The identification of maize lines with contrasting responses to applied nitrogen.

A better understanding of how maize responds to nitrogen (N) supply is required for both economic and environmental purposes. Contrasting genotypes are indispensable for genetic and physiological studies of any trait, and the identification of the response of a range of lines of maize to two N level, was the aim of this work. One S4 and seven S5 lines, originating from two commercial hybrids, were studied for agronomic traits related to nitrogen-use efficiency (NUE). Two field experiments with two levels of N (10 and 110 Kg N/ha in 2000 and 10 and 130 Kg N/ha in 2001) were carried out. In the first experiment, in which the lines 2, 3, 4, 5, 6, 10, 13, and 17 were tested, the N supplied appeared to be excessive because the maize controls and most of the lines did not show an increase in grain yield at the high N level when compared with the low-N treatment in this experiment. The high N level increased the grain yield only in line 2, decreased grain yield in line 13, but increased the chlorophyll content in all lines except line 3. The second experiment, in which the lines 2, 3, 4, 5, 6, and 10 were tested, showed a severe N deficiency because the maize controls and most of the lines exhibited reduction in grain yield at the low N level when compared with the high-N treatment in this experiment. This severe N deficiency caused a reduction in grain yield in lines 2, 3, 5, and 10, prolificacy (ears plant- 1) in lines 2, 3, 4,and 5, grain N content in all lines (except line 10), and total plant N in lines 2, 3, and 5. On the other hand, this severe N deficiency also caused an increase in 100-kernel weight in line 2 and anthesis-silking in lines 3 and 5. The interactive behavior of all the traits cited indicates that they have different genetic controls at each N level. The existence of genotype-environment interaction may mean that the best genotype at a low N level is not the best at a high N level, and that the physiological mechanisms as well the genes required for high performance are to some extent different. These results also demonstrate that the response to N of these traits is under separate controls for each one, because they did not exhibit consistency in the lines tested. The correlations indicated that the anthesis-silking interval and prolificacy were associated more with grain yield at low-N availability, supporting the idea that these traits can be used to select maize tolerant to low-N soils. The contrasting responses to N availability indicate that these lines are important plant materials for use in further studies of NUE