Estimating Cardinal Temperatures of Milk Thistle (Silybum marianum) Seed Germination

The objective of this study was to quantify response of germination rate to temperature and calculating cardinal temperatures in Milk thistle (Silybum marianum). An experiment was conducted at Agricultural Laboratory of Department of Agriculture ( Islamic Azad University, Ramhormoz Branch, Ramhormoz, Iran) during 2011. Seeds were incubated on moist filter paper and germinated at constant temperatures ranging from 0 to 45°C (0, 3, 9, 15, 21, 27, 33, 39 and 45°C) in petridishes. A total of four replicates were used in CRD design. Collected data used to plot mean cumulative germination curves against time. To describe the germination rate response to temperature, a segmented model was used. Hence, cardinal temperatures were obtained by fitting a segmented, non-linear regression model to data of germination rate versus temperature. Results showed that the mean of calculated cardinal temperatures were 1.35°C for base, 20.51°C for optimum and 41.81°C for ceiling temperate in Milk thistle. Also, the maximum germination rate at which germination occurs in minimum time, was 2.72 d . Calculated cardinal temperatures can be used in other 1 researches with different objects, such as prediction of subsequent development stages of the crops and selection of appropriate sowing date and etc.