Relationship Between Azalea Bud Morphology and Effectiveness of Methyl Decanoate, a Chemical Pinching Agent1

Abstract

Abstract Tests in which tips of outer enclosing leaves of vegetative azalea buds were dipped in 4.2% methyl decanoate emulsion indicated that the pinching agent does not translocate in sufficient quantity to kill the meristem. Direct contact must be achieved. A morphological comparison of the vegetative buds of an azalea cultivar responding poorly, ‘White Gish’, and one responding readily, ‘Coral Bells’, to pinching agents indicated that the former has (1) an abnormally long enclosing sheath of leaves and (2) a greater number of trichomes per unit area of leaf surface within the sheath. Both factors can contribute to a reduction in the movement of pinching agent to the meristematic tissue. A comparative study of vegetative and reproductive buds of the azalea cultivar, ‘Red Wing’, gives an account of the reduced effectiveness of pinching agents in reproductive buds. In the young reproductive bud a greater number of leaf primordia layers and in the older reproductive bud the presence of a thick cuticle on the outer scales as well as the presence of numerous closely overlapping scales reduces penetration of the pinching agent emulsion.