Diurnal variation of gas exchange, chlorophyll fluorescence, and photosynthetic response of six parental lines of maize released in three eras

Abstract Over the past seven decades, the grain yield of maize (Zea mays L.) has increased continuously in China, mostly due to hybridization innovations, particularly recent genetic improvements in photosynthesis. In order to reveal photosynthetic characters of elite inbred lines in different ears, a field experiment was conducted at the North China Plain of Shandong Province in China. Six parental lines of maize introduced in three eras (the 1960s, 1980s, and 2000s) were investigated diurnal variation of gas exchange, chlorophyll fluorescence, and photosynthetic response characteristic at the grain filling stage. Compared to earlier parental lines, the 2000s parental lines always had higher net photosynthetic rate (Pn) throughout the day, especially at noon, and a mid-day depression in Pn did not occur in all hybrids parental lines. Moreover, the stomatal conductance (Gs) and water use efficiency (WUE) of the 2000s’ lines showed higher value than those of the 1960s’ and 1980s’ lines. The inbred lines differences in photosynthetic parameters were partly owing to their different quantum carboxylation efficiencies and light synthase activities. Simultaneously, the 2000s parental lines exhibited lower light and CO2 compensation points, and their higher apparent quantum yield, and carboxylation efficiency. These suggested that the modern parental lines required lower light intensity and less CO2 to maintain a relatively high photosynthetic capacity, substantially increasing leaf physical quality and stress resistance. It provided crucial information of high photo-efficiency and stress-resistance breeding in maize.