Breeding of maize for fall armyworm resistance in southern Africa
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Date
2021-07
Authors
Matova, Prince M.
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Journal ISSN
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Publisher
University of the Free State
Abstract
In 2016 sub-Saharan Africa (SSA) was invaded by the transboundary maize-eating pest, fall armyworm [Spodoptera frugiperda (J.E. Smith); FAW]. The pest has threatened food security and livelihoods of the majority of smallholder farmers in the region. The main aim of this study was to investigate the potential of breeding maize with resistance to FAW in southern Africa. The first study aimed to assess the breeding potential of introduced exotic FAW resistant trait donor maize lines with southern Africa germplasm. Thirteen mid-altitude adapted inbred lines were crossed with seven FAW-resistant exotic donor lines, in a line x tester mating scheme that produced 84 F1s which were evaluated together with checks at four locations under natural FAW infestation. The best exotic donor lines with low and negative general combining ability (GCA) effects for foliar FAW damage (FFAWD) resistance scores and good grain yield (GYD) per se performance were CML139, CML67, CML121 and CML345. Local lines that showed similar good attributes were CimExp1, CimExp4, CimExp5, CimExp8 and CimExp10. The best crosses were CimExp1/CML331, CimExp1/CML345, CimExp10/CML331 CimExp5/CML331 and CimExp5/CML345. In the second study, two sets of germplasm (hybrids/OPVs and inbred lines) were evaluated for FAW resistance under managed and natural FAW infestation. The objective was to evaluate commercial and experimental maize hybrids and parental lines cultivated in southern Africa for resistance to FAW. Commercial cultivars were significantly more affected by FAW infestation than experimental hybrids. The introduced FAW-resistant donor lines (CML338, CML67, CML121 and CML334) showed better resistance to FAW damage, individually and in hybrid combinations. Local inbreds, SV1P, CML491 and CML539, also showed good FAW resistance. Husk cover, ear rot, anthesis date and plant height were correlated with FAW resistance. The third study aimed to investigate the stability of grain yield performance and resistance to FAW of resistant maize lines, cultivars and experimental hybrids under natural FAW infestation. The hybrids Mutsa-MN521 and CimExp55/CML334 were the most preferred, combining FAW resistance, adaptation and stability across FAW infested environments. Other acceptable hybrids were 113WH330, Manjanja-MN421, CML338/CML334 and PAN53. The local inbred lines SV1P and CML491 combined adaptability and stable FFAWD resistance across environments. The best exotic donor lines exhibiting stable FAW resistance were CML67, CML346, CML121 and CML338. Harare and Gwebi were identified as the most discriminating sites for GYD performance in hybrids, while Kadoma and Rattray-Arnold Research Stations were the most discriminating environments for FFAWD among inbred lines. The fourth study explored the opportunity of using mutation breeding in maize crop improvement with the intention to enhance genetic diversity and trait performance to combat emerging threats such as FAW. The study determined optimum gamma irradiation doses to use in maize mutation breeding. Doses in the range of 160 gy - 250 gy were recommended for maize inbred lines while 200 - 275 gy were recommended for OPVs. Overall, the study concluded that effective FAW resistance can be attained in southern Africa using local and exotic genetic resources. The study recommends the use of gamma irradiation to broaden genetic diversity for effective selection. Furthermore, doubled haploid technology and the development and validation of markers will hasten genetic gains, increase selection accuracy and reduce linkage drag in breeding for FAW resistance in southern Africa.
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Keywords
Thesis (Ph.D. (Plant Sciences))--University of the Free State, 2021, Exotic lines, Fall armyworm, Gamma irradiation, Local lines, Resistance, Stability, Armyworms -- Seasonal distribution, Pesticide resistance