Seed Physiology and Seasonal Emergence of Wild Lettuce Lactuca Serriola

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Abstract
Germination of wild lettuce seeds collected in England [UK], both fresh and after dry storage, was strongly influenced by light and temperature. No germination occurred at 15.degree. C in th dark and far-red radiation reversed the effect of 7 h of white light. Natural temperature fluctuations enabled seeds to germinate in the dark but not beneath leaf canopies. Seeds recovered after burial for 8 wk or longer in the soil germinated in the dark at 15.degree. C and were not inhibited by far-red radiation. Buried seeds had a half-life of approximately 1.5 yr. Germination in field plots took place predominantly in autumn and to a lesser extent in spring. Spring emergence was entirely from seeds which had been sown earlier in the winter and which, presumably, had undergone the same changes in physiology as were observed in those recovered after burial. Loss of the light requirement for germination during burial indicates a reduction in the depth of dormancy as the seeds age which may lead to germination and, although most of these seedlings are likely to die as a result of emergence in unsuitable microsites, some may become established. Even a low rate of survival would ensure that this characteristics is selected since all the seeds are otherwise destined to die.

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