Observation on the Development of Forced Freesia Flower Buds Exposed to High Temperature Just after Chilling and Morphological Classification of Heat Injury at Flowering

Abstract

Corms of the freesia 'Blue Heaven' were chilled wet at 10°C for 5 or 6 weeks and the resulting sprouting young plants were immediately exposed to 24°C for 1, 2, or 3 weeks and then to 10°C until they were planted in a plastic house maintained at 5°C or above on 13 Nov. Flower buds, exposed to the high temperature, were prepared and photographed on a scanning electron microscope (SEM). Based on their morphology, the inflorescence types at flowering were classified into 6 categories. When flower buds were exposed to high temperature during the differentiation of floral primordia, the inflorescence which formed, varied depending on the developmental stages of flower buds at the start of the high temperature treatment and its duration. These inflorescences were classified as "normal inflorescence", "gladiolus bloom" or "abnormal inflorescence" according to the degree of heat injury. The angle between the horizontal and the crossing lines from the base of the first to that of the last floret in an inflorescence is a practical indicator to measure the degree of "gladiolus bloom". Visually normal inflorescence, "pseudo-normal inflorescence", appeared in plants which received the most severe high temperature treatment. These plants initiated leaves and flower buds after abortion of the pre-differentiated flower buds. "Normal" and "pseudo-normal" inflorescences are easily distinguished by the difference in the number of leaves or days from chilling to flowering. Heat injury was less severe if the plants were exposed to high temperatures at a more advanced stage of flower bud development.