Viability of Lettuce Seeds

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Abstract
Lettuce seeds were stored under aerobic conditions at various temperatures from 20 °C to 35 °C, under anaerobic conditions at 35 °C, and at various moisture contents ranging from 17% to 44%, controlled osmotically by polyethyleneglycol. Survival of these seeds was compared with others maintained over a similar range of temperatures and moisture contents but in which the moisture contents were controlled by hermetic storage. Irrespective of the method of controlling moisture content, under anaerobic conditions the trend (shown previously in drier seeds) of decrease in longevity with increase in hydration continued up to about 27% moisture content, but above this value there was no further change in longevity. In contrast, under aerobic conditions longevity increased exponentially up to 44% moisture content, this increase starting at about 15% moisture content at 20 °C and at about 24% at 35 °C. Under all circumstances longevity was less at higher temperatures. On a water substrate, thermodormant seeds showed a rapid increase in rate of oxygen uptake, followed by a rapid decline, and then a slower decline to a steady state. Similar phases were shown in seeds of various moisture contents controlled osmotically down to 17%, although the corresponding rates were lower with decrease in moisture content and temperature, and the phases were extended at lower temperatures. The implications of these results are discussed in relation to the conditions needed to sustain sub-cellular repair and turnover as postulated by Villiers.

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