Loss of Viability in Lettuce Seeds and the Accumulation of Chromosome Damage under Different Storage Conditions

Abstract

Loss of seed viability in lettuce (Lactuca sativa L.) during storage is associated with an increase in the frequency of cells in the surviving seeds showing chromosome damage during first mitoses. The relation is linear when probit of the frequency of aberrant cells is plotted as a function of probit percentage normal germination. The slope of the relation, however, varies according to moisture content so that the proportion of aberrant cells for any given loss of germination increases with decrease in moisture content over the range 13.0–5.5 per cent. At 3.3 per cent moisture content, however, the proportion of aberrations was no greater than at 5.5 per cent moisture content; and at 18.1 per cent moisture content the proportion was no less than at 13.0 per cent moisture content. Despite these differences, the increase in chromosomal aberrations per unit time for a given temperature was always less the lower the moisture content. Diplontic selection markedly reduced the frequency of chromosomal aberrations and eliminated the differences in these frequencies between the different storage treatments. But even after five weeks' growth, root tips from aged seed still contained about twice as many aberrant cells as compared with similar root tips derived from the original seed stock. Studies on the frequency of recessive mutations indicated that excessive amounts of heritable mutations were not present in the progenies of aged seed, even when stored at moisture contents as low as 5.5 per cent. All this and other evidence reinforces the view that orthodox seeds for genetic conservation should be stored at not more than about 5 per cent moisture content, and that even lower moisture contents are worth considering. The results also emphasise the need for maintaining a high regeneration standard, i.e. the percentage to which seed viability is allowed to fall during storage before the seed stock is regenerated