Acquisition of Seed Desiccation Tolerance and Vigor in Wheat (Triticum durum) During Maturation as Influenced by Drying Methods.

Two field experiments were conducted to study the effects of seed maturity and four drying treatments on seed desiccation tolerance and vigor of wheat during maturation. Spikes of wheat grown during the 2005/6 and 2006/7 seasons were hand harvested at five seed development stages: milk-stage, soft-dough stage, hard-dough stage, physiological maturity, and harvest maturity. Seeds were dried by four methods: 1) attached to their spikes; 2) detached and dried under ambient conditions; 3) detached and dried slowly; 4) detached and dried quickly. Standard germination (SG) and germination after three accelerated aging (AA) (100% relative humidity and 41^oC for 72 h, 42^oC for 96 h, or 45^oC for 48 h) were measured. Seeds dried in their spikes had higher SG and vigor (germination after three AA tests) than those detached and dried under ambient, slow, or fast treatments at the milk-stage in both years. The SG for all drying treatments did not differ at the soft-dough stage and beyond. Spike-dried seeds achieved maximum vigor at the SD stage in both seasons, earlier than detached seeds dried under ambient, slow, or fast treatments. Spike-dried seeds had significantly higher vigor at the soft-dough stage than detached seeds dried under fast treatment. At later maturity stages (HD, PM, and B stages), spike-dried seeds had high germination after all AA tests (>84%) in both years, while detached seeds varied in AA-germination between years. All detached seeds in 2006/7 had lower germination after AA tests (42^oC for 96 h and 45^oC for 48 h) than 2005/6, suggesting that those two AA tests discriminated the differences among the drying treatments better than the AA of 41^oC for 72 h. In conclusion, drying the seeds in their spikes preserved seed desiccation at the milk stage and seed vigor at later developmental stages, suggesting that spike-drying of wheat seeds maintained more stable seed quality across developmental stages and years.