The phyllochron is a measure of rate of development of plant leaves. Knowledge of the phyllochron for crop species is useful in formulating simulation models and for tracking plant development to determine when to apply management practices that depend on crop development stage. Our objectives were to determine the phyllochron and genetic effects among cultivars of hard red spring wheat (Triticum aestivum L.), durum wheat (T. durum Desf.), and spring barley (Hordeum vulgare L.) and among and within species of crested wheatgrass [Agropyron desertorum (Fischer ex Link) Schultes], western wheatgrass [Elymus smithii (Rybd.) Gould], intermediate wheatgrass [Elytrigia intermedia (Host) Nevski:Syn:A. intermedium (Host) Beauv.], and reed canarygrass (Phalaris arundinacea L.). Phyllochrons for all cultivars of hard red spring wheat, durum wheat, and spring barley averaged 76.9,79.6, and 77.2 growing degree days (GDD) per leaf, respectively. The range in phyllochron among cultivars of hard red spring wheat, durum wheat, and spring barley was 11.2, 5.1, and 9.8 GDD, respectively. Among forage grasses, the phyllochron was 90, 99, 119, and 139 GDD for reed canarygrass, crested wheatgrass, intermediate wheatgrass, and western wheatgrass, respectively. Phyllochron differences among clones within crested wheatgrass cultivar Summit was 21 GDD and within cultivar Nordan was 17 GDD. Specific genetic factors influencing the phyllochron of the species studied were not identified. However, variation among cultivars within species and variation among clones within heterogeneous cultivars suggest that genetic expression should be considered in evaluating the phyllochron for each species.
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