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dc.contributor.advisorPretorius, Z. A.
dc.contributor.advisorFlett, B.
dc.contributor.advisorVan Deventer, C. S.
dc.contributor.authorFato, Pedro
dc.date.accessioned2017-05-22T07:18:05Z
dc.date.available2017-05-22T07:18:05Z
dc.date.issued2000-11
dc.identifier.urihttp://hdl.handle.net/11660/6263
dc.description.abstractEnglish: Common rust, caused by Puccinia sorghi Schw., is a major disease in maize (Zea mays L.) producing regions throughout the world and can result in high yield losses on susceptible genotypes when the environment is favourable for epidemic development. To understand the principal aspects related to P. sorghi, a literature survey concerning the biology of the pathogen, host range, host-pathogen interaction, and economic importance of the disease, was conducted. Furthermore, different methods of disease management are reviewed, with emphasis on genetic control. To determine pathogenic variability in Puccinia sorghi in South Africa, rustinfected maize leaves were collected during the 1999/2000 season. Isolates collected in the field were increased on susceptible plants and inoculated onto maize differential lines carrying different Rp genes for resistance to P. sorghi. Seven pathotypes, namely, A, B, C, D, E, F and G, were differentiated in the greenhouse. Pathotype B was the most virulent and occurred in Gauteng, KwaZulu-Natal, and Mpumalanga. Pathotype A, virulent only on Rp34 and Rp3B/ was widely distributed, occurring in six provinces. Pathotype C was detected in Mpumalanga and the Northern Province, D in the Northern Province whereas pathotype E was collected from North West, and F and G from KwaZulu-Natal. No virulence was detected for genes Rp1C, Rp1G,Rp1L, Rp3D and Rp3F. All isolates were virulent on Rp3B. The occurrence of virulence for most Rp genes suggests that monogenic resistance is of little value for future protection of maize cultivars against common rust in South Africa. One hundred maize inbred lines from Mozambique, South Africa and Zimbabwe, as well as 58 South African hybrids, were evaluated for resistance to common rust under field conditions over different localities in South Africa during the 1999/2000 season. Inbred lines were planted at Ermelo and Greytown and inoculated by a mixture of spores from previously identified P. sorghi pathotypes. Cultivars were tested under conditions of natural common rust infection at Greytown and Petit. Disease severity was assessed prior to anthesis, at anthesis, and after anthesis at all localities except the Greytown cultivar trial, which was assessed only once after anthesis. Disease was scored on a 0-9 scale converted to percentage leaf diseased area (0-96% scale). The percentage values were log-transformed using the natural logarithm function. Analyses of variance were carried out for each severity parameter (individual rating, mean, sum and AUDPC [area under the disease progress curve]) within, and (mean, sum and AUDPC) across localities. Significant genetic variation existed between genotypes for resistance to P. sorghi at each and across localities. Some inbred lines showed significant levels of partial resistance to the pathogen and may be used in resistance breeding programmes. Most hybrids showed susceptible reaction types to common rust and are thus potentially vulnerable to yield losses under conditions of epidemic occurrence of P. sorghi. In general, similar to other cereal rust pathosystems, it is apparent that monogenic rust resistance in maize will not be durable. Emphasis in breeding should therefore be placed on horizontal resistance, with particular attention to sources of resistance, screening procedures and heritability. This study will hopefully serve as an important source of information for future research of common maize rust in southern Africa.en_ZA
