Biology and control of Sclerotium rolfsii on groundnut in South Africa

[摘要] English: Information gleaned from this study has stimulated new questions regarding the geneticstructure, population dynamics and control of Sclerotium rolfsii. This work can hopefullyserve as a foundation for the further study of this fungus in South Africa and elsewherein the world.The population of the fungus in South Africa was studied and the 121 isolatescollected were found to belong to 13 different mycelial compatibility groups (MCG),occurring on various crop and other plants in different geographic localities. Vagueassociations between MCG, host plant and geographical area could be observed.The genetic fingerprinting technique of amplified fragment length polymorph ismswas found to be an effective tool to distinguish between MCGs of S. rolfsii. Thistechnique has never before been used for this purpose, even though other genetictechniques have been used in other studies. No previous study, however, was able todistinguish isolates within MCGs, as this study was able to do. The hypothesis was alsomade that isolates within a MCG are not clonally derived, based on the differencesobserved between isolates in the same MCG, the different host plants and the differentgeographic areas from which the isolates originated.The pathogenicity of MCGs of S. rolfsii to groundnut appeared to be significantlydifferent from group to group, but the results of field trials suggested that isolates werenot fixed into specific MCGs, even though a controlled glasshouse experiment did notsupport this. The phenomenon of MCG switching has never been reported for thisfungus, even though it has been recorded for other fungi. Certain isolates alsoappeared to be more pathogenic to groundnut than others. Mycelial compatibility groupE consistently emerged as a virulent pathogen of groundnut. No groups were found toe specific to any of three other crop plants tested.The control of the fungus in groundnut fields was found to be possible with theuse of an inversion plough in trials conducted over two consecutive seasons. Afungicide was identified that suppressed S. folfsii but not Trichoderma harzianum, anaturally occurring biological antagonist of the pathogen in the soil. The application ofthe fungicide difenoconazole at 12.5% of the registered concentration for groundnuts didnot reduce disease in the field. The application of T. harzianum and difenoconazole inthe early stages of groundnut plant development had no effect on yield or diseaseincidence. levels of disease in the field were found to increase with a decreased plantdensity. This observation was attributed to increased soil erosion in the field as a resultof the sparser plant density.Sclerotium roltsii is a virulent pathogen of numerous crop plants in South Africaand this study has provided some answers to questions regarding the biology andcontrol of this fungus. However, much still has to be discovered and may futurescientists find some inspiration from what was done here.Key words: Sclerotium faItsii, southern stem rot, population, mycelial compatibilitygroups, AFlP analysis, pathogenicity, control, inversion plough, integrated pestmanagement.

[发布机构] University of the Free State