Determination of Cardinal Temperature and Evaluation of Germination Characteristics of Syrian Thistle (Notobasis syriaca) in Response to Temperature Range and Salinity and Drought Stresses

Notobasis (Syrian Thistle (has been introduced as a weed - medicinal plant. In Khuzestan province, the presence of Notobasis is abundant in cereal fields, especially field margins. For successful weed control, knowledge of weed biology and ecology (temperature, salinity and drought stresses) plays a key role in population dynamics of weeds and weed management. Therefore, the study aimed to evaluate Syrian Thistle response to temperature, salinity and drought, as well as to determine the cardinal temperature based on segmented, beta-four-parameter and dent-like models.

To investigate the effect of temperature (5, 10, 15, 20, 25, 30, 35 and 40 °C), salinity (zero, 50, 100, 150, 200, 250 and 300 mM) and drought stress (zero, 2) -0.0, -0.4, -0.6, -0.8, -1, -1.2 and -1.4 MPa). Three separate experiments were conducted in 2019 at agricultural science and natural resources university of Khuzestan at the laboratory of weed science with 6 replications. In each Petri dish, 25 seeds were placed and 7 ml of solution was added. In salinity and drought stresses experiments, sodium chloride solution and polyethylene glycol 6000 were used.

Germination of Notobasis at temperatures of 5-30°C was more than 90%, and germination percent decreased to 24% as the temperature increased to 35°C, Based on three models segmented, beta 4 parameter and Dent-like, the Base temperature was estimated 2.95, 2.01 and 0.67°C respectively. Also, the optimum temperature in two models (segmented and beta parameter) was obtained 22.26 and 23.40°C respectively. Ceiling temperature was predicted 40.57, 39.75 and 40.03°C in three models (segmented, beta 4 parameter and Dent- like). Salinity required to reduce 50% of germination percentage, germination rate, seedling length and seedling fresh weight were 152, 85, 151 and 127 mM. 50% reduction of traits such as germination percent, germination rate, seedling length and seedling fresh weight were -0.81, -0.41, -0.43 and -0.45 MPa of drought stress respectively.

 The results indicated that Notobasis had germination in a wide range of temperatures (5-35°C). In response to environmental stress, Notobasis have been identified as a weed resistant to salinity and drought stresses. Therefore, the presence of this weed in saline fields and arid areas is not unexpected.

1-To determine of cardinal temperature of Notobasis based on different models.2-To evaluate germination ecology of Notobasis to environmental factors (temperature, salinity and drought stress) as the first report.