dc.description.abstractAfrikaans: Roes, veroorsaak deur Puccinia sorghi Schw., is 'n belangrike siekte van mielies (Zea mays L.) wêreldwyd en kan betekenisvolle oesverliese veroorsaak onder omgewingstoestande gunstig vir epidemiese ontwikkeling. Ten einde die belangrikste aspekte met betrekking tot die biologie van patogeen, gasheerreeks, gasheer-patogeen interaksies en ekonomiese belang te verstaan, is n literatuuroorsig saamgestel. Verskillende metodes van siektebeheer, met spesiale klem op genetiese beheer, is ook ingesluit. Patogeniese variasie in P. sorghi in Suid-Afrika is gedurende die 1999/2000 seisoen bestudeer. Mielieblare geïnfekteer met roes is in die veld versamel en roeskulture is op vatbare plante in 'n glashuis vermeerder. Isolate is gesuiwer en vervolgens op roes-differensiërende lyne, elk met In bepaalde Rp-geen vir bestandheid, geïnokuleer. Sewe patotipes, nl. A, B, C, D, E, F en G, is geïdentifiseer. Patotipe B was mees virulent en is in Gauteng, KwaZulu-.Natal en Mpumalanga waargeneem. Patotipe A, slegs virulent op Rp34 en Rp3B, was wydverspreid in ses provinsies. Patotipe E het in Noordwes voorgekom terwyl F en G in KwaZulu-Natal, C in Mpumalanga en die Noordelike Provinsie, en D in die Noordelike Provinsie, onderskeidelik, versamel is. Geen virulensie is vir die gene Rp1C, Rp1G,Rp1L, Rp3D and Rp3F waargeneem nie. Alle isolate was virulent op Rp3B. Die voorkoms van virulensie vir meeste Rp-gene dui aan dat monogeniese weerstand van min waarde in die toekomstige beskerming van mieliekultivars teen roes in Suid-Afrika sal wees. Eenhonderd ingeteelde mielielyne vanaf Mosambiek, Suid-Afrika en Zimbabwe, en 58 Suid-Afrikaanse kultivars, is vir bestandheid teen roes onder veldtoestande gedurende 1999/2000 geëvalueer. Die lyne is op Ermelo en Greytown geplant en met 'n mengsel van spore van vooraf-bepaalde patotipes van P. sorghi geïnokuleer. Die kultivars is onder toestande van natuurlike infeksie op Greytown en Petit getoets. Siektegraad is voor, tydens, en na antese bepaal, behalwe vir die kultivarproef te Greytown waar roesinfeksie slegs eenmalig na antese beraam is. Siektegraad is gemeet op "n 0-9 skaal waarna die waardes omgeskakel is na "n persentasieskaal (0-96%). Die persentasie-waardes is vervolgens getransformeer na natuurlike logaritmes. Analise van variansie is uitgevoer op elke siekteparameter (individuele raming, gemiddelde raming, som van ramings en AOSVK [area onder die siektevorderingskurwe]) binne, en (gemiddeld, som en AOSVK) oor lokaliteite. Betekenisvolle genetiese variasie vir reaksie teenoor P. sorghi infeksie is waargeneem by elke lokaliteit, maar ook oor lokaliteite. Sekere ingeteelde lyne het hoë vlakke van gedeeltelike weerstand teen roes getoon en kan in weerstandstelingsprogramme gebruik word. Die meeste basters was egter vatbaar, wat aandui dat hulle potensieel gevoelig is vir oesverliese tydens toestande gunstig vir epidemiese ontwikkeling van mielieroes. Soortgelyk aan ander graanroes-patosisteme is dit duidelik dat monogeniese weerstand in mielies nie volhoubaar teen roes sal wees nie. Die klem in weerstandsteling moet dus val op horisontale weerstand, met spesifieke verwysing na toepaslike bronne, evaluasieprosedures en erflikheid. Hierdie studie sal hopelik dien as "n belangrike bron van inligting vir toekomstige navorsing op mielieroes in Suidelike Afrika.af
dc.description.sponsorshipCIMMYT-Zimbabween_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectCorn -- Diseases and pests -- South Africaen_ZA
dc.subjectCorn -- Disease and pest resistance -- Genetic aspectsen_ZA
dc.subjectDissertation (M.Sc.Agric. (Plant Breeding))--University of the Free State, 2000en_ZA
dc.titlePathogenic variability in Puccinia Sorghi on maize in South Africaen_ZA
dc.typeDissertationen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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