EFFECTS OF TEMPERATURE OF MOTHER-PLANT ENVIRONMENT ON YIELD AND GERMINATION OF SEEDS OF LETTUCE (LACTUCA-SATIVA)

Experiments on the production of two separate crops of lettuce seeds, each in three different temperature environments, and subsequent tests on the seed are described. Low production temperatures (20 °C day, 10 °C night) gave a low yield of large seeds, and high temperatures (30 °C, 20 °C) gave a higher yield of much smaller seed; the highest yield came from medium temperatures (25 °C, 15 °C), which gave medium-sized seed. After-ripening, manifested as an increase in percentage germination at high temperatures with increase in seed age, occurred in seed from all three production environments of the first crop, though there were differences in degree, and in that from the two higher production temperatures, but not the lowest, of the second crop. Measurements of the forces required to penetrate the layers surrounding the embryo showed an inverse relationship with temperature of the production environment for pericarps but not for endosperms, and a gradual reduction during storage for pericarps but not endosperms. Measurements of germination potential showed that embryos from seeds produced in cool conditions were less able to cope with high temperatures than those from warner conditions. These results are discussed in relation to the control of germination in lettuce. © 1990 Annals of Botany Company.