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 aestivum L.) vigor are conflicting. The interactive effects of seed size and water stress on germination and early growth of wheat are perhaps important in this regard. Experiments were conducted to measure the effects of seed size and water potential on germination and seedling growth of the soft red winter wheat genotypes 'Auburn' and 'Howell'. In a growth chamber germination test using solutions of mannitol, germination 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 treatments, respectively. In greenhouse soil, shoot dry weight (SDW), root dry weight (RDW), and number of tillers (NT) of 4-wk-old seedlings from large seeds (35 mg seed(-1)) were larger than those of seedlings from medium (26 mg seed(-1)) and small (17 mg seed(-1)) seeds. Soil water potentials of -100 and -300 kPa decreased all three parameters compared 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 Auburn. 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, while 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 ability of larger seeds to produce larger seedlings than smaller seeds thus appears to be more pronounced under drought than under well watered conditions. While it is not known whether larger seedlings (with larger roots) would enhance water supply to the plant by exploring more soil, or would decrease the supply through more transpiration, faster early growth from larger seeds may be advantageous in establishing plants under dry soil conditions.