Effect of High Temperature Treatment on Nonuniform Flower Coloration in Spring-harvest Cropping Type of Eustoma ‘Voyage (Type II) Blue’

Abstract

The flowers of spring-harvest cropping types of Eustoma occasionally exhibit nonuniformly colored petals. In the center petals of such flowers, pale greenish areas remain after flower opening. In this study, the effects of cultivation at high ambient temperatures (27°C) at the presumed flower-bud differentiation stage on the percentage of flowers with nonuniformly colored petals was investigated. The daily mean temperature in a greenhouse in Ibaraki Prefecture was less than 19°C from January 7 to February 18 (period of high-temperature treatment). The percentage of terminal flowers exhibiting nonuniform coloration was lower in plants cultivated at high ambient temperatures for 7 days starting from January 14, 21, and February 4, and for 14 days starting from January 7, 14, 21, 28, and February 4 compared with low-temperature treatment (controls). Compared with the controls, the percentage of lateral flowers with nonuniform coloration was lower in plants subjected to high ambient temperatures for 7 days starting from February 4 and for 14 days starting from January 28 and February 4. Similarly, fewer petals, stamens, and pistils tended to be produced at high ambient temperatures compared with the controls. In addition, numbers of petals, stamens, and pistils of terminal and lateral flowers with nonuniformly colored petals were significantly higher than those of normal flowers. The results showed that the petal number increased when plants were grown at low daily mean temperatures. Under these conditions, the developmental stage of inner petals may differ markedly from that of the outer petals, producing nonuniformly colored flowers. Increasing ambient temperatures during flower initiation and development is thus an effective means to reduce the production of nonuniformly colored flowers.