Advances in Improving Ukiriguru Composite B Maize (Zea mays L.) Variety through S1 Recurrent Selection
S1 recurrent selection was carried out to improve grain yield, plant height, ear placement, resistance to lodging and other desirable agronomic traits in Ukiriguru composite B (UCB) maize variety. This paper presents the genetic gain and progress made in improving these traits through two cycles of selection. Three hundred and sixty, and 254 S1 families were evaluated in three environments and 36 and 25 families were selected following 10% selection intensity during the first (C1) and the second (C2) cycles, respectively. The selected families were recombined in isolated half-sib recombination blocks using remnant seeds. The progress made through selection was determined by evaluating the parent population (UCB C0), the first (UCB S1 C1) and the second (UCB S1 C2) selection cycles in six environments in a randomized complete block design in four replications. Commercial open-pollinated and hybrid varieties were included as checks. UCB S1 C2 produced mean grain yield of 8.7 t ha-1 and had a significant (P < 0.01) genetic gain of 30% (2.0 t ha-1) with mean gain of 15.0% (1.0 t ha-1) cycle-1. The selection also resulted in short plant height and low ear placement with significant (P < 0.01) genetic gain of 9.6% (30.8 cm) and 19.6% (39.6 cm), respectively, and superiority in tolerance to diseases and resistance to lodging. Still selection had significant (P < 0.01) grain yield benefit of 35.0% (3.1 t ha-1) and 29.3% (2.6 t ha-1) relative to Gibe Composite 1 and Kuleni, respectively, and showed comparable yield potential with commercial hybrids, BH660 and BH670. It was concluded that two cycles of S1 recurrent selection have brought significant genetic improvement in grain yield and major agronomic traits in UCB. Hence UCB S1 C2 was fully released and recommended for commercial production in the mid-altitude (1600-1800 masl) agro-ecologies of Jimma and Illu Ababora Zones, and similar areas in the south-western areas of Ethiopia. After release, it was named as ‘Morka’ meaning ‘competent’, to express its yield potential which is comparable to the yield potential of popular hybrid varieties in the zones.
Keywords: Genetic Gain; Morka; Recurrent Selection; Response to Selection; Ukiriguru Composite B