Redroot Pigweed (Amaranthus retroflexus) Seed Germination Responses to Afterripening, Temperature, Ethylene, and Some Other Environmental Factors

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Abstract
Germination responses of redroot pigweed (Amaranthus retroflexus L.) seeds to temperature, water potential, atmospheric ethylene and carbon dioxide concentrations, light, and nitrate ion were examined individually. Seeds kept in dry storage at −20 C and tested within 2 yr of harvest germinated at 35 C (12 to 25%) or 39.5 C (40 to 65%), but only 0 to 2% at 30 C and below. Germination at 35 C was prevented by water potentials below −4 bars. When seeds were kept in dry storage at 24 to 28 C, afterripening became evident within 2 months. After storage at this temperature for 4 yr, seeds showed 38% germination at 14 C, 40% at 35 C and −8 bars water potential, and over 90% under more favorable conditions. Ethylene (1 to 100 ppmv) or continuous light enhanced germination at 30 C regardless of degrees of afterripening, although the ethylene effect was most dramatic in nonafterripened seeds. Ethylene at 100 ppmv caused 40% germination in these seeds, compared to 1% for controls. Neither carbon dioxide (0.001 to 4.5% v/v) nor dissolved potassium nitrate (0.02 to 0.2% w/v) influenced germination. These results are discussed in relation to environmental factors influencing field emergence of redroot pigweed.