Invigoration of Cotton Seedlings by Treatment of Seeds for Pregermination Activities

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Abstract
Incubation of cotton seeds (Gossypium hirsutum, cv. Acala S.J. 2) at 20 °C and 95% r.h. for up to 12 d results in an increase in seed water content and in a higher rate of seedling development. When seed vigour is measured by tolerance to high temperature storage (aging conditions) or tolerance to low temperature and salinity during germination, seeds incubated for up to 4 d are more vigorous than the control seeds. Hence, such a presowing treatment of seed could be used for seed invigoration. As the incubation proceeds, although a higher growth rate of seedlings is obtained at optimal conditions, the tolerance to stress conditions declines proportional to the duration of incubation. Results of chemical and biochemical examinations of the incubated seeds are compared with those of seeds during normal imbibition for germination. The early stage of germination (up to 4 h) is accompanied by a decrease in reducing sugars and amino acids. At the later stage, an increase of these components and a decrease in the lipid fraction occur. During the first 4 h, an increase and decrease of phosphoenolpyruvate carboxylase and of malic dehydrogenase occur. According to the chemical and biochemical markers, it is evident that seed treatment at 20 °C and 95% r.h. results in pregermination biochemical activities. The first 4 d seem to be equivalent to the first 3 h of germination under normal conditons. At this period of time, degradation processes are taking place. If incubation is continued the resynthesis stage appears to be retarded by the low moisture available and therefore degradation processes continue, resulting in loss of seed vigour. The resynthesis ability may therefore be a prerequisite for the following steps in seed germination.