Journal of Agricultural Science; Vol. 11, No. 5; 2019 ISSN 1916-9752 E-ISSN 1916-9760 Published by Canadian Center of Science and Education 47 Distribution of Common Maize Diseases and Molecular Characterization of Maize Streak Virus in Kenya Alice K. Charles 1 , William M. Muiru 1 , Douglas W. Miano 1 & John W. Kimenju 1 1 Department of Plant Science and Crop Protection, University of Nairobi, Nairobi, Kenya Correspondence: Alice K. Charles, Department of Plant Science and Crop Protection, University of Nairobi, Nairobi, Kenya. E-mail: kainyuwatuku@gmail.com Received: April 20, 2018 Accepted: January 27, 2019 Online Published: April 15, 2019 doi:10.5539/jas.v11n4p47 URL: https://doi.org/10.5539/jas.v11n4p47 Abstract Maize is an important food crop in Kenya and is susceptible to a wide range of diseases. A survey was conducted in 2012 in different agro-ecological zones (AEZ) of Kiambu, Embu and Nakuru counties to determine the distribution of northern leaf blight (NLB), common rust (CR), maize streak disease (MSD), gray leaf spot (GLS), head smut (HS) and common smut (CS). Data collected included prevalence, incidence and severity of each of the diseases. Maize leaf samples infected with MSD were also collected for molecular characterization of Maize streak virus (MSV). Northern leaf blight was reported in all counties surveyed with 100% disease prevalence. Kiambu had the highest incidence (100%) of CR whereas Embu had the highest prevalence (45%) of MSD. The incidences of GLS and HS were very low with averages of below 2.5%. The highest incidence of GLS was in Kiambu (5%). High altitude areas had higher incidences of NLB and GLS while CS and MSD were widespread in the three counties. Comparison of 797 nucleotides from the open reading frame (ORF) C2/C1 of MSV with other sequences from the GenBank showed sequence similarities of 99 to 100% with MSV-A strain. The study revealed that the major foliar diseases of maize are widespread in Kenya and therefore there is need to institute measures to manage these diseases and reduce associated losses. Also, the high percent sequence similarities of MSV indicate low variability which is good for breeders since developed resistant varieties can be adopted over a wider region. Keywords: disease incidence, disease severity, diversity, occurrence 1. Introduction Maize (Zea mays L.) is a major cereal crop in the world and ranks third in production after wheat and rice (Muiru et al., 2010; Keya & Rubaihayo, 2013). Maize is important as a staple food in sub-Saharan Africa (SSA), providing food and income to over 300 million resource-poor smallholder farmers (Tefera et al., 2011). The crop provides high yields per unit of land, making it a key crop in ensuring food availability and security for the consumers (Mboya et al., 2011). Maize is a major staple food in Kenya and is used as a determinant of food security (Tumusiime et al., 2010; Ouma & De-Groote, 2011). Maize production in Kenya is constrained by both abiotic and biotic factors (Wambugu & Wafula, 2000). Maximum crop production in the country in a good season is about 34 million tons and it can drop to 18 million tons during drought years (EPZA, 2005). Gray leaf spot (GLS) caused by Cercospora-zeae maydis, common rust (CR) caused by Puccinia sorghi, northern leaf blight (NLB) caused by Exserohilum turcicum and maize streak disease (MSD) caused by Maize streak virus (MSV) are the most important maize diseases in Kenya (Mwangi, 1998; Muiru, 2008; Kinyua et al., 2010). Yield losses due to GLS range from 10 to 70% though during epidemics, 90 to 100% losses have been reported (Nzuve et al., 2013). Maize lethal necrosis (MLN) disease, which is a relatively new disease in the region, has proved to be a major limiting factor in maize production (Wangai et al., 2012). Increased severity of maize diseases in Africa is associated with continuous cultivation and use of susceptible maize cultivars (Danson et al., 2008). Apart from MLN disease which has been extensively studied because of being new in the region, all other maize diseases have received very little attention. Maize streak disease causes yield losses that range from trace to almost 100% (Kyetere et al., 1999; Alegbejo et al., 2002). The disease is distributed throughout the African continent and surrounding islands (Monjane et al., 2011) and is one of the most economically significant member of the Geminiviridae family (Bosque-Perez, 2000). Globally MSD is regarded as the third most serious disease of maize after NLB and GLS (Pratt & Gordon,