1958 Volume 27 Issue 4 Pages 234-240
1. In order to obtain the basic data for breeding and seed production in spinach, experiments were carried out on the low temperature induction of bolting using the following 13 varieties of spinach differing in photoperiodic requirement: Nihon-zairai, Ujô, Jirômaru, Wakakusa, Hôyô (those are early bolters) ; Hollandia, Viroflay, Long Standing, Minsterland, Nobel, King of Denmark, Seiyôôba, Sapporoôba (those are slow bolters).
The seeds were subjected to 2±1°C for two weeks and then sown in clay pots or on beds in greenhouses in spring (March 5), in summer (June 5) and in autumn (October 5).
2. The time of initiation of floral primordia of all the varieties tested was accelerated by the low temperature treatment, as compared with the con-trols in each season, and the floral initiation of the treated plants of those varieties started at about the same time.
3. The promotion of bolting and flowering was also markedly shown in the treated plants, but varietal differences remained unchanged in the time of development of flower stalks, especially under short-day conditions in autumn or winter.
From these results, it was assumed that the after effect of the vernalization treatment might shorten the length of photoperiod required for induction of each variety, but it did not alter the varietal order in their photoperiodic requirements necessary for inducing flowering.
4. The possibilities for getting high yields of seeds of the slow bolting varieties planted in spring by the vernalization treatment seemed to be promising.