Effects of Temperature on the Germination and Emergence of Lettuce (Lactuca Sativa, L.) Varieties

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Abstract
Summary The response of seed germination to temperature, over the range 5-33°C, was studied for 22 varieties of the Crisp, Cos and Butterhead types of lettuce. The overall patterns of response were similar in all varieties, irrespective of the storage conditions or origin of the seed lot. The optimum temperature for germination in all varieties was between 15°C and 22°C, but there was a marked upper temperature limit for germination ranging from 25.7+0.9°C in cv Hilde to 32.8+0.9°C in cv Avoncrisp. In the main, the Crisp types germinated well at 30°C, which inhibited germination in the Butterhead types. In a field experiment where eighteen of these varieties were sown during a period of hot sunny weather, two distinct patterns of emergence were observed, apparently related to the prevailing soil temperatures and the upper temperature limits for germination of each variety. In varieties with a high upper temperature limit for germination, seedling emergence was rapid even during periods of high soil temperatures, but in those with low upper temperature limits emergence was inhibited, and only began again when soil temperatures fell. A close relation was found between variability in plant size within a crop and the upper temperature limit for germination, high variability being associated with a low upper temperature limit and vice versa.

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