DISSECTION OF PHYSIOLOGICAL PROCESSES UNDERLYING GRAIN YIELD IN MAIZE BY EXAMINING GENETIC IMPROVEMENT AND HETEROSIS

Maize (Zea mays L.) grain yield in the USA has increased by about 100 kg ha-1 year-1 or 2% year-1 from the start of large-scale adoption of hybrids by maize growers in the late 1930s until the first decade of the 21st century and about 75% of the yield improvement has been attributed to genetic gain. Yield improvement has been associated with increased stress tolerance and het- erosis, but the nature of the enhanced stress tolerance re- mains...