Modeling seed germination response of maize with different shapes and sizes using halotime and halothermal time concept

To quantify both the possible impacts of temperature as well as salinity stress on the germination responses of three seed lots of maize (large flat (LF), large round (LR) and small (SM)) and also, to calculate the cardinal temperatures for these seed lots, a laboratory experiment was launched through using halotime and halothermal time models. The experiment was conducted under eight constant temperatures (5, 10, 15, 20, 25, 30, 35 and 40 °C) and at the following four levels of salinity (0, 50, 100 and 200 mM, as provided by NaCl). The salinity tolerance threshold was 230, 241 and 415 mM for LF, LR and SM seed lots. Small seed lot showed the highest germination tolerance to salinity stress when comparison is made to others, thus providing the indication that under soil salinity conditions, germination and optimal seed placement in the field could be affected by various indicators including seed vigor as well as seed size. The salinity threshold amount was decreased linearly by the rise of temperature in all seed lots; so thermoinhibition could be introduced as a compatible approach in stressful situations. For LF, LR and SM seed lots, the cardinal temperatures at 0 mM were estimated to be 10, 9.7 and 8.5 °C for base, 33, 34 and 30 °C for optimum, and 44.6, 44.8 and 46.6 °C for the ceiling temperature, respectively. As a result, the applied models in this survey could accurately predict the germination responses of maize seeds with different shapes and sizes at different temperatures as well as salinity levels.