The Impact of Short-term Thermal Stress on the Consequent Germination of Dill Seeds

Abstract

The authors obtained new data on the germination of dill seeds, which were gathered from the first-order and second-order branches, after short-term thermal stress (40 °C). The seeds were germinated in a thermostat. The swollen seeds (4 replications with 100 seeds each) were incubated at 40 °C for 1 to 5 days. The seeds in the control group were not incubated. After the incubation, the seeds were transferred to the standard (t = 20 °C) conditions and germinated on filter paper in Petri dishes without light for 21 days. In this study, the authors employed the dynamic method of seed germination analysis. To plot the seed germination curve, the authors used a log-logistic regression with three parameters: b, d, and e. The statistical analysis was conducted in R 3.4.3. The authors determined the duration of heat stress that inhibits the germination speed and germination rate of seeds. Seeds gathered from the first-order branches (“first-order seeds” from now onward) after 1-day to 3-day incubation germinated similarly to the control group. Increasing the incubation period to 4–5 days sharply reduced the germination speed. Seeds gathered from the second-order branches (“second-order seeds” from now onward) were less resistant to high-temperature stress. Three-day incubation completely precluded germination. The germination time of 50% (T50) of the first-order seeds slowed by 0.92±0.11–6.4±0.49 days because of the gradual increase in incubation time. The second-order seeds that incubated for 1–2 days germinated significantly slower than the control group seeds. After this point, further incubation precluded germination. Upon reaching the incubation threshold, the germination rate curves steepened and then continued falling up to the full germination stop. The maximum incubation time (at 40 °C), after which germination was possible in standard temperature conditions, was 3.69±0.06 days for the first-order seeds, and 2.00±0.19 days for the second-order roots. The differences in data were statistically significant at p-value < 0.001