Post-irradiation ageing effect on chromosomal structural changes and yield in wheat

Abstract

From his early outstanding work on the genetic analysisof mutations induced by X-rays, Stadler (1932, 1954) stated that all the so-called point mutations were actually minutechromosomal aberrations. Sparrow et al. (1961) also have reacheda similar conclusion from their analysis of X-or gamma-ray induced plants of various species. Variation in the sensitivity of plants to radiation has been extensively investigated bySparrow and his colleagues (Sparrow et al., 1961 ; Sparrow ~d Woodwell, 1962; Van't Hof and Sparrow, 1963; Sparrow il ~.,1963; Sparrow, 1965; Sparrow and Sparrow, 1965; Sparrow tl al., 1965) and broad relationships have been established between the extent of injury and mean chromosome volume at interphase. While this information provides an important general guide to the expected sensitivity of crops,considerably fuller information is necessary to predict the outcome of exposure (Sparrow et al., 1965). It has long been known that the ageing of seeds increases the frequency of spontaneous chromosomal aberrations and mutations. Navashin (1933) found spontaneous chromosomal aberrations in only 0.1 percent seedlings of Crepis tectorum grown from fresh seed, but found that 80 percent of the seedlings from 5-6 year old seed had chromosomal aberrations. At about the same time Peto (1933) found similar ageing effects in maize. He found no chromosome aberrations in seedlings from 6 month old seeds, but in seedling from 6 year old seeds he found that 25 percent of them possessed chromosome aberrations. Peto (1933) also found thatfresh barley seeds, subjected to high temperatures with high humidity, produced seedlings with a high frequency of chromosomal aberrations, apparently due to the artificial ageing effect of high temperature and humidity.