SEED DORMANCY IN LETTUCE: INFLUENCE OF TEMPERATURE ON INDUCTION AND EXPRESSION OF SEED DORMANCY AND STUDIES ON THE INHERITANCE
It appeared that certain temperatures, such as e.g. a constant temperature of 20°C, induced a clear distinction for degree of dormancy between lettuce cultivars (cvs Magiola and Portato dormant and cvs Deci-Minor and Valore non-dormant). This distinction was optimal at e.g. 23°C during imbibition.
Diallel crosses were carried out between the above four lettuce cultivars to study the inheritance of dormancy.
F1 seeds from crosses between dormant x non dormant cultivars showed a large variation for dormancy compared to the variation of the homozygous parents. The germination time - counted from the beginning of imbibition - was usually intermediate between the dormant and the non-dormant parent. About 40–60% of the F2 seeds from the above crosses germinated within 6–8 days. In F2's from crosses between dormant cultivars (Portato x Magiola) no rapidly germinating seeds were found while in F2's from crosses between non-dormant cultivars (Deci-Minor x Valore) no accumulation of genes for dormancy was found. Comparison of the degree of dormancy of F2 seeds and corresponding F3 progenies from crosses between dormant and non-dormant cultivars showed that h2-narrow was rather large (0.4–0.5) which enables a succesful selection for non-dormant genotypes.
On the basis of the behaviour of the F1, F2 and F3 seeds it is not unlikely that the dormant cultivars (Magiola and Portato) and the non-dormant cultivars (Deci-Minor and Valore) differ for one major gene for dormancy maybe accompagnied by modifier genes.