Selection for Differential Productivity Among Juvenile Maize Plants: Associated Net Photosynthetic Rate and Leaf Area Changes1

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Genetic divergence among juvenile maize (Zea mays L.) plants was obtained and evaluated after 6 cycles of selection for high and low stalk volume within the ‘Jarvis’ population. Similar results were obtained for two‐replicate‐selection groups. Selection process modified stalk and leaf production primarily and root production secondarily. Net photosynthetic rates as measured were not associated with differential productivity except in an inverse sense. The principal correlated response to selection was leaf area. In addition to 30% greater leaf area, the high selections had lower chlorophyll level, percent dry matter, net photosynthetic rate, respiration rate, and Hill reaction rate as compared to the low selections. The higher net photosynthetic rates for the low selections, as compared to the highs, held for environmental conditions resulting in low or high photosynthetic rates. The data supported the principal hypothesis for this study that variation in net photosynthetic rates did not play a major role in determining differential productivity within the adapted population. The primary genetic control for productivity in this population appeared to involve the genetics of systems other than photosynthetic.