A host-pathogen study of Fusarium Verticillioides in resistant and susceptible maize inbred lines

Vermeulen, Meagan (2015-03)

Thesis (MSc)--Stellenbosch University, 2015

Thesis

ENGLISH ABSTRACT: Maize (Zea mays L.) is an important crop worldwide and forms the staple diet of many African countries including South Africa. Fusarium ear rot (FER) of maize is caused by a fungus, Fusarium verticillioides, which also produces the fumonisin mycotoxin group. The consumption of fumonisin contaminated maize grain has been associated with serious human and animal health complications. Several South African maize inbred lines exhibiting resistance to FER and fumonisin contamination have been identified. These locally adapted inbred lines could be used to generate mapping populations to identify QTLs associated with resistance to FER and fumonisin contamination. The corresponding markers could be utilised in breeding programmes through marker-assisted selection to ensure the development of commercial cultivars with resistance to FER and fumonisin contamination. In this study, resistant and susceptible maize inbred lines were utilised to commence the development of recombinant inbred line (RIL) populations for the mapping and validation of QTLs associated with FER and fumonisin resistance. One F2 population was phenotypically and genotypically analysed to produce a linkage map for the preliminary identification of QTLs associated with resistance to F. verticillioides infection and fumonisin deposition. A potential QTL for resistance to FER was detected and should be validated across several locations and years in the subsequent RIL population. Additionally, potential resistance barriers of maize to infection by F. verticillioides were investigated by histological studies. The importance of a closed stylar canal in determining resistance to FER was established for nine South African maize inbred lines by means of scanning electron microscopy (SEM). No significant association was observed between a closed stylar canal and the resistance/susceptible status of maize inbred lines before pollination, while the canals appeared closed in all inbred lines following pollination. The results suggest that the stylar canal architecture is not an essential factor determining resistance to F. verticillioides ingress in the maize inbred lines selected for this study. Furthermore, the possibility of resistance to FER and fumonisin contamination being initiated during the seedlings phase of a resistant and susceptible maize inbred line was investigated by means of confocal laser scanning microscopy (CLSM). Fusarium verticillioides growth originating from soil-borne or seed-borne contamination was monitored in various above and below soil plant tissues but no significant difference in the colonisation could be determined between resistant and susceptible maize seedlings. No fumonisin was produced regardless of the inoculation method or resistance status of the plant. These results suggests that the resistant and susceptible maize seedlings used in this study may not be resistant to systemic fungal ingress but may resist the deposition of fumonisins. The resistance associated with the resistant inbred line is not mediated during the seedling phase but potentially through structural and biochemical defence mechanisms during later plant developmental stages.

AFRIKAANSE OPSOMMING: Mielies (Zea mays L.) is ‘n belangrike graangewas wat wêreldwyd geproduseer word en dien as stapelvoedsel in talle Afrika-lande, insluitend Suid-Afrika. Fusarium kopvrot (FKV) in mielies word veroorsaak deur die swam, Fusarium verticillioides, wat ook die fumonisien mikotoksien groepe produseer. Die inname van fumonisien-geïnfekteerde mielies gaan gepaard met ernstige gesondheidsprobleme in mense en diere. Verskeie Suid-Afrikaanse ingeteelde mielielyne, wat weerstandbiedend is teen FKV en fumonisien kontaminasie, is voorheen identifiseer. Hierdie plaaslik-aangepaste teellyne kan gebruik word om kartering populasies te genereer om kwantitatiewe eienskap loci (KEL) te identifiseer wat verband hou met weerstandbiedenheid teen FKV en fumonisien kontaminasie. Die ooreenstemmende merkers kan gebruik word in teelprogramme deur gebruik te maak van merker-geassisteerde seleksie om kommersieële kultivars, wat weerstandbiedend is teenoor FKV en fumonisien kontaminasie, te ontwikkel. In hierdie studie is weerstandbiedende en vatbare mielie inteellyne gebruik om rekombinante inteellyn (RIL) populasies te begin ontwikkel vir die kartering en validasie van KEL’e geassosieer met FKV en fumonisien weerstandbiedenheid. Een F2 populasie was fenotipies en genotipies geanaliseer om ‘n koppeling-kaart te verwek vir die voorlopige identifikasie van KEL’e geassosieer met weerstandigheid tot F. verticillioides infeksie en fumonisein afsetting. ‘n Potensiële KEL vir weerstandbiedenheid is geïdentifiseer, wat verdere bevestiging in die daaropvolgende RIL populasie in verskeie geografiese areas en oor addisionele seisoene, benodig. Potensiële fisiese versperrings teen F. verticillioides tydens mieliesaad infeksie is ook ondersoek met behulp van histologiese studies. Die belangrikheid van ‘n geslote styl-kanaal vir weerstandbiedendheid teenoor FKV is bevestig in nege Suid-Afrikaanse inteellyne deur middel van skandeer elektron mikroskopie (SEM). Geen beduidende verwandskap tussen ‘n geslote styl-kanaal en die weerstandbiedenheid/vatbaarheid van die inteellyne voor bestuiwing is gevind nie, terwyl die kanaal in alle inteellyne gesluit was na bestuiwing. Die resultate dui daarop dat die styl-kanaal argitektuur nie ‘n noodsaaklike faktor is in die bepaling van weestand tot F. verticillioides besmetting in die suiwer mielielyne wat geselekteer was in hierdie studie nie. Verder is die moontlikheid dat weestand tot FKV en fumonisien kontaminasie geïnisieer kan word gedurende die saailing-fase ondersoek in beide ‘n weerstandbiedende en vatbare mielie inteellyn met behulp van konfokale laser skandering mikroskopie (CLSM). Die groei van F. verticillioides afkomstig vanuit die grond of saad is gemonitor in verskeie bo- en ondergrondse plantweefsels, maar geen beduidende verskille in kolonisasie kon opgespoor word tussen weerstandbiedende en vatbare mielie saailinge nie. Geen fumonisien produksie is waargeneem nie, ongeag die innokulasie metode of weerstand-status van die plant. Hierdie resultate dui daarop dat die weerstandbiedende en vatbare mielie saailinge wat in hierdie studie gebruik is moontlik nie weerstandbiedend is teen sistemiese swaminfeksie nie, maar wel weerstand kan bied tot afsetting van fumonisiene. Die weerstand geassosieër met die weerstandbiedende inteellyn word nie bemiddel gedurende die saailingfase nie maar waarskynlik deur strukturele en biochemiese verdedigingsmeganismes tydens latere plant ontwikkelings-stadia.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/96915
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