Grain and floret number in response to photoperiod during stem elongation in fully and slightly vernalized wheats

The manipulation of photoperiod sensitivity during stem elongation (terminal spikelet initiation-anthesis) has been suggested as a means to increase wheat yield, potential. Nevertheless, photoperiod sensitivity and the interaction with vernalization during that phase have not been previously explored under field conditions. Thus, a field study was carried out (i) to assess whether duration of stem elongation is sensitive to photoperiod experienced only during that phase, and if so (ii) to evaluate whether vernalization interacts with this photoperiod response and (iii) to determine if altering duration of stem elongation may influence wheat yield and its components. The experiment was a factorial combination of two vernalization treatments (15 (V-15) or 50 (V-50) days at 4 +/- 1 degreesC and 8 h photoperiod), two photoperiod regimes during stem elongation (natural daylength in the field (NP + 0) and one daylength extension of 6 h (NP + 6)) and three cultivars (Buck Manantial (BM), Eureka Ferrocarril Sur (EFS), and ProINTA Puntal (PP)). The stem elongation phase responded to the actual photoperiod experienced during that phase in the three cultivars, increasing its duration with shorter photoperiod. In the vernalization-sensitive cultivars EFS and PP, plants vernalized 50 days showed greater response to photoperiod than those vernalized 15 days. In the most photoperiod-sensitive cultivar (BM), as duration of stem elongation lengthened by exposure to less inductive photoperiod, a higher number of fertile florets at anthesis was achieved leading to an increased grain number and thereby to a higher wheat yield. These results reinforce the idea that a longer duration of stem elongation may offer an alternative avenue to improve yield potential in wheat. (C) 2002 Elsevier Science B.V. All rights reserved.