SEED SIZE AND WATER POTENTIAL EFFECTS ON GERMINATION AND SEEDLING GROWTH OF WINTER-WHEAT

Published reports on the effects of seed size on wheat (Triticum aesti vum L.) vigor are conflicting. The interactive effects of seed size an d water stress on germination and early growth of wheat are perhaps im portant in this regard. Experiments were conducted to measure the effe cts of seed size and water potential on germination and seedling growt h of the soft red winter wheat genotypes 'Auburn' and 'Howell'. In a g rowth chamber germination test using solutions of mannitol, germinatio n percentage (GP) was not affected by seed size, but osmoticum of -300 kPa reduced GP to 69 compared to 88 and 89 for the 0 and -100 kPa tre atments, respectively. In greenhouse soil, shoot dry weight (SDW), roo t dry weight (RDW), and number of tillers (NT) of 4-wk-old seedlings f rom large seeds (35 mg seed(-1)) were larger than those of seedlings f rom medium (26 mg seed(-1)) and small (17 mg seed(-1)) seeds. Soil wat er potentials of -100 and -300 kPa decreased all three parameters comp ared to the control (-10 kPa). The GP in the greenhouse was reduced by low water potential, but was not affected by seed size. The genotype x water potential interaction was significant for SDW and RDW, but not for GP and NT; Howell was more susceptible to water stress than Aubur n. At - 10 kPa, 4-wk-old plants from small seeds had SDW and RDW that were 30 and 39% smaller, respectively, than those from large seeds, wh ile at -300 kPa, SDW and RDW of plants from small seeds were 75 and 78 % smaller, respectively, than those of plants from large seeds. The ab ility of larger seeds to produce larger seedlings than smaller seeds t hus appears to be more pronounced under drought than under well watere d conditions. While it is not known whether larger seedlings (with lar ger roots) would enhance water supply to the plant by exploring more s oil, or would decrease the supply through more transpiration, faster e arly growth from larger seeds may be advantageous in establishing plan ts under dry soil conditions.