Effects of selecting for yield versus yield efficiency on morphological and physiological traits of tropical maize

Summary

Selection criteria to accelerate improvement of tropical maize (Zea mays L.) are needed because resources are limited and foods needs are growing. Yield efficiency (YE) (yield per unit leaf area), the reported grain yield-limiting factor in tropical maize, should be compared with grain yield (GY) (yield per unit land area) as selection criteria for rapid improvement of tropical maize. Selections for GY and for YE were conducted in two open-pollinated tropical maize cultivars that contrasted in morphological and physiological traits. Effectiveness of each selection criterion, changes in morphological and physiological traits, and density responses of synthetics associated with each selection criterion were studied. S₁ lines were extracted in each population and evaluated in their area of adaptation at three locations in Southeastern Zaire during the 1976–77 growing season. The ten high yield-efficient and ten high yielding S₁ lines in each population were separately combined to produce synthetics for high YE and high GY, respectively. The two synthetics selected in each population were compared with their original population at four densities (40 000, 60 000, 80 000 and 100 000 plants/ha) at Kaniama, Shaba, Zaire during 1977–78. Selecting for GY effectively increased GY, but also tended to maintain or increase excessive vegetative growth. Selecting for YE effectively reduced plant vegetative growth in one population and individual leaf size in the other population. It did not increase GY or YE because environmental and genetic factors that operate on YE were confounded. Neither selection criterion improved density tolerance. Maize breeding should emphasize selecting for combined criteria of GY and YE to achieve high GY, high YE, and density tolerance.