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dc.contributor.advisorMcLaren, N. W.
dc.contributor.advisorVan der Westhuizen, A.
dc.contributor.authorVan Rooyen, Danelle
dc.date.accessioned2016-01-07T13:13:38Z
dc.date.available2016-01-07T13:13:38Z
dc.date.copyright2012-02
dc.date.issued2012-02
dc.date.submitted2012-02
dc.identifier.urihttp://hdl.handle.net/11660/2059
dc.description.abstractEnglish: Crop losses are estimated at 30% for sorghum annually as a result of invasion of pathogens or pests. Root rot is usually the result of a complex of soilborne fungi such as Fusarium spp., Pythium spp., Macrophomina phaseolina, Colletotrichum graminicola and Periconia circinata and other fungi. Colonization of host plant tissues are dependant on the environment that favours a specific pathogen at a particular time and host predisposition. Fungi were isolated and tested for pathogenicity on two sorghum cultivars. Root discolouration as a measure of root infection indicated a range of host responses, from severe root rot to some isolates that suppressed root rot and stimulated host growth. Isolate Bet9-3 (unidentified) resulted in the highest percentage root rot on both PAN 8420 and PAN 8706W. In most cases an Isolate x Cultivar interaction was recorded indicating that cultivars differ in their responses to pathogens although overall, PAN 8706W was more resistant to root rot than PAN 8420. All the isolates were identified by means of sequencing. A number of isolates that proved capable of causing severe root damage could not be identified suggesting that species, not previously identified, may be associated with root rots locally. Similarly, a number of species were isolated that have not previously been recorded on sorghum. Ergosterol concentrations in sorghum roots were used as a measure of root colonization by the test isolates. Isolate Bet26-4 (Acremonium strictum) resulted in the highest ergosterol level but with a moderate root rot discolouration. This disparity between the two evaluation criteria has resulted in the reliability of the evaluation criteria generally used to evaluate root rot, being questioned. Root rot severity, flag leaf length, total plant length, root volume and effective root volume of 26 sorghum cultivars from the National Cultivar Trials, planted in a naturally infested field trial at Cedara, were measured. All the cultivars were susceptible to root rot with PAN 8389 being the most susceptible (45.60%) and PAN 8534 the most resistant (29.23%). No significant relationship between root rot, root volume or effective root volume and plant growth parameters was recorded. A study using root extracts from the different cultivars showed only limited suppression of test fungal growth. Similarly, extractable phenol content from roots showed a tendency with reduced root rot severity in the field but this relationship was not significant. Some of the highest phenol content was observed in roots of PAN 8706W and PAN 8648W (white tan cultivars) and these cultivars had the second and third lowest root rot severities respectively. The high phenol content in roots of these cultivars is contrary to the low phenol contents normally reported in white sorghums and further studies of root physiology in relation to root rot resistance, as well as other mechanisms of root rot resistance, are warranted. The negative effects and risks associated with the use of agricultural chemicals have led to the search and discovery of new methods of disease control in plants. The potential of Trichoderma spp. associated with field sorghum as biological control agents was considered. Trichoderma spp. isolated from sorghum roots were tested for their effect on the growth of root sorghum isolates. In vitro inhibition of these isolates of up to 80 % was recorded due to modes of action including direct colonization and the production of volatile and non-volatile substances by Trichoderma spp. Trichoderma spp. differed in their ability to colonize sorghum seed, rhizospheres and roots. In a greenhouse study, in soil infested with sorghum root pathogens, Ced3-1 (T. hamatum) resulted in the lowest root rot severity while Kl23-1 (T. virens) had the least suppressive effect on disease development. Although Trichoderma spp. differed in their efficacy to suppress root rot, none was sufficiently so to be of significant commercial value.en_ZA
