Floral initiation in wheat

Abstract

The gap in understanding between genetic control and physiological processes of differentiation is far from being bridged; but it is being narrowed by a coordinated approach from both directions. The genetic system controlling the stability of floral differentiation in a series of wheat genotypes with progressively disturbed floral morphogenesis provides an experimental means of investigating the elements of the physiological system controlling floral initiation and development. Selected genotypes were exposed to an environmental treatment of short days with high temperatures, starting at precise intervals during early spikelet and floret differentiation. The effects were ascertained at ear emergence and corroborated by histological examination throughout and after treatment. A sensitive period for each floret was detected between the initiation of the subtending lemma and the initiation of the floret itself. Over the inflorescence as a whole, sterility gradients were recognized which were characteristic of the respective genotypes and clearly under genetic control. These gradients are explained on the basis of an activator substance interacting with, but distinct from the developmental gradient of the spike. It is suggested that the same elements - sensitive stage of floral initiation and activator gradient - play a major role in the floral differentiation of normal genotypes.