Modern agricultural practices strive for the high density planting. Therefore, maize hybrids developed and released by Pioneer Hi-Bred International from 1930 to 2001 were primarily selected based on their higher yield in such conditions. However, this selection did not only result in higher yield but also in changes in the morphological traits, such as smaller and more erect leaves and enhanced tolerance to abiotic stress generated by dense planting. Few years ago, auxin and light were proposed to play an important role in this process. In the present study, we investigated the changes in the interaction of light and auxin signaling between four old maize hybrids (307, 317, 3306 and 3366) and the modern hybrid 3394. Etiolated seedlings of the modern hybrid displayed shorter stature and reduced sensitivity to exogenous auxin than the old hybrids, however no differences in the seedlings stature were observed when grown in continuous blue or red light. Nevertheless, the auxin-related responses of the modern hybrid were greatly affected under blue light, suggesting a modification of the interaction between light and auxin signaling pathways that has happened during the breeding process. The role of ABP1 in this interaction was investigated and discussed.
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