Evaluation of germination of wheat seeds with different levels of seed vigor by using the hydrotime model

Introduction Hydrotime model and its coefficients are used to investigate the relationship between water potential and germination rate and percentage. The coefficients of this model puts seed quality indexes such as speed and uniformity of germination and tolerance to environmental stresses at the disposal of researchers. The reducing of water potential significantly decreased seed germination percentage, the chance of plant establishment, uniform emergence, germination rate and seed yield. On the other hand, has been reported that priming increases seed germination in stressful conditions such as salinity, drought and temperature stresses. The coefficients of hydrotime model can be also used for assessment of reaction of wheat deteriorated seeds to drought stress, and indicated that priming improved which germination components of wheat deteriorated seeds. According to these, the aim of this study was to evaluate the germination of deteriorated seeds of wheat under drought stress by Hydrotime model and its coefficients evaluation and comparison at different levels of deterioration and priming. Materials and methods This study conducted in seed research laboratory of Gorgan university of Agricultural Sciences and Natural Resources in 2012. In this experiment, wheat seeds of cv. Koohdasht with different levels of vigor were used. For creating different levels of seed vigor, natural deteriorated seeds (two years of storage) and artificial deteriorated seeds (0, 48, 96 and 120 hours at 43 ° C) were used in two priming and no priming conditions. Priming performed with the use of gibberellic acid in 50 ppm. Different levels of water potential obtained by using polyethylene glycol 6000 in four levels included 0, -0.6, -1.2, and -1.8 MPa. Finally, the hydrotime model (θH=[ψ - ψb(g)]× tg) was used to study the reaction of deteriorated seeds of wheat to drought stress and the effects of priming on improving seed germination. Results and discussion The results showed that hydrotime coefficient (θH) increased by increasing in seed deterioration (either artificial or natural) in terms of both primed and control seeds, In other words, the germination rate was decreased. But, the reduction in germination rate in primed seeds was lower than non- primed seeds. So that, the hydrotime coefficient increased at a rate of 14.8 MPa hours by seed deterioration per day in the primed seeds, But in the control seeds this index increased at a rate of 29.6 MPa hours by seed deterioration per day. In fact, priming compared to control treatment reduced the hydrotime coefficient and increased germination rate of deteriorated seeds especially in severe deterioration. Increase percentage of this coefficient in the natural deteriorated seeds was lower than artificial deteriorated seeds, and this suggests that intensity of artificial deterioration is more than natural deterioration. Thus, the damage that caused by artificial deterioration is more than natural storage. In addition, the model output showed that increase in deterioration significantly reduced the uniformity of seed germination (increase ψσb), But priming had not significant influence on seed germination uniformity. Stored seeds has less germination uniformity compared to non-deteriorated seeds (more ψσb). In priming treatments, was not observed any change on this coefficient by increased duration of deterioration to 3.12 days. But with increasing duration of deterioration more than 3.12 days, its value increased, which suggested that priming did not have a positive impact on improving drought resistance. But resistance to drought reduced significantly in severe deterioration conditions. By increasing the duration of deterioration after 3.12 days, increased 4.0 MPa per day. In control treatment, variation of Ψb(50) to deterioration period was different compared to priming. By increasing deterioration to 1.99 days in control, this coefficient was more negative (increased drought resistance). With increasing duration of deterioration, the value of this coefficient increased after this period. Also, priming has not significant effect on Ψb(50) in natural storage conditions. For natural deterioration during two years, the value of Ψb(50) has not significant difference with not deteriorated seeds (for both priming and control). Conclusions Generally these results showed that the deterioration cause decrease of rate, uniformity and drought resistance, and priming only increases the germination rate and no effect on the other components.