Growth response of sorghum plants to chilling temperature and duration of exposure

Sorghum is a species sensitive to chilling temperatures. In the cultivation areas at higher latitudes chilling sensitivity may significantly influence plants growth in early spring, resulting in significant yield reductions. The effects of chilling stress were investigated in a controlled environment experiment on sorghum plants fertilised with 0 and 44 mg per pot of N. Plants were grown at 27° C until eighth leaf development stage, exposed to 2, 5, and 8° C for time period varying from 1 to 8 days, and then returned to 27° C. Dry weight of plants, leaf area and N and P concentration and content were determined before and after each period of cold treatment and after a 10-day recovery period. Plant relative growth rate (RGR), leaf relative growth rate (RLGR) and N and P uptake rates were calculated during the chilling and the recovery period. Chilling treatments greatly inhibited sorghum growth and N uptake during chilling exposure. The nature and severity of chilling damage was a function of the severity and duration of the exposure: plants suffered short chilling injury at all temperatures, when the duration of chilling was prolonged plants were able to react to chilling, but the ability of the plant to adapt decreased with the decrease of temperature. Plant shoot growth was found to be more sensitive to chilling than leaf area growth and non-fertilised plants were more tolerant to chilling than N-fertilised plants. Also the ability of the plant to recover was a function of the severity and duration of the exposure and of N availability. The recovery of growth rate decreased as temperature was lower and as exposure was longer. Non-fertilised plants were able to recover higher growth rates following chilling stress than N-fertilised plants, while for N uptake the reverse was true, with N-fertilised plants having higher N uptake rates than non-fertilised ones.