MAIZE EAR MOISTURE DURING GRAIN-FILLING, AND ITS RELATION TO PHYSIOLOGICAL MATURITY AND GRAIN-DRYING

Dry-matter and water content of kernels, rachii and ears of maize (Zea mays L.) cultivar Pioneer 3901 were measured during the period from silking to harvest maturity in order to (a) determine when net loss of water from the kernels and ear commenced, (b) investigate the use of ear moisture-content (% wet-weight basis) as a scale for kernel development during grain-filling, and (c) use this scale to investigate the relationships between ear moisture, physiological maturity and the environment. Water loss occurred in two phases. The first phase, ending at physiological maturity, had a constant rate of water loss, and was interpreted as a 'developmental' loss of water associated with grain-filling. The second phase, which commenced at physiological maturity, showed a falling rate of water loss characteristic of the drying process. This pattern of water loss was consistent for 17 other genotypes studied in less detail, with maximum water content of the ear occurring between 80 and 60% ear moisture in all cases. Below 70% ear moisture, dry-weight per kernel increased linearly with decreasing ear moisture, enabling a direct and precise estimate to be made of ear moisture-content at the onset of physiological maturity. This method of analysis proved to be useful for evaluating the influence of the environment on grain-filling in a single cultivar. The relationship between dry-weight per kernel and ear moisture was consistent for ten crops of Pioneer 3901 studied over five seasons, but the stage at which grain-filling ceased varied. In six unstressed crops, physiological maturity was attained at between 41 and 43% ear moisture. In other crops, where cessation of grain-filling was associated with the occurence of air frosts, physiological maturity was attained at ear moistures ranging from 45 to 55%. Ear moisture at physiological maturity was also influenced by genotype, with values ranging from 34.3 to 44.5% for the 18 genotypes studied. Differences in ear moisture at physiological maturity among 12 of these genotypes were associated with different absolute levels of water in the ear during grain-filling. Strategies for lowering grain moisture at harvest through breeding should therefore take account of the absolute levels of water in the ear, as well as the more usual expression of moisture content on a wet-weight basis. © 1990.