Yield performance of disease resistant double top cross maize hybrids adapted to the medium altitude ecology of Western Kenya - Mexico, DF (Mexico) CIMMYT : 2003 - p. 98-99 - Printed
Biotic stresses such as northern leaf blight, caused by Exserohilum turcicum, gray leaf spot (GLS), caused by Cercopspora zea maydis, and maize streak, as well as abiotic stresses like drought and low soil fertility, are the major maize production constraints in the medium altitude moist ecology of western Kenya. Yield losses of 60% due to GLS have been reported in Kenya, although the loss depends on the time of attack. Northern leaf blight can lead to 100% yield loss in susceptible varieties (Odongo 2000). An effective way of combating these stresses is through the use of diverse source germplasm in varietal development, as this helps to pyramid genes for resistance to more than one stress. Ojiem et al. (1996) reported that lack of suitable variety was among the major causes of the gap between farmers' and researchers' maize yields in western Kenya. In this region, seed companies mainly market three-way and double cross hybrids. However, double top cross hybrids are cheaper to produce and are of greater benefit to farmers because they are less sensitive to inbreeding compared to single crosses. There is a need for a breeding strategy to identify single crosses and non-inbred parents with desirable qualities for use in developing double top cross hybrids. The objectives of this study were to: 1) identify high-yielding adapted double top crosses for use in the region; 2) identify heterotic patterns in the parental single crosses to serve as testers in the region; and 3) estimate general combining ability (GCA) of the testers and specific combining ability (SCA) of the single crosses.