CHARACTERIZATION OF THE GERMINATION RESPONSES TO TEMPERATURE OF LETTUCE (LACTUCA-SATIVA L) ACHENES

Germination tests were done on 23 cultivars of lettuce (Lactuca sativa L.) comprising a variety of different morphological forms selected for cultivation at various seasons.Significant differences at the upper limit of temperature tolerance were found between different cultivars: maximum temperatures for 50 per cent germination ranged from 23 to 32 °C, and susceptibility to the induction of secondary dormancy by high temperatures varied widely from one cultivar to another. No correlations were established between germination responses and heading type, achene colour or growing season. The germination responses of all cultivars at temperatures from just above 0 to 20 °C were closely similar and results from a large number of experiments were used to produce a standard germination reference curve foti culvars of L. sativa. Departfures rom this curve were found to arise predominantly from variations in seed quality or test conditions rather than from the genotype of the cultivar.Detailed comparisons of germination at all possible combinations of alternate and constant day/night temperatures are presented for two cultivars. One with relatively high tolerance to high-temperatureinduced inhibition, the other with low tolerance.The results are discussed in relation to the original distribution of the species as a wild plant and its history of cultivation by man. © 1979, Annals of Botany Company.