THE INFLUENCE OF SEEDLING SIZE AND CARBOHYDRATE STATUS AND OF PHOTON FLUX-DENSITY DURING VERNALIZATION ON INFLORESCENCE INITIATION IN ONION (ALLIUM-CEPA L)

Experiments were done in controlled connditions to investigate the relationship of plant weight, leaf number and raising conditions to inflorescence initiation in onion seedlings. Above a shoot dry weight of 0.06 g the spring-sown cv. Rijnsburger could initiate inflorescences, whereas the autumn-sown cv. Senshyu semi-globe Yellow needed to be heavier than 0.45 g. Plants raised at a photon flux density of 200 .mu.mol m-2s-1 and a temperature of 25.degree. C required longer to initiate inflorescences than plants raised at 600 .mu.mol m-2s-1 and 17.degree. C which had higher reserve carbohydrate content. The minimum leaf number for inflorescence initiation was larger for plants with low reserve carbohydrate content. Photon flux densities of 50, 100, 200 and 400 .mu.mol m-2s-1 during vernalization at 9.degree. C caused no differences in inflorescence initiation in plants previously raised at 17.degree. C and 600 .mu.mol m-2s-1 but the lowest photon flux density during vernalization reduced initiation in plants previously raised at 25.degree. C and 200 .mu.mol m-2s-1.