Acute gamma irradiation of the soybean plant: effects of exposure, exposure rate and developmental stage on growth and yield

Abstract

Soybean plants (Glycine max (L.) Merrill “Kent”) were exposed to 60Co gamma radiation and grown to maturity in containers under outdoor conditions. The effects of developmental stage of the plant when irradiated, exposure, and exposure rate on growth (stem length) and yield were investigated. Yield showed a greater degree of sensitivity to gamma irradiation than did stem length. Stem length was reduced to approximately 50 per cent of the non-irradiated population when plants in the early log phase of growth (2- to 4-trifoliolate leaf stage) were exposed to 2·5 kR at 50 R/min. Stem length reduction was 10 per cent when plants were exposed during the lag phase (unifoliolate to 1-trifoliolate leaf stage), and ranged from 40 per cent to less than 10 per cent when the plants were exposed during mid-log and decreasing phases of growth (5- to 13-trifoliolate leaf stage), respectively. Yield was zero when plants in the log phase of stem growth were exposed to 2·5 kR at 50 R/min. Flower bud development and gametogenesis occurred during this period. Exposure of the soybean plant during the lag phase to 2·5 kR caused a 60 per cent reduction in yield, whereas the same exposure during the decreasing phase (late embryogenesis) caused a 20 per cent reduction in yield. Plants exposed during the lag and log phases of growth showed a 50 per cent reduction in yield at 1·3–2·1 kR, respectively, and their yield was reduced by 80 per cent at an exposure of 4·0 kR at 50 R/min. Exposure rate did not affect stem length at 2·5 kR, whereas at 5·0 kR the damage became independent of rate at 25 R/min. Exposure rate affected yield at both 2·5 and 5·0 kR when plants were irradiated in the log phase of stem growth and damage became independent of rate at 12·5 R/min.