Journal of Agricultural Science; Vol. 10, No. 12; 2018 ISSN 1916-9752 E-ISSN 1916-9760 Published by Canadian Center of Science and Education 54 Genotypic Performance of Short-Day Runner Bean (Phaseolus coccineus L.) Lines Combining High Grain Yield and Disease Resistance Mable M. Mulanya 1 , Paul M. Kimani 1 & Rama D. Narla 1 1 Department of Plant Science and Crop Protection, College of Agriculture and Veterinary Sciences, University of Nairobi, Kenya Correspondence: Mable M. Mulanya, Department of Plant Science and Crop Protection, College of Agriculture and Veterinary Sciences, University of Nairobi, Kenya. Tel: 254-721-114-490. E-mail: mulasco@gmail.com Received: August 14, 2018 Accepted: September 30, 2018 Online Published: November 15, 2018 doi:10.5539/jas.v10n12p54 URL: https://doi.org/10.5539/jas.v10n12p54 Abstract Runner bean (Phaseolus coccineus L.) offers a great potential as a grain legume in Africa. However, its productivity is low because no improved short-day varieties are available. The aim of this study was to evaluate advanced short-day runner bean lines for high grain yield, resistance to diseases and suitable for cultivation under tropical conditions. F 6.8 recombinant inbred lines developed from crosses between local landraces and high yielding imported variety (White Emergo) were evaluated in 2013 and 2014 in a randomized complete block design with three replicates at Kabete (1860 m.a.s.l.) and Ol Joro-Orok (2300 m.a.s.l.) in Kenya. Four local runner bean landraces were used as checks. Analysis of variance showed that there were significant differences for days to flowering, response to diseases and grain yield among the evaluated lines. Improved lines flowered within 49 to 52 days in 2013 and 34 to 58 days in 2014.The improved lines flowered earlier at Kabete than Ol Joro-Orok and showed a higher degree of resistance (scores 1-3) to the major diseases rust, bean common mosaic virus (BCMV) and powdery mildew. The mean grain yield at Kabete was 4,426 kg ha -1 compared to 6,523 kg ha -1 at Ol Joro-Orok giving an average yield advantage of up to 67% compared with local short-day landraces. The results indicated that new high yielding short-day runner bean varieties with resistance to major diseases and tropical adaptation can be obtained from these lines. Keywords: runner bean, disease resistance, high yield, tropical adaptation 1. Introduction Grain legumes are rich in dietary protein hence compliment nutritional value of cereals. In the tropics, there has been a need to intensify productivity of other legumes to enhance food security (Wanjekeche et al., 1997). Runner bean is one of the cultivated Phaseolus species which offers a great opportunity as a grain legume in Africa. Runner bean (Phaseolus coccineus L.) has been cultivated since 9000-7000 BC (Smart, 1976), in the region surrounded by Mexican mountains—Puebla, Oaxaca and Chiapas states. In Kenya, the grain runner bean is traditionally grown at elevations between 2000 and 2500 meters above sea level (m.a.s.l.) in Nakuru and Nyandarua Counties. Based on (Kahuro, 1990; Suttie, 1969), the commonly grown variety in these counties is white seeded commonly referred to as ‘butter bean. This is despite the fact that runner bean has other different grain colours ranging from black, white, cream, brown or pink to purple speckled or mottled in the country. The white seeded variety is also grown in South Africa (Brink, 2006). Runner bean is mainly grown both for dry grain and immature green pods as vegetable and can be of bush type or climbing. As a vegetable, the green pods can be harvested in 80 to 90 days from planting, and 100-120 days for dry grain depending on the climatic adaptations (Purseglove, 1987). Despite its importance, grain yield of runner bean in Kenya is as low as 900 to1100 kg ha -1 , estimated 27 years ago (Kahuro, 1990). Current production statistics in the country or region on the grain yield of runner bean are scanty mainly due to underutilization of this type of bean as a commercial crop. The white seeded Kenyan variety flowers and sets pods easily but has poor yields (Kahuro, 1990; Kay, 1981). Due to the out-crossing nature of runner beans in addition to lack of certified seed, most farmers have not been able to maintain a pure stock of seeds, resulting in mixed seeds. Therefore, there is a need of developing improved, pure stands and certified seed for commercial production of runner beans. Most breeding work in Kenya for the last three decades has been focused on common beans and other legumes (Kimani et al., 2009). Until recently, runner