Photosynthetic Heterosis in Maize

Abstract

Differences in net carbon dioxide uptake were studied in single, attached leaves of the parents and F1s of two single interline crosses and one varietal cross. The F1s and the open-pollinated parents clearly showed a higher photosynthetic rate than the inbreds. Photosynthetic rate per unit leaf area tended to be positively related to nitrogen, chlorophyll and dry-matter content per unit leaf area. Within both the inbreds and the heterozygous forms, photosynthetic rate per unit of leaf nitrogen (nitrogen efficiency), per unit of chlorophyll (chlorophyll efficiency) and per unit of leaf dry matter (dry matter efficiency) tended to be negatively related to nitrogen, chlorophyll and dry-matter content per unit leaf area, respectively. The three types of efficiency were clearly higher in the heterozygous forms than in the inbreds. The high photosynthetic rate per unit leaf area seen in the heterozygous forms was closely associated with their high relative growth rate; estimation of this rate using a few leaves from a few plants is suggested for predicting heterosis.