Photoperiod during stem elongation in wheat: is its impact on fertile floret and grain number determination similar to that of radiation?

GONZÁLEZ FG, SLAFER GA, MIRALLES DJ

AUSTRALIAN JOURNAL OF PLANT PHYSIOLOGY

Año: 2005 p. 181 - 188

0310-7841

Abstract Increasing duration of stem elongation through short photoperiod would result in higher spike dry weight at anthesis, which is positively associated with the number of fertile florets and grains in wheat. Whether photoperiod effects on fertile florets and grains are only mediated by assimilate supply to the growing spike, however, is not easy to determine when spike weight variation is attained only through photoperiod treatments. This study was aimed to determine whether photoperiod effects on number of fertile florets and grains may not be mediated, at least in part, by assimilate supply, by comparing the magnitude of the effects with that of shading the canopy. The spike dry weight at anthesis was changed through the factorial combination of different photoperiod (NP+0 and NP+6, natural and 6 hours extended photoperiod) and shading (un-shaded and 67±3% shaded) treatments in both cases only during stem elongation of Buck Manantial, a cultivar known for its photoperiod sensitivity in this phase from previous studies. Both treatments modified spike dry weight at anthesis and the number of fertile florets and grains, independently. As duration of stem elongation was lengthened by exposure to natural photoperiod and incident radiation was relatively high, spike dry weight at anthesis increased by 33% (NP+0 vs. NP+6) and 27% (un-shaded vs. shaded), respectively. The number of fertile florets increased similarly to spike dry weight (34% NP+0 vs. NP+6 and 28% un-shaded vs.. shaded) resulting in higher number of grains and yield. Most photoperiod effects on the number of fertile florets and, consequently, on the number of grains, were mediated by assimilate supply to the growing spike as the same relationship between the number of fertile florets and spike dry weight at anthesis was observed for photoperiod and shading treatments (R2 = 0.99, p<0.05).   Keywords: stem elongation, wheat, photoperiod, radiation, fertile floret number, grain number.