Evaluation of maize breeding populations for resistance to Fusarium verticillioides and fumonisin contamination

Netshifhefhe, Nakisani Elelwani Innocentia (2017-03)

Thesis (MSc)--Stellenbosch University, 2017.

Thesis

ENGLISH SUMMARY: Maize is an important crop cultivated all around the world. It is the main source of carbohydrates for over 200 million people in Sub-Saharan Africa. Daily consumption rates can reach up to 500 g per person in certain regions of Africa. Maize production is threatened by several abiotic and biotic factors which include fungi that cause maize ear rots. Fusarium verticillioides, which causes Fusarium ear rot (FER), and Aspergillus flavus, which causes Aspergillus ear rot (AER), are the most common fungal species associated with maize produced in southern and eastern Africa, respectively. Moreover, F. verticillioides produces fumonisins and A. flavus produces aflatoxins which are toxic secondary metabolites associated with harmful effects on humans and animals. Although several management strategies can be used to reduce mycotoxin accumulation in grain, host resistance has been documented to be the most efficient, cost-effective and environmentally sound strategy to minimize contamination. This study focused on evaluating F1 hybrids for improved resistance to FER and fumonisin contamination under South African and Kenyan conditions. A number of hybrids exhibited improved resistance to FER, fungal and fumonisin contamination. In South Africa, hybrids R119W x CKL05015, CML495 x CKL05015 and CKL05015 x R119W were the most resistant to FER severity, F. verticillioides colonisation and fumonisin contamination, respectively. Under Kenyan conditions, fungal colonisation was lowest in hybrids CKL05015 x CML495 and MIRTC5 x CML495, while fumonisin concentrations were lowest in hybrids CML444 x MIRTC5 and R119W x CKL05015. Parental inbred line performance was indicative of F1 hybrids performance. CIMMYT inbred lines CKL05015 and CML495, previously characterised as resistant to AER, exhibited significant resistance to F. verticillioides and its fumonisins across both countries. These lines were also found to be good general combiners for resistance to fumonisin contamination. Furthermore, F2 populations were also evaluated and the resistant F2 populations identified in this study can be used to produce recombinant inbred lines to utilise in genetic fingerprinting and mapping of resistant genes. Significant genotype x environment interactions influenced FER severity, fungal and fumonisin accumulation in maize grain. General combining ability (GCA) and specific combining ability (SCA) were significant for all three infection parameters evaluated while additive gene effects were predominant in the inheritance of resistance in this set of hybrids. This study provided fundamental information on maize lines that could be used by breeders to develop resistant cultivars. Based on the findings of this study, breeding for resistance to F. verticillioides and its fumonisins should be successful and expedited if the parental material involved is resistant.

AFRIKAANSE OPSOMMING: Mielies is 'n belangrike gewas wat regoor die wêreld verbou word. Dit is die belangrikste bron van koolhidrate vir meer as 200 miljoen mense in Sub-Sahara Afrika. ʼn Daaglikse inname van tot 500 g per persoon is al in sekere streke van Afrika waargeneem. Mielieproduksie word bedreig deur abiotiese en biotiese faktore soos swamme, wat kopvrot van mielies veroorsaak. Fusarium verticillioides, wat Fusarium kopvrot (FKV) veroorsaak, en Aspergillus flavus, wat Aspergillus kopvrot (AKV) veroorsaak, is die mees algemene swamspesies wat met mielies geassosieer word wat onderskeidelik in suider- en oos-Afrika, geproduseer word. Verder, produseer F. verticillioides fumonisiens en A. flavus aflatoksiene wat giftig sekondêre metaboliete is, wat verband hou met skadelike effekte op mens en vee. Hoewel verskeie strategieë gebruik kan word om mikotoksien opeenhoping in graan te verminder, word gasheerweerstand beskou as die mees doeltreffende, koste-effektiewe en omgewingsvriendelike strategie om besoedeling te verminder. Hierdie studie het gefokus op die evaluering van F1 basters vir verbeterde weerstand teen FKV en fumonisien besoedeling in Suid-Afrika en Kenia. 'n Aantal basters het verbeterde weerstand teen FKV, swam- en fumonisien besmetting getoon. In Suid-Afrika het basters R119W x CKL05015, CML495 x CKL05015 en CKL05015 x R119W die meeste weerstand teen FKV, F. verticillioides kolonisasie en fumonisien besmetting, onderskeidelik, getoon. In Kenia was swamkolonisasie die laagste in basters CKL05015 x CML495 en MIRTC5 x CML495, terwyl fumonisien konsentrasies die laagste in basters CML444 x MIRTC5 en R119W x CKL05015 was. Ouerlike inteellyn prestasie was 'n aanduiding van F1 baster prestasie. Keniaanse ingeteelde lyne CKL05015 en CML495, voorheen gekenmerk as weerstandig teen AER, het beduidende weerstand teenoor F. Verticillioides, en sy fumonisien, in albei lande getoon. Hierdie lyne is ook gevind om as goeie algemene kombineerders vir weerstand teen fumonisien besmetting te dien. Verder is F2 bevolkings ook geëvalueer en die weerstandige F2 bevolkings wat in hierdie studie gevind was, kan gebruik word om rekombinante ingeteelde lyne te produseer vir die doel van genetiese vingerafdrukke en kartering van weerstandige gene. Beduidende genotipe x omgewingsinteraksies beïnvloed FKV, swam- en fumonisien opeenhoping in mielie graan. Algemene kombinasie vermoë en spesifieke kombinasie vermoë was betekenisvol vir al drie infeksie parameters geëvalueer; terwyl toevoeging geen effekte oorheersend in die erfenis van weerstand in hierdie stel basters was. Hierdie studie verskaf fundamentele inligting oor mielie-lyne, wat deur telers gebruik kan word om weerstandbiedende kultivars te ontwikkel. Op grond van die bevindinge van hierdie studie, kan die teling vir weerstand teen F. verticillioides en sy fumonisien suksesvol en spoedig wees, as die ouerlike materiaal betrokke, bestand is.

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