PHYLLOCHRON RESPONSE TO VERNALIZATION AND PHOTOPERIOD IN SPRING WHEAT

An understanding of how environment controls the initiation and develo pment of the leaf is required to construct dynamic crop simulation mod els. The aim of this study was to determine the effect of vernalizatio n and photoperiod on total number of leaves at anthesis, leaf emergenc e rate, and phyllochron in 20 spring wheat genotypes (Triticum aestivu m L.). An experiment was conducted under greenhouse conditions during spring 1992 at ICARDA, Tel Hadya, Syria, with all combinations of thre e photoperiods (8-, 12-, and 16-h daylength) and two vernalization tre atments (vernalized and nonvernalized). Total number of leaves on the main stem at anthesis decreased with increasing photoperiod. Vernaliza tion reduced the total number of leaves on main stem at anthesis in th e eight vernalization-sensitive genotypes. Leaf number on the main ste m was linearly (r = 0.99) related to accumulated growing degree days ( degrees C d), Genotypes differed in leaf emergence rates. Leaf-emergen ce rate increased with increasing photoperiod, Phyllochron decreased w ith increased daylength from 124 degrees C d leaf(-1) at 8 h to 97 deg rees C d leaf(-1) at 16-h photoperiod. These results suggests that, to model leaf appearance and canopy development in wheat, genotypic coef ficients of phyllochron need to be determined in relation to photoperi od, Additionally, the effect of vernalization at inductive photoperiod s on the phyllochron in genotypes adapted to heat-prone tropical envir onments needs further study.