecting cultivars with high levels of APR not previously analysed, as well as comparing glasshouse and field data. Segregation ratios indicated the presence of two resistance genes in the F3 of a Baviaans x Avocet S cross (χ²7:8:1 = 0.1029), but were inconclusive for a Sunmist x Avocet S cross where Mendelian ratios could not be confirmed. The accelerated screening system was less successful than the screening of pure lines. Based on the fact that the reaction of Avocet S was not completely susceptible in the glasshouse, and most likely influenced ratios, the lower success rate appeared to be a function of the parental genotypes rather than in the system in general. Compared to the normal glasshouse procedure, the improved APR system took significantly less time and physical resources to achieve ratings.en_ZA
dc.description.abstractAfrikaans: Die doel van hierdie studie was om ‘n metode te ontwikkel en te optimiseer waarmee volwasse-plantweerstand (VPW) in koring teen streeproes (Puccinia striiformis f.sp. tritici) geïdentifiseer kan word. ‘n Versameling lentekorings is op saailingstadium aan verskillende temperatuur- en ligbehandelings blootgestel om die hipotese te toets dat omgewingstoestande VPW in saailinge tot uiting kan bring. Behandelings het bestaan uit voor-inokulasie blootstelling van saailinge aan 18° of 25°C, gevolg deur na-inokulasie temperatuur- en ligbehandelings. In sommige behandelings is lae en hoë temperature (18° of 25°C) afwisselend getoets, en in ander volgehoue lae temperatuur (10°C). Die hoogste infeksietipes is verkry met ‘n voor-inokulasie temperatuur van 18°C gekombineer met 24 h lig behandeling, en ‘n na-inokulasie temperatuur van 18°C, met ‘n kombinasie van 18 h lig en 6 h donker periode. Alle behandelings wat minder as 14 h ligblootstelling gehad het, het ‘n afname in infeksietipe getoon. Donker periodes voor inokulasie het nie goeie infeksie tot gevolg gehad nie. Infeksie het in duidelike bande voorgekom, met verminderde sporulasie. As gevolg van die swak korrelasie tussen die saailing infeksietipes en volwasse-plantreaksies in die veld, is tot die gevolgtrekking gekom dat omgewing nie VPW akkuraat in saailinge uitdruk nie. Lesings van volwasse-plantreaksies is tradisioneel moeilik in terme van infeksie vlakke en herhaalbaarheid. Verskeie pogings om die reaksie van normaal gekweekte volwasse plante in die glashuis te toets het misluk weens blaarskade. Om hierdie metode te verbeter, is ‘n versnelde sisteem ontwikkel wat volwasse plante in ‘n beheerde omgewing toets. Deur plantdigtheid, potgrootte, lig en temperatuur te manipuleer is die volwasseplantstadium vinniger bereik as met normale plante, en word na hulle verwys as mini-volwasse plante. In terme van blaarbeskadiging, het die mini-volwasse plante beter vlagblaarreaksies getoon. Vir optimale resultate moet die mini-volwasse plante eerder in die glashuis as in groeikabinette gekweek word, en geïnokuleer word tussen aarvorming en blomstadium. Na aanleiding van vlagblaarinfeksietipe en totale plantreaksie, bied mini-volwasse plante ‘n aanvaarbare sisteem om verskillende streeproes-isolate met mekaar te vergelyk. Die sisteem het VPW akkuraat in meeste winterkorings asook in ‘n versameling CIMMYT lentekorings beskryf. Siektelesings van 98 CIMMYT lyne is getoets met hierdie versnelde sisteem en het 88% gekorrelleer met die veldreaksies. Die mini-volwasse sisteem is ook getoets met populasies wat segregeer vir VPW. As gevolg van die toepassing van genetiese studies in weerstandsteling, is dit noodsaaklik om glashuistoetse met veldreaksies te vergelyk. Die benadering gevolg in hierdie studie het gehou by riglyne in terme van seleksie van kultivars met hoë weerstandsvlakke, wat nie voorheen getoets is nie, asook om glashuisdata met velddata te vergelyk. Segregasie-verhoudings het gedui op die teenwoordigheid van twee weerstandsgene in die F3 van ‘n Baviaans x Avocet S kruising (χ²7:8:1 = 0.1029), maar was onbeduidend vir die Sunmist x Avocet S kruising ten opsigte van Mendeliese segregasie-verhoudings. Die versnelde sisteem was minder suksesvol vir genetiese studies as vir die evaluasie van suiwertelende lyne. As gevolg van die feit dat Avocet S nie volkome vatbaar was in die glashuis nie, wat ook vermoedelik die segregasieverhoudings beïnvloed het, kan die verlaagde sukses eerder toegeskryf word aan die ouergenotipe as aan die sisteem in die algemeen. Die versnelde sisteem benodig betekenisvol minder tyd en fisiese hulpbronne om akkurate lesings te produseer.af
dc.description.sponsorshipNational Research Foundation (NRF)en_ZA
dc.description.sponsorshipWinter Cereal Trusten_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectStripe rust -- South Africaen_ZA
dc.subjectWheat -- Disease and pest resistance -- South Africaen_ZA
dc.subjectWheat rusts -- South Africaen_ZA
dc.subjectDissertation (M.Sc.Agric. (Plant Sciences (Plant Pathology))--University of the Free State, 2004en_ZA
dc.titleAssessment of adult plant resistance to stripe rust in wheaten_ZA
dc.typeDissertationen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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