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dc.contributor.advisorSwart, W. J.
dc.contributor.advisorMcLaren, N. W.
dc.contributor.authorDitshipi, Phoebe Mbochwa
dc.date.accessioned2017-11-02T08:46:49Z
dc.date.available2017-11-02T08:46:49Z
dc.date.issued2007-02
dc.identifier.urihttp://hdl.handle.net/11660/7392
dc.description.abstractEnglish: This study investigated the interaction between grain sorghum and Fusarium spp. associated with the crop in field soils and on sorghum roots as causal agents of crown and root rot. The effect of disease on plant growth and development was investigated as was the efficiency of various inoculation techniques on disease severity. Factors affecting disease susceptibility such as plant age, soil type, soil moisture, soil pH, soil fertility and possible chemical and bio-control control tactics were also investigated. Fusarium spp. isolated from sorghum roots and field soils at Cedara (Kwazulu- Natal province), Bethlehem (Free State province) and Potchefstroom (North West province) indicated that F. oxysporum, F. solani, F. verticillioides and F. thapsinum were the most frequently recovered species. Other Fusarium spp. recovered were F. equiseti, F. nygamai, F. pseudonygamai, F. proliferatum, F. subglutinans and F. polyphialidicum. The most aggressive spp. were F. equiseti, F. thapsinum and F. solani while F. proliferatum, F. subglutinans, F. Verticillioides and F. nygamai were moderately aggressive and F. oxysporum, F. polyphialidicum and F. pseudonygamai least aggressive. Population densities of Fusarium spp. in field soils and on sorghum roots were affected by genotype resistance and initial inoculum. Population densities were higher for susceptible than for resistant sorghum genotypes. A study on the effect of Fusarium spp. on plant growth and development indicated that shoot and root mass did not always correspond with the severity of the disease. Various inoculation techniques for determining susceptibility of sorghum genotypes to crown and root rot and the virulence of Fusarium species were investigated. Wounding the crown and roots and inoculating them with ground colonized oat seeds and drenching soil with a conidial suspension were both very effective. An inoculum concentration of 1 x 106conidia per ml consistently reproduced the disease on inoculated sorghum plants. Crown and root rot severity increased and plant mass decreased with an increase in inoculum concentration. Sorghum genotypes differed in their level of resistance in accordance with the inoculation techniques used. Plant age was shown to affect resistance with two and four-week-old plants being more susceptible than six-week-old plants. Sources of partial resistance to Fusarium crown and root rot were present in some genotypes. Although immunity to Fusarium crown and root rot was not found, Trichoderma harzianum induced systemic resistance in sorghum through the reduction of crown and root rot severity. Fusarium spp. can survive in a wide range of soil types. Certain soils were suppressive while others were more conducive to crown and root rot development. Soil moisture studies indicated that Fusarium spp. causing crown and root rot can survive over a wide range of soil moisture levels ranging between 25 and 100 percent. Low 25% and high 100% moisture levels were suppressive to crown and root rot severity compared to conducive at 50% and 75%. Soil fertility studies indicated that nitrogen applied at normal and high rates significantly and differentially (by genotype) increased crown and root rot severity. Soil amendments also significantly reduced crown and root rot severity with chicken manure being most effective. Studies on the efficacy of fungicides indicated that four fungicides (carboxin / thiram (Vitavax ®Plus FS), tebuconazole/triflumuron (Raxil® 015 ES), tebuconazole, (Ingwe® 6FS), difenoconazole / metalaxyl-m (Dividend ® 030 FS) and a bio-control agent (Trichoderma harzianum) significantly reduced colonization of seedlings. Fungicides also improved plant growth and development by increasing the shoot mass, root mass and enhancing root health. Major Fusarium spp. responsible for crown and root rot were F. equiseti, F. nygamai, F. oxysporum, F. proliferatum, F. pseudonygamai, F. thapsinum, F. solani, F. subglutinans, and F. verticillioides based on the isolation frequencies and pathogenicity tests results. The present study revealed the wide occurance and distribution of Fusarium spp. associated with crown and root rot of sorghum in South Africa. It is hoped that these findings may motivate more research on variation in virulence of these Fusarium spp. Secondly work on the defense mechanisms present in the sorghum genotypes widely grown in in South Africa need to be evaluated in relation to crown and root rot development. The most useful parameters for assessing the disease would be crown and root rot severity and root mass.en_ZA
