the effect of temperature and water potential on seed germination of asian spiderflower (cleome viscose l.): as invasive weed in soybean fields in golestan province

introduction: cleome viscose linn. with a common name as “asian spiderflower”, belongs to the capparidacea family. it is an annual, sticky herb found as a common weed all over the tropical regions of the world. it is a very competitive weed of annual crops. this plant is currently introduced as an invasive plant in soybean fields of golestan province. there is no management recommendation to control asian spider flower. thus large quantities of soybean destroyed by this weed every year. germination and emergence are the two most important stages in the life cycle of plants. environmental factors such as temperature, light, ph, planting depth and soil moisture are known to affect seed germination and emergence of weeds. an understanding of the germination biology of asian spider flower would facilitate the development of better management strategies for this weed. therefore, the purposes of this research were to study the effects of temperature and water potential on asian spider flower seed germination. material and methods: to evaluate the effect of temperature and water potential on seed germination and determination of seed germination cardinal temperatures of asian spider flower, an experiment was conducted as factorial experiment in completely randomized design with 4 replications in agricultural research and natural resources center of golestan province during 2013. treatments were included temperatures with seven levels (15, 20, 25, 30, 35, 38 and 400c) and water potentials with six levels (0, -2, -4, -6, -8 and -10 bar). germination was monitored daily until germination discontinued and the number of the germinated seeds was recorded. seeds were observed twice daily and considered germinated when the radical was approximately >2mm long. to quantify the response of germination rate to temperature and to determine the cardinal temperatures for germination original beta, and modified beta, segmented and dent models were used. water potential data showed a sigmoid trend and a three-parameter logistic model was fitted to data (equation 1). y=gmax/ [1+(x/x50)b] where, g is the total germination (%) at concentration x, gmax is the maximum germination (%), x50 is the osmotic potential required for 50% inhibition of the maximum germination and grate indicates the slope of the curve in x50. statistical analysis system (sas) was used for analyzing the data. results and discussion: results showed temperature, water potential and interaction between them significantly affected germination percentage and germination rate, the time required to reach 5% (d05), 10% (d10), 50% (d50), 90%(d90) and 95% (d95) seed germination of asian spiderflower. the results showed that by increasing the temperature to 30 °c, seed percentage and germination rate increased and then decreased. water potential reductions declined seed germination percentage and germination rate. comparing different models to determine seed germination cardinal temperatures, indicated that the segmented model described germination rate changes to temperature better that the others. based on the output of this model, germination base, optimum and ceiling temperatures of the plant were 15.46, 33.21 and 39.64 0c, respectively. the result revealed that increasing the peg concentration, increased the base temperature and decreased optimum and ceiling temperatures. the logistic model fitted with germination percentage of seeds in different water potentials to different temperatures. parameters of the model showed the maximum seed germination percentage occurred in the 25 to 35 0c. highest and lowest x50 parameter (potential required for 50% inhibition of the maximum germination) observed at 30 and 38 0c, respectively. the results showed that the germination ability of asian spiderflower occurred at less potentials water in the optimum temperature range. conclusion: the results showed that high temperatures were required for seed germination of asian spider flower. although water potential has reduced the germination of the weed, we can say this is somewhat drought tolerant plants. based on the segmented model, cardinal temperature for germination, including base, optimum and ceiling temperatures of the plant were 15.46, 33.21 and 39.64 0c, respectively. check the seed germination, percentage changes in water potentials at different temperatures showed that the desired temperature the plant's ability to withstand in adverse environmental condition increases. results of this experiment can be concluded that environmental factors affected the germination of asian spider flower, and this information could help to predict the spread of asian spider flower in new areas.