Quantification of green bean germination response to simultaneous salt and temperature stress: a modeling approach

Seed germination (SG) is crucial for the survival of plant species; however, it is often subjected to unpredictable environmental conditions such as temperature ( T ) and salinity. Therefore, the objectives of this work were to concurrently investigate salinity and T effects on SG behavior of green bean using a halothermal time (HaloTT) model, to compute the cardinal T s, and to explore the effect of salinity on seeds’ salt ion assimilation (i.e., Na + and Cl − ). Our findings revealed that the effect of salt stress on SG was quantified well by the HaloTT model ( R 2 > 0.82). The estimated cardinal T s at 0 mM were 8.15, 30.0, and 39 °C for the base ( T b ), optimum ( T o ), and ceiling ( T c ) temperatures, respectively. The median threshold NaCl concentration (NaCl b (50)) was 305 mM at T o , then declined linearly at T s ≥ T o , reaching 0 mM at T c . Decreasing germination capability at T s above T o was due to the shifts in NaCl b (50), which appears as a thermoinhibition phenomenon. Na + and Cl − assimilation enhanced significantly with T and seed ψ decreased compared to control. In conclusion, green bean SG was initially controlled by salt osmotic effect (≤ 150 mM), when exceeding this concentration, its effect became both osmotic and toxic.