Effect of temperature, vernalization and water stress on phyllochron and final main-stem leaf number of HY320 and Neepawa spring wheats

An understanding of the effect of environment on leaf growth is needed to accurately simulate phenological development of a cereal crop. This study was conducted to determine the effect of temperature, cold (vernalization) and water stress on the phyllochron (degree-days leaf −1 ) prior to the terminal spikelet stage and on the final leaf number produced by the main stem (FLN) of two spring wheat varieties (Triticum aestivum L.), Neepawa and HY320, grown on the Canadian prairies. Within each of five day/night temperature regimes (30/25 °C, 24/19 °C, 21/12 °C, 16/7 °C and 7/2 °C, with means of 28 °C, 22 °C, 18 °C, 13 °C and 5 °C, respectively), the varieties were grown under two cold (not vernalized and vernalized) and two water (wet and dry) treatments. Within a given temperature regime, both varieties responded similarly to the cold treatments. Vernalization reduced phyllochron and FLN in all but the lowest temperature regime, where phyllochron increased and FLN was unaffected. When effective, severe water stress increased phyllochron and decreased FLN. HY320 was relatively more affected by vernalization and less affected by severe water stress than Neepawa. For both varieties, phyllochron was curvilinearly related to temperature and increased as temperature increased. The relationships were noticeably altered by vernalization and severe water stress. When not vernalized, FLN for HY320 increased as temperature increased; FLN for Neepawa reached a maximum at 20 °C. When vernalized, FLN was independent of temperature under optimum water; the reduction of FLN by severe water stress increased as temperature increased. The results of this study suggest that the effect of environmental change on both phyllochron and FLN must be accounted for when accurate and reliable modelling of the early development of spring wheat is required.Key words: Spring wheat, phyllochron, leaf number, temperature, water stress, vernalization