Photosynthetic Heterosis in Maize

Abstract

Differences in net C02 uptake of single, attached leaves among slngle cros;s F1's of two combinations, parental inbred lines, a varietal cross F1 and parental open-pollinated varieties were observed. Heterozygous types, i, e. single-cross and varietal cross F1's and open-pollinated varieties, showed a definitely higher photosynthetic rate per unit leaf area as compared with inbreds. The photosynthetic rate per unit leaf area (PA) tended to be positively related to the nitrogen, chlorophyll and d, ry matter cc, ntent per unit leaf area. High PA of the heterozygous types was partly attributable to their higher nitrogen, chlorophyll and dry matter content per unit leaf area. Within inbreds as well as within heterozygous types, photosynhtetic rate per unit leaf nitrogen (nitrogen efficiency), the rate per unit chlorophyll (chlorophyll efiiciency) and the rate per unit leaf dry matter (dry matter efficiency) tended to be negatively related to the nitrogen, chlorophyll and the dry matter content per unit leaf area, respectively. Taking this general trend into account, the authors pointed out that the nitrogen, chlorophyll and dry matter efficiencies of the heterozygous types were definitely higher than those of inbreds. High PA of the heterozygous types seems to be primarily related to their high nitrogen, chlorophyll and dry matter efficiencies. High PA of the heterozygous types was closely associated with their high relative growth rate. Estimation of PA with a fcw leaves of a fcw plants may be useful In predicting the hybrid vigor.