Flower and corm development in gladiolus as affected by photoperiod

Gladiolus plants cultivar ‘Spick and Span’ were grown in winter under natural short day (SD) or under long day (LD), with 4 hours low intensity light at midnight. Growth of the various organs was followed by periodic sampling. SD promoted flower development and advanced anthesis but reduced the final size of the flower. LD increased weight and size of leaves and flowers.Initial growth of the corm was similar under both photoperiods, but while corm growth continued throughout the growing-period under SD, it was checked under LD when flowers were developed at an enhanced rate and until anthesis. At this stage, the allocation of assimilates was directed towards the flower sink and away from the corm sink.Final corm weight was also promoted by LD. This is interpreted as an indirect effect due to increased photosynthesis of the larger LD plants. In non-flowering plants raised from cormels, SD specifically promoted corm growth, although no competing flower sink was present.It is concluded that photoperiod affects growth and development of gladiolus in two ways: directly — by affecting the partitioning of assimilates between the flower or the corm; and indirectly — by affecting the total photosynthates available to the plants by influencing foliage size and the total growth period.