Holt B.R. and Bottino P.J. Structure and yield of a chronically irradiated winter rye—weed community . Radiation Botany 12 , 355-359, 1972.-The response of a rye crop ( Secale cereale ) and its weed associates ( Capsella bursa-pastoris, Conyza canadensis and Lepidium virginicum ) to a gradient of chronic gamma radiation was examined in the Brookhaven gamma field. Plants were counted and shoots harvested in three 0·25 m 2 quadrats at each of fifteen distances from a 4100 Ci 60 Co source. Exposure rates varied from 610 to 3·4 R/day. Rye dominated the biomass and productivity of the community at exposure rates below 50 R/day; weeds dominated between 50 and 610 R/day. The productivity of the community declined markedly as rye was eliminated, but stabilized between 50 and 500 R/day as the major weeds sequentially assumed dominance. Responses of individual species were correlated with their inherent radiosensitivities as predicted from variations in interphase chromosome volume. Within the rye crop, the radiosensitivity of agronomic yield components increased with proximity to seed maturation. Rye seed production was twice as radiosensitive as shoot production.