Original paper 64 ~ M 27 Open Access Maydica electronic publication - 2019 Maydica Introduction Maize (Zea mays L) is a major cereal crop and an important component of human and animal diets as well as raw material for industry (http://www.iita.org/ maize, USAID/EAT, 2012). In Ghana, maize production is estimated at around 1.79 MT per annum (USAID/ EAT, 2012) from an area of approximately 992,000 ha with yield estimates of about 1.8 ton/ha in farmer fields (MOFA, 2011). This is generally low compared to global average of 4-5 ton/ha and over 8 tons/ha in the United States of America (USA) (FAOSTAT, 2013). This low productivity may be partly attributed to frequent biotic and abiotic stresses including disease outbreaks, drought and poor farming practices (Morris et al., 1999). Other factors include continuous use of unimproved landraces, poor soils and erratic rainfall patterns (Akande and Lamidi, 2006, Bua and Chelimo, 2010, USAID/EAT, 2012). Research efforts have been intensified by Maize breeders in Ghana to develop varieties for improved productivity and with adequate resistance or tolerance to the Maize streak virus disease (MSVD) (Wiredu, 2010; Ragasa et al., 2013). The Maize streak virus (MSV) causes this major foliar disease (Storey, 1925) that affects maize throughout the Sub-Saharan Africa (Pingali and Pandey, 2001). Its prevalence in farmers’ fields has been reported in several regions of Ghana (Oppong et al., 2015). An economic loss of between US $120 – US $480 million based on a conservative yield reduction of about 6% - 10% yearly in Africa has been reported (Martin and Shepherd, 2009). To improve productivity of the crop and management of the disease, the incorporation of landraces and exotic germplasm into breeding programs have been suggested (Carena, 2005, Hallauer and Miranda, 1981, Michelini and Hallauer, 1993, Soengas et al., 2003). Landraces and wild relatives represent an extraordinary genetic resource of maize, with significant allelic diversity, much of which have not been incorporated into improved varieties (Sharma et al., 2010b, Analyzing combining abilities and heterotic groups among Ghanaian maize landraces for yield and resistance/ tolerance to Maize Streak Virus Disease Oppong Allen 1 ,*, Appiah-Kubi David 1 , Ifie E. Beatrice 2 , Abrokwah A. Linda 1 , Ofori Kwadwo 2 , Offei K. Samuel 2 , Adu-Dappah Hans 1 , Mochiah B. Moses 1 , Warburton L. Marilyn 3 1 CSIR—Crops Research Institute, P.O. Box 3785 Kumasi, Ghana. 2 West Africa Centre for Crop Improvement (WACCI), PMB 30, University of Ghana, Legon. Ghana 3 USDA-ARS Corn Host Plant Resistance Research Unit (CHPRRU), PO Box 9555, Mississippi State, 39762, USA * Corresponding Author : E-mail: alnopp@yahoo.co.uk KeyWords: Landraces, hybrid, yield, combining abilities, MSVD. Abstract Maize is an important cereal crop in Ghana. Yields in farmer fields have always been low because of over reliance on unimproved local landraces for cultivation. This study was conducted to determine if the productivity of these landraces can be improved by developing hybrid varieties that combine high yield and resistance to the Maize Streak Virus Disease (MSVD). Seventeen local landrace populations were assembled and then crossed with 5 exotic inbred lines (CML202, CML442, CML444, TZEI 23 and TZEI17). A crossing block using the North Carolina Design II was used to generate F 1 top-cross hybrids which were evaluated in multi-locational trials for two years. GCA, SCA and heterosis were estimated and heterotic groups assigned to the landraces. This study was able to identify high heterosis among some of the top-cross hybrids and assigned some of the landraces into heterotic groups. Highly significant GCA and SCA effects were identified which implies MSVD incidence/resistance as well as yield related traits can be improved. CML442, CML444 and TZEI17 contributed positively to yield increases as well as improved tolerance/resistance to MSVD. Landraces LA3, LA80, LA76, and LA457 displayed highly si- gnificant SCA effects for yield, which suggests dominance and epistatic gene action. The high yielding hybrids identified show that some inbred lines and landraces combinations can contribute to significantly raise farmers’ yields and improve resistance/tolerance to MSVD in Ghanaian environments.