Iranian Society of Weed Science Iranian Journal of Weed Science 1735-3548 9 2 2013 12 22 Modeling the Germination Responses of Wild Barley (Hordeum spontaneum) and Littleseed CannaryGrass (Phalaris minor) to Temperature Modeling the Germination Responses of Wild Barley (Hordeum spontaneum) and Littleseed CannaryGrass (Phalaris minor) to Temperature 105 118 5755 FA Mohsen Beheshtian Hamid Rahimain Hassan Alizadeh Sara Ohadi Ahmad Zare Journal Article 2014 06 02 Different models have been developed to describe the germination responses of seeds to temperature among which the thermal time (heat unit) model has received the greatest implications. Although biologically relevant, the thermal time model is confined to some assumptions which may not be met in some species (particularly in weed species) and thus can result in poor predictions. In this paper we address a novel Weibull-based model which is not only more biologically relevant but also provides the better predictions of germination compared to the conventional model. Therefore, in a laboratory experiment the seed germination of wild barley (<em>Hordeum spontaneum</em>) and little canary grass (<em>Phalaris minor</em>) was tested at various sub- and super-optimal temperatures including 8, 12, 16, 20, 24 and 28 ^oC. The both models were then fitted to the data and compared. The conventional thermal time model provided very poor fits to the germination data of both (particularly <em>P. minor</em>) (RMSE = 9% to 12%). However, the new model well fitted to the same datasets with only 4% error (i.e. RMSE). The Weibull-based model was also good at estimating the germination lag, germination rate and final percent germination in either of weeds studied. Separating the effect of temperature on germination rate and germination extent is suggested to be amongst the most significant ecological properties of the model. For example, the optimum temperature for the mid germination rate (21.8 ^oC in <em>H. spontaneum</em>  and 23.5 ^oC in <em>P. minor</em>) was found to be higher than and beyond the optimum range of germination extent (7.5 to 20 ^oC in <em>H. spontaneum</em>  and 7.5 to 16 ^oC in <em>P. minor</em>). This can give the two species a high degree of germination plasticity in response to the environmental temperatures.   Different models have been developed to describe the germination responses of seeds to temperature among which the thermal time (heat unit) model has received the greatest implications. Although biologically relevant, the thermal time model is confined to some assumptions which may not be met in some species (particularly in weed species) and thus can result in poor predictions. In this paper we address a novel Weibull-based model which is not only more biologically relevant but also provides the better predictions of germination compared to the conventional model. Therefore, in a laboratory experiment the seed germination of wild barley (<em>Hordeum spontaneum</em>) and little canary grass (<em>Phalaris minor</em>) was tested at various sub- and super-optimal temperatures including 8, 12, 16, 20, 24 and 28 ^oC. The both models were then fitted to the data and compared. The conventional thermal time model provided very poor fits to the germination data of both (particularly <em>P. minor</em>) (RMSE = 9% to 12%). However, the new model well fitted to the same datasets with only 4% error (i.e. RMSE). The Weibull-based model was also good at estimating the germination lag, germination rate and final percent germination in either of weeds studied. Separating the effect of temperature on germination rate and germination extent is suggested to be amongst the most significant ecological properties of the model. For example, the optimum temperature for the mid germination rate (21.8 ^oC in <em>H. spontaneum</em>  and 23.5 ^oC in <em>P. minor</em>) was found to be higher than and beyond the optimum range of germination extent (7.5 to 20 ^oC in <em>H. spontaneum</em>  and 7.5 to 16 ^oC in <em>P. minor</em>). This can give the two species a high degree of germination plasticity in response to the environmental temperatures.   https://ijws.areeo.ac.ir/article_5755_900464fb63b8771fc64c41c4a03dc66e.pdf