FACTORS CONTROLLING THE RESPONSE OF FIELD CROPS TO VERY LOW DOSES OF GAMMA IRRADIATION OF THE SEED

Abstract

Stimulation of growth by very low doses of ionizing radiation, or hormesis, is a widely documented phenomenon. The biochemical mechanisms are unclear and the phenomenon is sporadic, controlled by factors as yet only poorly understood. Our study addressed factors reported to control the growth response of plants to seed irradiation. A growth chamber experiment compared the effects of four radiation sources on three crop species. Early emergence of flax (Linum usitatissimum) and early growth of wheat (Triticum aestivum) and barley (Hordeum vulgare) were increased by irradiation. These effects did not vary as a function of the photon-energy or dose-rate of the sources. Three field experiments were conducted where various cultivars and seed lots of wheat were irradiated at doses of 0.5–50 Gy using Cobalt-60. Early emergence was significantly accelerated in 7 of 18 seed lots. Grain yields were significantly increased in five cases for Neepawa or Glenlea cultivars, but were significantly decreased in nine other cases. The effects were not consistently related to measured seed lot characteristics, manipulation of the seed moisture content prior to irradiation, or the post-seeding environment as varied by delayed planting. In conclusion, there was some evidence of hormesis in emergence and early growth, but these effects did not persist to yield a benefit at harvest.Key words: Hormesis, stimulation, wheat, barley, flax, irradiation