Seed germination and seedling growth of three sorghum (Sorghum bicolor L.) genotypes as affected by low temperatures

Sorghum (Sorghum bicolor L.) originated in the semi-arid tropics and generally is sensitive to low-temperature stress. Chilling stresses include low temperature (below 20 °C) and freezing injury (below 0 °C). In this study seed germination and seedling growth of three sorghum genotypes (KFS1, KFS2 and Speedfeed) were examined under four temperature regimes (35/15, 20/10, 13/10 and 11/8) conditions. The results showed that low temperature reduced germination percentage, rate of 50% germination,vigour index, shoot and root length, as well as, shoot and root dry weight; whereas it increased emergence index and root to shoot length ratio (R/S). So that, the seeds of sorghum genotypes (on average) was germinated 10.5 days later at 11/8 than 25/22 temperature regimes. Increased R/S in low temperatures might be an indication of water deficit stress due to cold stress. Since in most traits, there were no significant difference between 25/22 and 15/10, thus the lower temperature regimes below 15/10 could considered as cold stress. The sorghum genotypes responded differently to low temperatures, which it seems that KFS2 and Speedfeed were the most tolerant and sensitive genotypes to low temperature. Further researches about biochemical responses of these sorghum genotypes to low temperature regimes are needed.