dc.description.abstractAfrikaans: Gewasverliese as ‘n direkte gevolg van patogene of peste word jaarliks op ongeveer 30% vir sorghum beraam. Wortelvrot is gewoonlik die gevolg van ‘n kompleks van grondgedraagde fungi soos Fusarium spp., Pythium spp., Macrophomina phaseolina, Colletotrichum graminicola en Periconia circinata en verskeie ander fungi. Die kolonisering van gasheerweefsel is afhanklik van die omgewing wat ‘n spesifieke patogeen bevorder op ‘n bepaalde tydstip, asook die vatbaarheid van die gasheer. Fungi is geïsoleer en getoets vir patogenesiteit op twee sorghum kultivars. Wortel verkleuring as ‘n aanduiding van wortel infeksie, het ‘n reeks gasheer reaksies aangedui, van strawwe wortelvrot tot die onderdrukking van wortelvrot en gestimuleerde plantegroei. Isolaat Bet 9-3 (onbekend) het die hoogste persentasie wortelvrot veroorsaak op beide PAN 8420 en PAN 8706W. In die meeste gevalle is ‘n Isolaat x Kultivar interaksie waargeneem wat aandui dat kultivars verskil in hulle reaksies teenoor patogene, alhoewel PAN 8706W in die algemeen meer weerstandbiedend was. Al die isolate is geïdentifiseer deur DNS nukleotied volgorde bepaling. Verskeie isolate wat instaat was om strawwe wortelvrot te veroorsaak, kon nie suksesvol geïdentifiseer word nie, wat aandui dat plaaslike, onbekende spesies dalk ‘n rol speel by wortelvrot. So ook is spesies geïdentifiseer wat nog nie vantevore op sorghum gerapporteer is nie. Vir bevestigingsdoeleindes is ergosterol vlakke in sorghum wortels gemeet om die koloniseringspotensiaal van die isolate te bepaal. Isolaat Bet 26-4 (Acremonium strictum) het hoë ergosterol vlakke getoon, alhoewel net ‘n gemiddelde wortelvrotstrafheid deur hierdie isolaat veroorsaak is. Hierdie waarnemings het daartoe gelei dat die betroubaarheid van huidige evaluasie tegnieke bevraagteken word. Die strafheid van wortelvrot, vlagblaar lengte, totale plant lengte en wortel volume van 26 sorghum kultivars van die Nasionale Kultivar Proewe, in ‘n veldproef in Cedara wat natuurlik met sorghum patogene besmet is, is gemeet. Al die kultivars was vatbaar vir wortelvrot met kultivar PAN 8389 die vatbaarste (45.60%) in vergelyking met PAN 8534 wat die meeste weerstand gebied het (29.23%). Geen betekenisvolle verhouding tussen wortelvrot, wortel volume en groei parameters was aangeteken nie. Slegs ‘n beperkte groei inhibisie is ondervind in ‘n studie waarin wortel ekstrakte teenoor fungi groei getoets is. Die vlak van geëkstraheerde fenool vanaf wortels het ‘n tendens met verminderde wortelvrot strafheid getoon, maar die verhouding was nie betekenisvol nie. Sommige van die hoogste fenool vlakke is in wortels van PAN 8706W en PAN 8648W (beide wit kultivars) aangetref en hiedie kultivars het ook die tweede en derde laagste wortelvrot strafheid getoon. Die hoë fenool vlakke in hierdie kultivar wortels stem nie ooreen met die algemene lae verwagte hoeveelhede wat gewoonlik in wit sorghum aangetref word nie. Verdere studies is dus nodig om wortel fisiologie in verhouding met weerstand, sowel as ander weerstandsmeganismes, te ondersoek. Die negatiewe effekte en risikos wat met die gebruik van landbou chemikalieë gepaard gaan, het gelei tot die soektog na nuwe metodes om plantsiektes te beheer. Die potensiaal van Trichoderma spp. as biologiese beheer agent is oorweeg. Trichoderma spp. wat geïsoleer is vanaf sorghum wortels is getoets teenoor swam isolate vanaf sorghum wortels. Tot 80% inhibisie van patogeen isolate is aangeteken, deur of direkte kontak of deur die produksie van vlugtige of nie-vlugtige stowwe wat produseer word deur Trichoderma spp. Trichoderma spp. het veskil ten opsigte van hul potensiaal om die sorghum saad, rhizosfeer en wortels te koloniseer. In die kweekhuis het Ced3-1 (T. hamatum) die meeste wortelvrot onderdrukking getoon teenoor Kl23-1 (T. virens) wat die minste inhibisie getoon het. Alhoewel Trichoderma spp. verkil het in hul meganismes om wortelvrot te onderdruk, was dit nie suksesvol genoeg vir kommersiële gebruik nie.af
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectSorghum -- Disease and pest resistanceen_ZA
dc.subjectSorghum root and stalk rotsen_ZA
dc.subjectRoot rotsen_ZA
dc.subjectFusariumen_ZA
dc.subjectDissertation (M.Sc. (Plant Pathology ))--University of the Free State, 2012en_ZA
dc.titleThe resistance of grain sorghum to the root rot pathogen complexen_ZA
dc.typeDissertationen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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