Biology and control of Sclerotium rolfsii on groundnut in South Africa
| dc.contributor.advisor | Pretorius, Z. A. | |
| dc.contributor.advisor | Van Wyk, P. S. | |
| dc.contributor.author | Cilliers, André John | |
| dc.date.accessioned | 2017-03-23T06:33:36Z | |
| dc.date.available | 2017-03-23T06:33:36Z | |
| dc.date.issued | 2001-05 | |
| dc.description.abstract | English: Information gleaned from this study has stimulated new questions regarding the genetic structure, population dynamics and control of Sclerotium rolfsii. This work can hopefully serve as a foundation for the further study of this fungus in South Africa and elsewhere in the world. The population of the fungus in South Africa was studied and the 121 isolates collected were found to belong to 13 different mycelial compatibility groups (MCG), occurring on various crop and other plants in different geographic localities. Vague associations between MCG, host plant and geographical area could be observed. The genetic fingerprinting technique of amplified fragment length polymorph isms was found to be an effective tool to distinguish between MCGs of S. rolfsii. This technique has never before been used for this purpose, even though other genetic techniques have been used in other studies. No previous study, however, was able to distinguish isolates within MCGs, as this study was able to do. The hypothesis was also made that isolates within a MCG are not clonally derived, based on the differences observed between isolates in the same MCG, the different host plants and the different geographic areas from which the isolates originated. The pathogenicity of MCGs of S. rolfsii to groundnut appeared to be significantly different from group to group, but the results of field trials suggested that isolates were not fixed into specific MCGs, even though a controlled glasshouse experiment did not support this. The phenomenon of MCG switching has never been reported for this fungus, even though it has been recorded for other fungi. Certain isolates also appeared to be more pathogenic to groundnut than others. Mycelial compatibility group E consistently emerged as a virulent pathogen of groundnut. No groups were found to e specific to any of three other crop plants tested. The control of the fungus in groundnut fields was found to be possible with the use of an inversion plough in trials conducted over two consecutive seasons. A fungicide was identified that suppressed S. folfsii but not Trichoderma harzianum, a naturally occurring biological antagonist of the pathogen in the soil. The application of the fungicide difenoconazole at 12.5% of the registered concentration for groundnuts did not reduce disease in the field. The application of T. harzianum and difenoconazole in the early stages of groundnut plant development had no effect on yield or disease incidence. levels of disease in the field were found to increase with a decreased plant density. This observation was attributed to increased soil erosion in the field as a result of the sparser plant density. Sclerotium roltsii is a virulent pathogen of numerous crop plants in South Africa and this study has provided some answers to questions regarding the biology and control of this fungus. However, much still has to be discovered and may future scientists find some inspiration from what was done here. Key words: Sclerotium faItsii, southern stem rot, population, mycelial compatibility groups, AFlP analysis, pathogenicity, control, inversion plough, integrated pest management. | en_ZA |
| dc.description.abstract | Afrikaans: Die inligting wat in hierdie studie gegenereer is het nuwe vrae laat ontstaan oor die genetiese struktuur, populasie-dinamika en beheer van Sclerotium roltsii. Hopelik sal hierdie werk dien as 'n basis vir verdere studies oor hierdie swam in Suid Afrika en elders in die wêreld. Die populasie van die swam in Suid Afrika is bestudeer en 121 isolate, wat in 13 misiliêr-verenigbare groepe (MVGe) geklassifiseer kon word, is versamel. Die indeling van isolate binne hierdie groepe was tot In mindere mate gekoppel aan gasheerplant en/of geografiese gebied. Die genetiese vingerafdruktegniek van geamplifiseerde fragmentlengte polimorfismes ( "amplified fragment length polymorph isms" [AFLP]) kon effektief gebruik word om tussen die groepe te onderskei, sowel as tussen isolate in dieselfde groep. Hierdie tegniek is nog nooit voorheen gebruik vir hierdie doel nie, hoewel ander genetiese tegnieke wel in die verlede ondersoek is. Sodanige studies kon egter nog nooit tussen isolate binne dieselfde groep onderskei nie. Op grond van die variasie wat binne groepe met hierdie studie aangedui is kan die stelling ook gemaak word dat isolate binne 'n groep nie klonaalontstaan nie en ook omdat isolate in dieselfde groep van verskillende gasheerplante en gebiede kan kom. Die patogenisiteit van die verskillende groepe teenoor grondbone was verskillend tussen groepe, maar die data van veldproewe het daarop gedui dat isolate nie noodwendig tot In spesifieke MVG beperk is nie. 'n Onafhanklike proef, onder beheerde toestande in In glashuis, het egter gewys dat isolate nie binne groepe verander nie. Die verskynsel van verandering tussen MVGs is nog nooit vir S. roltsii aangeteken nie, alhoewel dit by ander swamme waargeneem is. Sekere isolate was ook meer aggresief teenoor grondbone as ander binne dieselfde groep. Groep E was deurgaans die mees virulente groep op grondbone. Geen groepe was spesifiek tot enige van die ander gewasse wat getoets is nie. Beheer van grondboonstamvrot oor twee agtereenvolgende seisoene is verkry waar besmette lande met 'n inversieploeg bewerk is. 'n Swamdoder is ook geidentifiseer wat S. rolfsii onderdruk terwyl die patogeen se natuurlike antagonis, Trichoderma harzianum, nie benadeel word nie. Die toediening van die fungisied difenoconazole teen 12.5 % (31 g/kg aktiewe bestandeel) van die voorgestelde toedieningskonsentrasie vir blaarsiektes van grondbone, het nie S. rolfsii infeksie onder landtoestande beheer nie. Proefresultate het ook getoon dat die toediening van die biologiese middel in kombinasie met die swamdoder vroeg in die seisoen geen effek op siekte of opbrengs gehad het nie. Onder veldtoestande het siekte toegeneem soos plantdigtheid verlaag het. Die rede hiervoor is waarskynlik die skade veroorsaak deur wind-erosie, wat toeneem soos die plantpopulasie afneem. Sclerotium rolfsii is 'n virulente patogeen van baie gewasse in Suid-Afrika en hierdie studie het slegs sekere antwoorde op vrae rondom die biologie en beheer verskaf. Die studieveld is dus nog oop vir verdere navorsing en die hoop word uitgespreek dat die huidige werk as inspirasie sal dien vir verdere navorsing oor hierdie onderwerp. | af |
| dc.description.sponsorship | Agricultural Research Council (ARC) | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11660/5974 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Sclerotium rolfsii | en_ZA |
| dc.subject | Southern stem rot | en_ZA |
| dc.subject | Population | en_ZA |
| dc.subject | Mycelial compatibility groups | en_ZA |
| dc.subject | AFLP analysis | en_ZA |
| dc.subject | Pathogenicity | en_ZA |
| dc.subject | Control | en_ZA |
| dc.subject | Inversion plough | en_ZA |
| dc.subject | Integrated pest management | en_ZA |
| dc.subject | Peanuts -- South Africa -- Diseases and pests | en_ZA |
| dc.subject | Thesis (Ph.D. (Plant Pathology))--University of the Free State, 2001 | en_ZA |
| dc.title | Biology and control of Sclerotium rolfsii on groundnut in South Africa | en_ZA |
| dc.type | Thesis | en_ZA |