ABSTRACT

Field experiments were conducted at the Teaching and Research Farm of the Department of Crop Science, Faculty of Agriculture, University of Nigeria, Nsukka to commence the process of developing high yielding maize with resistance to stem borers in a humid environment. The specific objectives were to (i) screen some maize genotypes for agronomic traits and stem borer resistance (ii) estimate some genetic parameters of the genotypes studied. Twenty maize genotypes used comprised twelve maize genotypes collected from the International Institute of Tropical Agriculture (IITA) namely (2009 TZE OR1 DT STR QPM (TOR1), AMA TZBR - Y - F2 (AMA), TZBR COMP - 2 - YC1F2 (COMP2), BR 9928 DMRSR (B28), DMR - LSR – Y (DMR), TZE - Y - POP DT STR QPM (POP), 2009 TZE OR2 DT STR QPM (TOR2), 99 TZE Y - STR QPM (99 TZE), BR 9943 DMRSR (B43), TZBR COMP - YC1F2 (COMP1), EV DT - Y - 2000 STR QPM (EVDT) and TZEE - Y - POR STR QPM CO (PORC)) and eight (8) local accessions (Ugwuachara (UG), Umukasi (UM), ORBA1, Obukpa (OB), ORBA2, Edem Ani (EA), Isakpu (IS) and Ajuona (AJ)) from Enugu state, Nigeria. The parameters measured include days to tasselling, silking, maturity, stem girth, number of leaves, ear height, plant height, ear length, ear diameter, number of kernel per row, number of rows per ear, number of kernel per cob, number of ear per plant, shelling percentage, ear weight, grain yield, brown spot disease, lodging incidence, stem borer infestation, number of exit holes and tunnel damage length. General combining ability (GCA) of the parents and specific combining ability (SCA) of the hybrids were estimated using Graffings’ model 1 method 2 in a 10 x 10 diallel cross. Among the parents, POP and PORC had significantly (p < 0.05) shorter days to tasselling (55.67 and 56.00) and silking (57.00 and 58.33), respectively than other genotypes. The parent UG had significantly (p < 0.05) higher ear weight (209.40 g) and grain yield (6.23 ton/ha) among other genotypes. The ORBA2 parents gave significantly (p < 0.05) higher number of kernel per cob (419.50) and hundred grain weights (33.60 g) while the parent UM gave the highest number of ears per plant (1.48). The parent OB obtained the highest stem borer infestation (20 %), number of exit hole (2.83) and tunnel damage length (7.37 cm). Majority of the hybrids produced performed significantly (p < 0.05) higher than the parents in most of the traits. The hybrid UG x ORBA2 had significantly higher ear weight (350 g) and grain yield (11.35 ton/ha). The hybrid UM x B43 obtained significantly higher number of ear per plant (1.83) while UM x OB hybrid gave highest number of kernels per cob (611.30). The hybrid B28 x B43 had highest positive better parent heterosis (BPH) for ear weight (136.56 %) and grain yield (193.83 %). The hybrid UG x B28 (101.16 %) obtained higher BPH on number of kernel per cob while UM x B43 (26.88%) was higher on number of ear per plant. The hybrid PORC x B28 had the least stem borer infestation (6.14 %) while TOR1 x B43 obtained lower number of exit holes (1.00) and tunnel damage length (7.12 cm). The ORBA1 parent was the best combiner among all the parents while POP x PORC was the best combiner among all the hybrids in yield and yield attributes. A cross involving B28 x B43, ORBA1 x B28, ORBA1 x ORBA2, ORBA2 x B43, PORC x B28, TOR1 x B43, TOR1 x POP, TOR1 x PORC, TOR1 x UM, UG x B43, UG x UM, UM x B28, UM x B43 and UM x OB could be resistant to stem borer while a cross involving UG x ORBA2, ORBA2 x B43, ORBA2 x UM, PORC x B43, UG x B43 and UM x B28 could also serve as potential hybrids for improving maize yield.

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INTRODUCTION

Maize (Zea mays L.) belongs to the family of grass Gramineae (Poaceae). It is a tall, monoecious annual plant with male and female flowers in separate places on the same plant with an extensive fibrous root system. Its centre of origin is Mesoamerican region, now Mexico and Central America (Doebley, 1994) and its domestication started at least 6000 years ago. Maize is one of the most productive and widely adapted crop species in the world. It is cultivated in all parts of the world except Antarctica. Loamy or silty loam soil or silty clay loam is the ideal soil type for its cultivation and a pH of 6.5 to 7.5 is the most preferred for its growth. It is among the leading cereal crops after wheat and rice with regard to cultivation area, total production and consumption (Olakojo and Akinlosotu, 2004; CIMMYT, 2004; Olawuyi et al., 2010). Global production amounted to 130 million hactare with output of 574 million metric tons (Ito, 1998).

Maize is an important staple food crop for millions of people both in developed and developing countries. It is relatively high yielding, easy to digest, easily processed and cheaper than other cereals. In Nigeria, maize is used directly for human consumption as well as infant nutrition in the form of porridge during weaning period, without any protein supplement such as egg, meat or beans which are comparatively expensive especially for poor-resource families in the rural areas (Yusuf, 2010). In Africa, maize is consumed as a starchy base in a wide variety of porridges, pastes, grits and beer. Fresh harvested maize is eaten parched, baked, roasted or boiled and plays an important role in filling the hunger gap after dry season. The starch extracted from maize grain is used in making confectionary and noodles. It could be used as feed for livestock and other industrial purposes.

Several breeding methods have been used by maize breeders to develop new cultivars and the choice of a specific breeding method will depend on the type of cultivar. Recurrent selections method has been used for population improvement of maize (Roger et al., 1998; Leta, 2010) with prospect of improving yields and other agronomic traits. The use of phenotypic recurrent selection has been effective in improving characters such as protein, yield, oil, maturity of maize and its cycle can be completed within two years (Obi, 2006). Studies comparing effects of different selection procedures exist in the literature (Ajala et al., 2009) and one could expect 2 to 7% increase per cycles in grain yield depending on the germplasm and selection method (CIMMYT 1981; Darrah, 1986). Breeding for improved varieties requires a thorough