The effects of seed vigour and moisture stress on the germination and seedling establishment of wheat and sorghum
The experiments reported in this thesis assessed vigour differences between seed lots of wheat and sorghum under suboptimal conditions. A vigour assessment for each lot of both species was quantified by calculating a value for the viability equation constant Ki. Imbibition of seed lots at lower water potentials reduced water uptake, radicle and coleoptile emergence and their subsequent extension. Similarly, seeds aged by controlled deterioration also resulted in reduced radicle and coleoptile emergence and growth compared to that of unaged seeds. The critical water potential for radicle emergence, coleoptile emergence and their subsequent extension was lower for sorghum than that required for wheat. In both species coleoptile emergence and its subsequent extension was more sensitive than radicle emergence and extension. Tolerance of desiccation of both species decreased as germination progressed. However, imbibition of seeds for 24 h and drying back to their original moisture content promoted seed invigoration in some cases. Cells from seminal roots of wheat and sorghum were shorter when imbibed in lower water potentials than when they were imbibed at higher water potentials. The high drought tolerant cv (DJ1) showed lower root solute potential than the low drought tolerant cv (IS9). The results discussed in this thesis indicate that the information derived from controlled deterioration might be used as an indicator of planting value under sub-optimal conditions.