Maize streak virus (MSV) disease, transmitted by leafhoppers (Cicadulina mbila, Naude), and maize downy mildew (DM) disease caused by Peronosclerospora sorghi (Weston and Uppal) Shaw, are major contributing factors to low maize yields in Africa. These two diseases threaten maize production in Mozambique, thus the importance of breeding Mozambican maize varieties that carry resistance to these diseases. Marker-assisted selection (MAS) was employed to pyramid MSV and DM disease resistant genes into a single genetic background through simultaneous selection. Firstly, it was essential to determine the genetic diversity of MSV disease resistance in 25 elite maize inbred lines to aid in the selection of suitable lines for the introgression of the msv1 gene; and subsequently, to introduce the msv1 resistance gene cluster from two inbred lines, CM505 and CML509, which were identified as the ideal parental lines for the introgression of MSV disease resistance into a locally adapted Mozambican inbred line LP23 that had DM background resistance. Pyramiding the resistance genes by the use of simple sequence repeat (SSR) molecular markers to track the MSV gene cluster was investigated in 118 F3 progeny derived from crosses of CML505 x LP23 and CML509 x LP23. High resolution melt (HRM) analysis using the markers umc2228 and bnlg1811 detected 29 MSV resistant lines. At the International Maize and Wheat Improvement Centre (CIMMYT) in Zimbabwe, MSV disease expression of the 118 F3 progeny lines was assessed under artificial inoculation conditions with viruliferous leafhoppers and the effect of the MSV disease on plant height was measured. Thirty-seven family lines exhibited MSV and DM (DM incidence ≤50) disease resistance. Individual plants from a total of 41 progeny lines, that exhibited MSV disease severity ratings of 2.5 or less in both locations within each of the F3 family lines, were selected based on the presence of the msv1 gene based on SSR data, or field DM disease resistance, and were then advanced to the F4 generation to be fixed for use to improve maize hybrids in Mozambique for MSV resistance. Simultaneous trials were run at Chokwe Research Station in Mozambique for MSV and DM disease assessment, under natural and artificial disease infestation, respectively. Thus the MSV and DM genes were effectively pyramided. Lines with both MSV and DM resistance were advanced to the F4 generation and will be fixed for use to improve maize hybrids in Mozambique for MSV and DM resistance, which will have positive implications on food security in Mozambique. This research discusses the results of combined selection with both artificial inoculation and the three selected SSR markers. It was concluded that a conventional maize breeder can successfully use molecular markers to improve selection intensity and maximise genetic gain. / Thesis (M.Sc.Agric)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Quality protein maize (QPM) has high nutritional value, but production is threatened by downy mildew (DM) and maize streak virus disease (MSVD) among other constraints. There are few studies of DM and MSVD resistance in QPM cultivars. The objective of this study was to improve resistance to DM and MSVD in three QPM populations. This was realized through ascertaining farmers’ key production constraints and special preferences for cultivars; determining the utility of recurrent selection method for improvement of three QPM populations (SussumaS2, ZM521Q and Pop62SRQ); and determining grain yield potential. The study was conducted in Mozambique for DM and in Zimbabwe for MSV, during 2003 to 2006. Surveys were conducted in Manica and Angonia districts in Mozambique to ascertain farmers’ perceptions and preferences for maize varieties, especially QPM. Participatory rural appraisal tools that included semi-structured questionnaires and focus group discussions were used to collect data. Results showed that farmers predominantly grew open pollinated varieties and fewer normal maize hybrids (non-QPM), and grain yield was estimated to be very low (0.2 to 0.6 t ha-1). Results showed that drought and insect pests were the dominant constraints to maize productivity in Mozambique, while diseases were ranked third. Downy mildew disease and MSVD were considered to be the most important diseases reducing maize productivity. Farmers also showed high preference for high yielding and early maturity cultivars in all areas. Predominantly, farmers were still using their local landraces because of sweet taste, particularly for home consumption and flint grain for storage. Farmers’ access to improved cultivars was limited due to high seed prices on the local market. Research priorities as perceived by the farmers included breeding for resistance to drought, grain weevils and diseases and sweetness. Generally, farmers showed little knowledge of QPM varieties and the importance of this trait, but they observed that the few QPM varieties they knew had some weaknesses such as poor storability and susceptibility to DM and MSVD which required improvement. These results should be considered in breeding new cultivars, both normal and QPM. To improve DM and MSV disease resistance in QPM varieties, S1 recurrent selection was conducted in three QPM populations, Sussuma, ZM521Q and Pop62SRQ at Umbeluzi Research Station in Mozambique and at CIMMYT-Harare Research Quality protein maize (QPM) has high nutritional value, but production is threatened by downy mildew (DM) and maize streak virus disease (MSVD) among other constraints. There are few studies of DM and MSVD resistance in QPM cultivars. The objective of this study was to improve resistance to DM and MSVD in three QPM populations. This was realized through ascertaining farmers’ key production constraints and special preferences for cultivars; determining the utility of recurrent selection method for improvement of three QPM populations (SussumaS2, ZM521Q and Pop62SRQ); and determining grain yield potential. The study was conducted in Mozambique for DM and in Zimbabwe for MSV, during 2003 to 2006. Surveys were conducted in Manica and Angonia districts in Mozambique to ascertain farmers’ perceptions and preferences for maize varieties, especially QPM. Participatory rural appraisal tools that included semi-structured questionnaires and focus group discussions were used to collect data. Results showed that farmers predominantly grew open pollinated varieties and fewer normal maize hybrids (non-QPM), and grain yield was estimated to be very low (0.2 to 0.6 t ha-1). Results showed that drought and insect pests were the dominant constraints to maize productivity in Mozambique, while diseases were ranked third. Downy mildew disease and MSVD were considered to be the most important diseases reducing maize productivity. Farmers also showed high preference for high yielding and early maturity cultivars in all areas. Predominantly, farmers were still using their local landraces because of sweet taste, particularly for home consumption and flint grain for storage. Farmers’ access to improved cultivars was limited due to high seed prices on the local market. Research priorities as perceived by the farmers included breeding for resistance to drought, grain weevils and diseases and sweetness. Generally, farmers showed little knowledge of QPM varieties and the importance of this trait, but they observed that the few QPM varieties they knew had some weaknesses such as poor storability and susceptibility to DM and MSVD which required improvement. These results should be considered in breeding new cultivars, both normal and QPM. To improve DM and MSV disease resistance in QPM varieties, S1 recurrent selection was conducted in three QPM populations, Sussuma, ZM521Q and Pop62SRQ at Umbeluzi Research Station in Mozambique and at CIMMYT-Harare Research. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.