The effect of various environmental factors on flowering of gladiolus. II. Length of the day

Abstract

In summer, shortening the length of the daylight period (SD) caused a decrease in either the flowering percentage of Gladiolus, or the number of florets produced per spike, or in both parameters according to the degree of sensitivity of the cultivar in question. In all cultivars tested, SD prevented the production of secondary inflorescences. Sensitivity to SD treatment differed at the various stages of development. Flowering percentage was especially affected by SD treatment when applied during the period lasting from emergence of the 1st to the appearance of the 5th foliage leaf. In contrast, SD applied from the 4th leaf stage to anthesis reduced the number of florets per spike. The stage from the appearance of the 4th leaf to spike emergence was most sensitive since both the flowering percentage and the number of florets per spike were reduced. The effect of SD treatment was similar to that of reduction in light intensity ( Shillo and Halevy, 1976) and is apparently due to a reduction in total solar irradiance. In winter, photoperiodic low light intensity extension of natural daylength (LD) delayed flowering and increased the number of florets per spike, the number of secondary inflorescences and sometimes also the flowering percentage. Plant response to LD treatment was similar at all stages of flower development.