Effect of thermo-priming on germination, agronomic characteristics and seed oil of safflower (Crthamus tinctorius) cultivars

Safflower (Carthamus tinctorius) is one of the oilseed crops in arid and semi-arid regions. Germination and heading stages are considered as the most sensitive developmental stages of safflower. Therefore, the aim of the present study was to determine the effect of thermo-priming on germination characteristics of the safflower seed in the laboratory and then, to evaluate the effect of this type of priming on some agronomic traits, yield and percentage of seed oil of safflower genotypes in the field. In the first stage, a factorial experiment was conducted based on a completely randomized design with three replications in laboratory condition. The experimental factors included thermo-priming (40, 60 and 80 ° C) at three times (6, 10 and 20 h) and safflower genotypes (primed and non- primed seeds). Germination percentage of seeds and seed germination rate were measured. Then, based on the results of the first stage, another factorial experiment was conducted based on a randomized complete block design with three replications. Safflower genotypes were primed only at 60 ° C at two times of 6 and 10 h (non- primed seeds were considered as control) and then days to 50% emergence, days to maturity, number of heads per plant, 1000-seed weight, seed yield per plant and seed oil percentage were measured during the experiment and at the end. The results of the first stage revealed that pre-sowing seed treatment by thermo-priming had a significant effect on the percentage and rate of germination. The highest percentage and rate of germination were obtained at temperatures of 40 and 60 ° C in the short period of priming (6 and 10 h). In field, according to the results of the first stage, pre-treatment of seeds at 60 ° C resulted in a reduction of the day to 50% seed emergence in primed genotypes compared to the control genotypes. On the other hand, thermo-priming resulted in increasing the day to maturity, seed yield per plant and percentage of seed oil, but the number of heads per plant was not affected by thermo-priming. In general, the results indicated that pre-treatment of seeds with thermo-priming (medium temperatures) resulted in the rapid emergence and establishment of safflower seedlings. Moreover, the results showed that thermo-priming at 60 ° C not only had no negative effect on safflower seed yield and percentage of oil, but also significantly increased the traits in primed genotypes compared to non-primed ones. It is worth noting that the spring planting of primed seeds of safflower can lead to improved seed yield and oil yield compared to planting of non-primed seeds.