Response of Cumin (Cuminum cyminum L.) Ecotypes to Drought Stress during Germination Stage at Low Temperature

 Cumin is one of the most important medicinal plants in Iran and is widely used in food, health and beauty industries due to its antioxidant and antibacterial properties. Yield of some crops are higher in autumn planting compared to spring. However, low temperature and inappropriate distribution of precipitation are of factors affecting seedling emergence and establishment. So it seems that seeds with higher germination also have better emergence and establishment producing more vigorous seedlings in further growth stages. So, to success in autumn-planting of cumin, it is necessary to have ecotypes with appropriate and even emergence in low temperature and water restricted conditions. Since water is of high paramount importance in germination and lower water potentials lead to lower accessibility of water to seeds, the aim of this experiment was to study seed germination response of different cumin ecotypes to low water potentials.

This study was conducted to determine the germination of six cumin ecotypes under drought stress and low temperature conditions. Treatments comprised of six cumin ecotypes (Torbat-e-Heydarieh, Khaf, Sabzevar, Qaen, Quchan and RZ19) and seven water potentials (0, -1, -2, -3, -4, -5 and -6 bar) induced by  PEG6000 solution according to Michel B. E. and Kaufmann (1973). Distilled water was used for control. Seeds were disinfected by sodium hypochlorite (10%) and fungicide and were rinsed with distilled water. 25 seeds were placed in each petri dish and were incubated in 13°C after PEG solution or distilled water was added. Germinated seeds were recorded daily and germination percentage and rate, plumule and radicle length was determined at the end of the incubation. Ecotype ranking was also performed to determine the most tolerant ecotypes to drought stress. Statistical analysis was done using MSTAT-C and LSD test was used for mean comparison.

This study results indicated that water potentials was significantly affected all studied traits (p<0.05) in a way that germination percentage and rate and plumule and radicle length decreased as water potential decreased to -6 bar. Maximum germination percentages (61%) was obtained in control. Significant differences were also found among cumin ecotypes for all traits. Khaf and Torbat-e-Heydarieh had the highest germination percentage (25% and 23%, respectively). Decreasing water potential from 0 to the -2 bar, caused 69% decrease in germination percentage of Quchan ecotype whereas reduction of 43% and 57% was found in Qaen and Sabzevar ecotypes, respectively. Difference in germination percentage among genotypes may be due to the different water absorption by them. Ecotypes had different germination rate in water potentials (P≤0.01). Although germination rate was negatively affected by decreasing water potential, percentage of reduction was different among ecotypes in a way that Torbat-e-Heydarieh and Khaf showed the lowest (61 and 67%) and Quchan and RZ19 the highest reduction of germination rate (86%) in -4 bar compared to control (0 bar). Plumule and radical length were decreased as drought stress was increased . Decreasing water potential from 0 o -4 bar caused a 76% reduction in radical length. Significant difference was found among ecotypes according to radical length in a way that Khaf and Quchan had the highest and lowest radical length, respectively.

On the basis of ecotypes ranking for evaluated traits, Khaf and Torbat-e-Heydarieh indicated more tolerance to drought stress whereas Quchan was found as a sensitive ecotype.