Open Access Maydica 62-2017 Original Paper RECEIVED 9/26/2016 Determinants of drought tolerance at seedling stage in early and extra-early maize hybrids Richard O Akinwale 1 *, Femi E Awosanmi 1 , Olufunmike O Ogunniyi 1 , Abigail O Fado- ju 1 1 Department of Crop Production and Protection, Obafemi Awolowo University, Ile-Ife. Osun State. Nigeria *Corresponding author: E-mail: akinrichie2002@yahoo.com Keywords: biomass, drought, maize, principal component, seedling aspect Introduction Maize (Zea mays L) is ranked second to wheat in world production of cereal crops. It is widely grown throughout the world in a wide range of agro-ecolog- ical environments. Differential demands for maize in different agro-ecologies of West and Central Africa have facilitated the development of maize of different maturity classes, ranging from extra-early maturing, which matures within 85 and 90 days and adaptive to areas of short rainfall duration to extra-late variet- ies which matures in 120 days and above which are suitable for rainforest conditions with heavy and long duration of rainfall. This makes maize a very versa- tile crop and it is rapidly replacing traditional cereals such as sorghum (Sorghum bicolor L Moench) and millet (Pennisetum glaucum L R.Br.), especially in savanna areas with good access to fertilizer inputs and markets (Badu-Apraku and Fakorede, 2003). However, one major production constraint to maize production in sub-Saharan Africa is drought. Drought stress occurs at any period during the growth cycle of maize including seedling establishment, post-emer- gence growth, flowering or reproduction, and grain filling. Although, drought occurring at flowering and grain-filling stages are considered the most critical in maize growth because they cause gross reduction in grain yield. In addition, Moser (2004) found that pre-anthesis drought significantly reduced the num- ber of kernel rows, number of kernels per row, and 1,000-kernel weight while it consistently increased harvest index. Moreso, when drought occurs during the vegetative stage, it affects the length of the inter- nodes by influencing the cell size development and, thus, the capacity for storing assimilates (Denmead and Shaw, 1960). It has also been reported that pro- longed drought at seedling stage causes total crop failure (Edmeades et al, 1989). The rainforest region of Nigeria and by extension, west Africa is characterized by bimodal rainfall pat- tern with peaks at June and September. In every year, rainfall starts with a few irregular and unpredictable showers in February and March. Farmers are not ad- Abstract Adequate knowledge of response of genotypes to stress and identification of important adaptive traits under stress conditions facilitate rapid progress in a breeding program. The objectives of this study were to evaluate the response of early and extra-early maturing maize hybrids to drought stress imposed at seedling with a view to identifying tolerant hybrids for further breeding studies and identify adaptive traits that could be used as selection criteria for tolerant maize genotypes at this growth stage. This study was conducted in the screenhouse in the Faculty of Agriculture, Obafemi Awolowo University, Ile-Ife, Nigeria. Five seedlings each of 15 hybrids each from early- and extra-early-maturity groups were raised in pots and the pots were arranged in a randomized complete block design with three replicates. The experiment was adequately watered for the first seven days and thereafter watering stopped. The plants were observed for 42 days and data were recorded on emergence and other seed- ling traits. Data collected were subjected to analysis of variance, principal component analysis and correlation analysis. Results showed significant difference between maturity groups for root length and significant difference among genotypes within maturity were obtained for total number of leaf shed, moisture content of root, fresh shoot weight, total fresh biomass and seedling aspect, indicating there was wide variability in the response of the genotypes from the different maturity groups for tolerance to drought at seedling stage. Principal component analysis also identified these traits as the primary traits contributing to diversity among the hybrids under induced drought at seedling stage. Results of correlation analysis showed differential association among traits of early and those of extra-early maize, indicating that mechanism of tolerance to drought in the two maize maturity groups are different. It was concluded that early and extra-early maize hybrids responded differently under drought stress imposed at seedling stage and that seedling stage total number of leaf shed, moisture content of root, fresh shoot biomass, and total fresh biomass were important drought adaptive traits and the traits should be included in com- puting base index for selecting drought tolerant maize at seedling stage.