Germination models can help predict seed germination in response to different abiotic stress factors. We used the hydrothermal time model (HTT) to study seed germination in two chickpea verities (Parbat and Bittle-98) under different water potentials (Ψ) and temperatures (T). The results indicated that the significant maximum germination percentage (G%) was recorded at 24°C and -0.3MPa, while the lowest was recorded at 6°C and -0.2 MPa. Moreover, both verities exhibited a linear increase in germination rate at different temperatures. For both varieties, the average cardinal temperatures (Ts) were 6°Cfor the base T (T_b), 18°Cfor the optimal T (T_o), and 36ºCfortheceiling T (T_c) over the confidence intervals of HTT coefficients and maximum R²: 0.972. In addition, the highest θT1 for Parbat was recorded at 24°C and -0.3MPa ѱ which decreased with decreasing ѱ (-1.2MPa).  The maximum θT2 value for Bittel-98 was observed at -0.3 MPa) and 24°C in comparison with the control. The highest ѱ_b(50) (base water potential at 50) for Parbat was monitored at -0.31MPa and T_c 36°C. In contrast, for Bittle-98, the highest ѱ_b(50) value was observed at the middle temperature with an irregular fluctuation pattern. The value of θH (hydro time constant) surged with the rise in T to T_o,and the continuous decline was recorded when T>T_o. By analyzing the seed germination data, the hydrothermal time model (HTT) can provide insight into the synergistic impacts of water deficit and altered temperature on germination of seeds in the face of future climatic changes.

Index Terms- Germination, Osmotic stress, Cardinal temperatures, Hydrothermal time constant, Water potential