Studies on the use of mutagenic agents in plant breeding. II. The effects of dose and seed moisture content on mutation production in Lupinus angustifolius by X-Rays

Abstract

Seeds of Lupinus angustifolius were given X-ray doses of 2.5, 5, 10, and 20 kr at each of 12 moisture contents ranging from 6.1 to 18.1 % (wet weight basis). Various measures of injury were recorded in the X₁ generation, and the types and rates of mutations in the X₂.

At moisture contents below 16%, total mutation rates were closely correlated with X₁ injury. Injury and mutation rate decreased with increasing moisture up to 11–12% moisture, and thereafter remained at a constant minimum up to 16%. Between 16 and 18% moisture there was again an increase in X₁ injury, but not in mutation rate. Between 6 and 12 % moisture, a linear relationship was found between moisture content and the logarithm of the dose required to cause a given level of injury or mutation. A possible mechanism for such a pattern of protection is discussed.

Lethal mutations increased as a proportion of all mutations as dose and mutation rate increased. There were also proportionately more lethals at high moisture contents than in lower moisture treatments giving the same mutation rates. It is concluded that lethal and seedling chlorophyll-deficient mutations could be misleading when used as indicators of total and viable mutation rates, and that, contrary to the conclusions of some previous authors, no advantage is likely to be gained in practical breeding work from irradiating at high seed moisture contents.