Delayed flowering time when combining warm temperature and short days in barley

Time to flowering results from the interaction between genotypic and environmental factors. In a field study, flowering of spring barley was delayed in a warmer growing season, particularly in an early sowing under short photoperiod. In order to test differences whether these barleys were sensitive of vernalisation or the delayed flowering uncovered a complex photoperiod x temperature interaction, we carried out two experiment (one in chambers and the other outdoors) with barley cultivars that had exhibited that behaviour and known to possess different sensitivity to photoperiod under cool (12 °C) and warm (19 °C) temperatures and short or extremely long photoperiod after having been vernalised or not. None of the cultivars exhibited any response to vernalisation. All plants developed normally until the onset of stem elongation, but then many of those growing under warm temperatures and short photoperiod failed to flower or had abnormal development. Under short days, warmer temperatures delayed flowering in the insensitive cultivar and did not advance it in the sensitive cultivar. Duration of the construction phase of stem elongation explained better time to flowering than the foundation phase. Both final number of leaves and phyllochron were correlated with time to flowering, but the effects of final leaf number seem to be more decisive than phyllochron in determining the responses of time to flowering.