Effects of Exposure to 30°C for Various Periods on Shape and Rates of Coloration in Eustoma grandiflorum Picotee Cultivar Petals

Abstract

The relationship between exposure to a daytime temperature of 30°C for various periods and the ratios of colored areas in petals of the picotee cultivar of Eustoma grandiflorum was investigated under an artificial climate. To determine the conditions under which petals with various color ratios appeared, plants were cultivated at a nighttime temperature of 15°C and for 0, 2, 4, 6 and 10 hours in the daytime at 30°C in artificial climate chambers from the stage of pistil formation of the first flower bud to harvest. Daytime exposure to 30°C for 2 hours caused 10-90% coloration of the area of each petal. The ratio of the petal length to width under this condition significantly and negatively correlated with the coloration rates of petals in the second and third florets. These findings suggested that petal coloration rates increase at low temperatures concurrently with a change in petal form. Moreover, daytime exposure to 30°C for 4 or 6 hours resulted in a maximal coloration rate of 40% of the whole petal area and almost all petals were colored at a rate between 10 and 30%. The mean petal coloration rate was about 15% when exposed for 10 hours to a daytime temperature of 30°C and ‹ 10% of the area was colored in 24% of petals. These results suggested that the coloration ratio of petals can be controlled by the duration of daytime exposure to a temperature of 30°C.