Final kernel number in maize (Zea mays L.) is closely associated with the physiological condition of the crop during the critical period bracketing silking. The objective of this study was to determine whether there is a common underlying relationship between kernel number per plant (KNP) and plant growth rate (PGR) during that critical period when plant growth varies because of different abiotic stresses. A relationship between KNP and PGR obtained from a previous study of variation in plant density and incident radiation was used as reference. KNP and PGR were measured in experiments in which incident radiation per plant, nitrogen (N), and water availabilities were the experimental sources of variation. The equation fitted to the data obtained at different radiation levels explained 72% of the variation in the data obtained at different levels of N or water availability. Moreover, different models for each set of data did not provide a significantly better fit than a single model for the two sets of data combined. A common relationship between KNP and PGR was also obtained when N supply and water availability were variable. The relationship between KNP and PGR obtained for treatments in which PGR was varied through plant density and shading also could predict KNP for conditions in which PGR was affected by water and/or N deficiencies. The PGR during the critical period of kernel set is a good predictor of the capacity of the maize plant to set kernels under a wide range of environmental and management practices.
The length of the growing cycle is one of the most important traits determining hybrid adaptability to the environment. The objective of this work was to study the development, dry matter accumulation, grain yield, harvest index, and sink-source relationship of 11 maize (Zea mays L.) hybrids with contrasting maturity. The durations of the cycle from emergence to flowering varied from 537 to 781 growing degree days and from emergence to physiological maturity from 1221 to 1656掳Cd. Cumulative biomass from emergence to flowering increased linearly with hybrid cycle length. Long-season hybrids showed the highest cumulative interception but the lowest radiation use efficiency (RUE) during reproductive growth. Total aboveground biomass increased from 1624 to 2422 g m 22 with hybrid maturity class, and grain yields were lowest for short-season hybrids (832 g m 22 ) and similar between mid and long-season hybrids (avg. 5 1256 g m 22 ). Increases in maturity class were associated with increases in grain number (from 2432 to 5078 grains m 22 ) and reductions in individual grain growth rate (from 9.1 to 4.9 mg grain 21 d 21 ). The sink-source relationship and the apparent reserve remobilization increased with hybrid maturity class. These results indicate that grain yield of shortseason hybrids would be more limited by the capacity of the reproductive sinks during grain filling than their long-season counterparts. Hybrids Ax 840 and Experimental have a short developmental time from emergence to flowering but a long developmental time from flowering to physiological maturity. This resulted in the largest values of radiation interception during reproductive growth and in the greatest grain yields and harvest indexes.
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