dc.description.abstractAfrikaans: Die betrokke studie het die interaksie tussen graansorghum en verskeie gronden wortelgedraagde Fusarium spp., wat as die oorsaak van kroon- en wortelvrot van die gewas beskou word, ondersoek. Die invloed van siekte op plantegroei en ontwikkeling is ondersoek, asook die doeltreffendheid van verskeie inokulasietegnieke op die ergheidsgraad van die siekte. Faktore wat siekteweerstand beïnvloed, soos plantouderdom, grondtipe, grondvog, grond pH, grondvrugbaarheid en moontlike chemiese en biologiese beheertaktieke, is ook ondersoek. Fusarium spp. wat vanuit sorghumwortels en geassosieerde grondmonsters vanaf Cedara (KwaZulu-Natal), Bethlehem (Vrystaat) en Potchefstroom (Noordwes) geïsoleer is het aangetoon dat F. oxysporum, F. solani, F. Verticillioides en F. thapsinum die mees algemeen teenwoordige spesies was. Ander Fusarium spp. uit grond herwin was F. equiseti, F. nygamai, F. pseudonygamai, F. proliferatum, F. subglutinans en F. polyphialidicum. Die mees aggressiewe spesies was F. equiseti, F. thapsinum en F. Solani, terwyl F. proliferatum, F. subglutinans, F. Verticillioides en F. nygamai minder aggressief was en F. oxysporum, F. polyphialidicum en F. pseudonygamai die minste aggressief. Populasiedigthede van Fusarium spp. in grond en op sorghumwortels is deur genotipe-weerstand en aanvanklike hoeveelheid inokulum in die grond beïnvloed. Populasiedigthede was hoër vir vatbare as vir weerstandbiedende sorghum genotipes. ‘n Studie op die effek van Fusarium spp. op plantegroei en ontwikkeling het aangetoon dat stingel- en wortelmassa nie voortdurend met siektegraad gekorreleerd was nie. Verskeie inokulasietegnieke om die vatbaarheid van sorghum genotipes teen kroon- en wortelvrot te bepaal, asook die virulensie van sekere Fusarium spp., is ondersoek. Verwonding van die kroon en wortels, gevolg deur inokulasie met gemaalde gekoloniseerde hawersaad en die deurdrenking van plantgrondmedia met ‘n spoorsuspensie, was albei effektief. ‘n Inokulumkonsentrasie van 1 x 106 konidia per ml het voortdurend die siekte op geïnokuleerde sorghumplante geïnisieer. Die graad van kroon- en wortelvrot het toegeneem en plantmassa het afgeneem met toenemende inokulumkonsentrasie. Sorghum genotipes het verskil in hul vlak van weerstand na aanleiding van die inokulasietegniek wat gebruik is. Dit is bewys dat plantouderdom siekteweerstand beïnvloed en dat twee- en vier-weekoue plante meer vatbaar is as ses-week-oue plante. Bronne van gedeeltelike weerstand teen Fusarium kroon en wortelvrot was in sommige genotipes teenwoordig. Alhoewel immuniteit teen die siektes nie gevind is nie, het Trichoderma harzianum sistemiese weerstand geinduseer deur ‘n afname in die intensiteit van die siektes. Fusarium spp. kan in ‘n wye verskeidenheid grondsoorte oorleef. Sekere gronde was onderdrukkend teenoor kroon en wortelvrot, terwyl ander die ontwikkeling van die siekte bevoordeel het. Grondvog studies het aangetoon dat Fusarium spp. wat kroon en wortelvrot veroorsaak oor ‘n wye verskeidenheid grondvogvlakke tussen 25-100% kan oorleef. Baie lae (25%) en baie hoë (100%) vogvlakke het die intensiteit van kroon en wortelvrot onderdruk in vergelyking met middelmatige grondvogvlakke van 50-75% wat dit laat toeneem het. Grondvrugbaarheidstudies het aangetoon dat stikstoftoediening teen normale en hoë peile die intensiteit van kroon- en wortelvrot beduidend en differensieël (volgens genotipe) laat toeneem het. Grondtoevoegings het kroon- en wortelvrot beduidend laat afneem, met hoendermis as die mees effektiefste middel. Studies op die doeltreffendheid van swamdoders het aangetoon dat vier fungisiedes, naamlik carboxin/thiram (Vitavax ®Plus FS), tebuconazole/triflumuron) (Raxil® 015 ES), tebuconazole, (Ingwe® 6FS), difenoconazole/metalaxyl-m (Dividend ® 030 FS) en ‘n bio-beheer agent (Trichoderma harzianum) die kolonisasie van saailinge aansienlik verminder het. Fungisiedes het ook plantegroei en -ontwikkeling bevorder deur stingelen wortelmassa te vermeerder en wortelgesondheid in die algemeen te verbeter.af
dc.description.sponsorshipINTORMIL (USAID)en_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectSorghum -- Diseases and pests -- South Africaen_ZA
dc.subjectFusarium diseases of plants -- South Africaen_ZA
dc.subjectRoot rots -- South Africa -- Etiologyen_ZA
dc.subjectThesis (Ph.D. (Plant Sciences (Centre for Plant Health Management))--University of the Free State, 2007en_ZA
dc.titleEtiology of Fusarium crown and root rot of grain sorghum in South Africaen_ZA
dc.typeThesisen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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