Morphological Characterization of Early Floral Development in Apple, Pear, and Cherry in the Midwestern United States

A comprehensive evaluation of floral morphogenesis was undertaken in order to characterize the early floral development of apple, pear and cherry flower buds in Ohio. Changes in flower bud morphology were studied during a whole season using apple, pear and cherry cultivars of ‘Fuji’, ‘Bartlett’ and ‘Regina’, respectively, located in a commercial orchard in Berlin Heights, OH. Collection of samples was performed from 40 days after full bloom (DAFB) in all species with a sampling interval of 15 days during spring and summer and 30 days thereafter. Buds were dissected under a stereomicroscope, classified into different stages, prepared and imaged by a scanning electron microscope. In apples, significant broadening of the meristems occurred by 40 DAFB. Four to six lateral floral meristems per flower were consistently seen from 55 to 110 DAFB. Terminal floral meristem initiation took place around 110 DAFB. Up to 160 DAFB, terminal and lateral flowers had developed in most samples with the final sepal number (5) completed. Stamens slowly started to differentiate first in the terminal flower 155 DAFB, and by 230 DAFB most flower meristems had initiated all flower organs. Pears followed the same sequence of flower organ differentiation but with shorter periods of times between stages. A pronounced domed inflorescence meristem was observed 60 DAFB. Lateral flower meristems were rapidly initiated in the bract axils in 10 days after doming. Apex transformed into a terminal flower meristem from 85 to 100 DAFB. By 135 DAFB, the inflorescence is formed and flower organs in the flower meristems started to differentiate. No dominance phenomenon was found between flowers in cherry buds; all flowers developed simultaneously in each stage. At the first collection a prominent broadening of the apex was observed in 95% of the samples, marking the change from vegetative to a reproductive phase. Floral primordia started initially to differentiate from 50 to 75 DAFB and sepal were visible 30 days after this period. Following this stage, the development of petals, stamens, and carpel was evident in this order from 135 DAFB. Flowers enlarged and organs continued to form after 180 DAFB.