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Shoot Nitrogen Dynamics in Tropical Common Bean

Plant Environment Lab., Dep. of Agric., Univ. of Reading, Cutbush Lane, Shinfield, Reading RG2 9AD, UK
Int. Maize and Wheat Improvement Ctr (CIMMYT), Apdo, Postal 6-641, 06600 México D.F. México

^* Corresponding author.

Photoperiod has substantial effects on phenology in many cultivars of maize (Zea mays L.). This study investigated if photoperiod sensitivity ends at tassel initiation (TI) by considering whether photoperiod influences the duration from TI to tassel emergence (TE). In the first experiment, five diverse cultivars were grown in 12 different controlled environments until TI, and were then transferred to either short (11 h d^–1) or l ong (16-18 h^–1) days. In the second experiment, these five and seven more cultivars were grown in four different controlled environments until TI, and were then transferred to either short or long days. Leaf numbers per plant were influenced by the photo period experienced before TI (P < 0.01), but not thereafter (P > 0.25); the former effect varied considerably among cultivars (P < 0.01). Durations from TI to TE also differed among cultivars (P < 0.01) and were positively correlated with the photo period experienced after TI (P < 0.01); the effect of a 4 to 7 h d^–1 increase varied (P < 0.05) from 0 in some cultivars to > 5 d in others. A significant negative effect of photoperiod before TI on TI to TE duration was also detected (P < 0.01)o This photo periodic response varied among cultivars (P < 0.01) from negligible to a reduction of > 10 d in TI to TE durations for a 5 h d^–1 increase in photo period between sowing and TI. Thus, photo period-sensitive maize cultivars can be affected by photo period after TI in a way that may tend to cancel out the effect on TI to TE duration of the photo period experienced before TI. Assumptions that the photo period experienced after tassel initiation has no effect on the timing of tassel emergence for the purposes of crop modeling or genetic characterization are consequently unlikely to cause serious errors.

Received for publication December 13, 1990.

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