J. Agric. Res. & Dev. 10(2). Copy@2011. Faculty of Agriculture, University of Ilorin Trend in the Performance of Five Open Pollinated Maize Varieties (Zea mays L.) for Grain Yield in different Planting Dates and Years in the Southern Guinea Savanna Ecology of Nigeria G. OLAOYE 1 and O.B. BELLO 2 1 Department of Agronomy, University of Ilorin, Ilorin, Nigeria. 2 Department of Biological Sciences, Fountain University, Osogbo, Osun State, Nigeria. ABSTRACT Three drought tolerant and two adapted maize varieties were evaluated at the University of Ilorin Teaching and Research farm in 2002 and 2003 cropping seasons, using monthly plantings between April and August of each year. Year (Y) and planting time (PD) had significant effects on all traits except anthesis-silking interval. Genotypic differences were significant for all the characters except seedling emergence. Effects of Y x PD, G x Y and G x PD interaction were significant for all parameters except ASI. 2003 cropping season was better than 2002 for the expression of grain yield potentials in the varieties cropping seasons. Early plantings resulted in higher grain yields than late. DT-SR-WCO and DT-SR-Y CO that are superior for grain yield can be tested further under farmers’ growing conditions or utiliz ed in the extraction of inbred lines for the development of improved maize varieties for cultivation in the savanna ecologies of Nigeria. Key words: Drought tolerant, Maize varieties INTRODUCTION Tropical maize is mostly associated with low-input environments characterized by water and temperature stress among others (Boyer, 1982). Drought stress in particular, constitutes the most important abiotic stress, which limits maize productivity especially in the sub-Saharan Africa, where annual maize yield losses due to drought stress can be as high as 80% (Kassei, 1997). Since weather and climate act both as resource and constraints to agricultural production, its impact need to be understood in order to alleviate the consequences of global warming (Adetayo et al., 2008). Several studies on the effects of climate change on agricultural yields (Hu et al., 2005; Tao et al., 2006; Lobell and Field, 2007) have also highlighted the vulnerability of crops to current trends in global clomate warming. Improvements and changes in technology and farm management however can serve as adaptive measures that may partially or completely offset the unfavorable effects of climate change on crops. In the southern Guinea savanna (SGS) of Nigeria, drought stress may result either from abrupt cessation of rains soon after crop establishment in the early season,