Cardinal temperatures, response to temperature and range of thermal tolerance for seed germination in wheat (Triticum aestivum L.) cultivars

Understanding the seed germination response of cultivated genotypes to temperatureis important, agronomically. The genotypes that germinate in lower temperaturescould be useful for situations (such as late winter plantings) where temperatures are lowin germination stage. Therefore, this experiment was conducted to study the cardinaltemperatures, response to sub- or supra-optimal temperatures and thermal tolerance ofseed germination in 12 wheat cultivars from the north of Iran. The effects of sevenconstant temperatures between 5 and 34 °C on the seed germination characteristicswere also evaluated. The base (Tb), optimum (To) and maximum or ceiling (Tc)temperatures for germination changed from 2.04 to 2.9°C, 31.81 to 32.42°C and 38.08to 42.08°C, respectively. The analysis of variance revealed no significant differencesbetween cultivars for cardinal temperatures. The effect of cultivar on thermal tolerancewas not also significant, but differences between cultivars for thermal tolerance insupra-optimal temperatures were more than sub-optimal temperatures. Generally, allcultivars were more responsive to supra-optimal temperatures than sub-optimaltemperatures. In the other hand, the slope of regression line of germination rate (GR)versus supra-optimal temperatures was more than that of sub-optimal temperatures. Thedifference between cultivars was significant in response to sub-optimal temperatures,only. The effect of cultivar, temperature and their interactions on germinationcharacteristics including maximum germination (Gmax), time to 10% germination (D10),germination uniformity (GU) and germination rate were significant (p= 0.01),statistically. The evaluated cultivars showed the greatest Gmax in 13 or 20, but the greatestGR in 32°C. Also, D10 and GU decreased as temperature increased to 25 or 32 and 32 or34°C, respectively. The results showed that the difference between 5°C and highertemperatures for Gmax was very less than GR, D10 and GU. This means high Gmax can beobtained in temperatures near to Tb under without soilborn pests conditions.