Demand-Driven Technologies for Sustainable Maize ... - IITA

55Eticha et al. 2005). Considerable progress has been made in breedingmaize for acid soil tolerance through recurrent selection (Lima et al.1992; Granados et al. 1993; Ceballos et al. 1995). However, mostof the materials used exhibited signifi cant additive genetic variancex environment interaction, suggesting that the materials had specifi cadaptation (Borrero et al. 1995). Therefore, to identify and improvevarieties that would perform well under acid soil and non-acid soilenvironments, selections would have to be based on performanceacross a range of environments. This would lead to germplasmwith broader adaptation. One way to obtain such germplasm is byintrogression of exotic germplasm to locally adapted cultivars.Heterosis has been reported for grain yield of maize under acidsoil conditions (Lima et al. 1992; Pandey et al. 1994; Ceballos et al.1998). This information led to extensive selection of inbred lines forhybrid development under soil acid conditions (Narro et al. 2000;Thé et al. 2002). In the present study, 15 such inbreds were usedin a diallel cross and the resulting 105 single-cross hybrids wereused to (i) evaluate the genetic potential of introduced inbred linesfor the improvement of acid tolerance in varieties adapted to WCAand (ii) identify high yielding crosses under acid soil conditions. Theinformation obtained on the mode of gene action would assist thebreeder to classify the lines into heterotic pools for better exploitationof heterosis under acid soil conditions.Materials and MethodsFifteen maize inbred lines with different genetic backgrounds werecrossed in a diallel scheme to produce 105 F1 hybrids. The inbredparents included 4 lines introduced from CIMMYT-Colombia (Cml365, Cml 358, Cla 17, Cla 18), 2 inbred lines from CIMMYT-Mexico(Cml 247 and Cml 254), 1 inbred line from IITA-Ibadan (9450), 2lines from IRAD-Cameroon with mid-altitude adaptation (87036,91105) and 3 lines from IRAD-Cameroon with lowland adaptation(Cam inb gp117, NCRE gp28, and ATP S4-25W). The characteristicsof the parental lines are presented in Table 1.The 105 F1 hybrids were evaluated for 2 years at Nkoemvone(Ebolowa, 2° 43’N, 12° 15’E, 637 mas, oxisol, typical Kandidious) in2003 and 2004. The hybrids were tested under two soil treatments:native acid soil with toxic level of Al and non-acid soil, which werelimed plots of native soil. The experimental design was a split-plot withsoil treatment as main plot and hybrids as sub-plot. The hybrids werearranged in a randomized complete block design with 3 replicates.Each experimental unit consisted of a single 5m row, with 0.75mbetween-row spacing. The spacing between maize hills in the samerow was 0.5 m.