Combining ability for yield and yield components of,early maturing prolific maize (Zea mays L.)

Abstract

Eight early maturing inbred lines of maize with prolific potential were crossed in a diallel system (excluding reciprocals) to determine the inheritance and relationship among yield and yield components. The inbred lines also were crossed to four testers in a top cross system. The parents,F1 hybrids,top cross progenies and testers were evaluated during the long rain season at the University of Nairobi, Kabete Field Station and at National Horticultural Research Centre, Thika, in 1991. F heterosis was exhibited by some hybrids for all 1 traits studied. Yield heterosis over the better parent averaged 38.4% at Kabete and 41.5% at Thika. High yielding parents did not necessarily produce high yielding hybrids. However, hybrids yielding better than the high parent had at least one of the yield components higher than the high parent values. Kernel weight appeared to contribute significantly to yield heterosis. Three hybrids; DC22xDC26, DC15xDC22 and DC3xDC5 gave outstanding yields and consistently ranked first, second and third, respectively, at both locations. General and specific combining ability determined by Griffing's method 2, model I analysis were both important for days to flowering, plant height, duration to maturity, kernel row number and kernel weight. Specific combining ability alone was important for ear number, ear length and grain yield. Parent DC5, DC15 and DC37 transmitted earliness; DC22 increased kernel row number; (x) DC15, DC22 and DC37 increased ear length; DC5 and DC22 .increased kernel weight; DC15, DC22 and DC26 higher yields. Grain yield was positively correlated with ear number, kernel row number, 100 kernel weight, ear length and days to flowering. Correlations among yield components were either negative or nonsignificant, except for plant height with ear length and days to flowering, and for 100 kernel weight with ear length at Kabete. These associations ruled out the possibility of indirect selection by use of yield components for improvement of yield. Direct selection for yield is therefore suggested. Top crosses did not perform better than Fl hybrids for important traits such as, ear number, 100 kernel weight and grain yield. However, they underscored the importance of genetic diversity in the expression of heterosis. They particularly excelled in heterotic values for earliness and reduced plant height. Top crosses; 844BxDC26, 573AxDC3, Pop.42xDC3 and Pop.42xDC37 gave significant positive combining ability effects for grain yield. The four testers ranked inbred lines differently at both locations. Single cross and top cross tests identified good/poor general combiners differently and also ranked inbred lines differently at the two locations