The fascicled ear (Fas) mutation --Samuel Postlethwait and Oliver Nelson We wish to call the attention of the maize genetics community to an interesting developmental variant that affects the floral structures of maize. We received this mutant stock over thirty years ago from Paul Weatherwax of Indiana University and have designated the mutation as fascicled ear (Fas). It is a dominant mutation with excellent penetrance and expressivity. Ms. Ruth Hessler, a student of Samuel Postlethwait, studied ear and tassel development in Fas/+ plants in comparison to their nonmutant sibs, but the results have not been published. Since we are unable to locate Ms. Hessler, there will not be a formal publication, but the increasing interest in studying maize development impels us to note the existence of this mutation and to describe the salient features of its expression.

The vegetative shoot apex of fascicled ear plants does not differ from that of nonmutant plants, but at the transition from a vegetative to a floral meristem, the meristem broadens until the width is double its height. The increase in width is followed by a division into two meristems that then broaden in width. The dichotomous branching is repeated (Fig. 1). Before the process ceases (when spikelet and floret development is initiated), as many as 14 branches may be produced. It is possible that the mutation induces an upset in timing since the appearance of the meristems before division is reminiscent of a branch primordium before division to produce the two spikelet primordia giving rise to the double rows of florets on the cob axis. The product of this deviation from normal development is an ear in which a number of slender ears surround a depressed central area (Fig. 2). The apices of these branches may complete development in a normal fashion or may reinitiate cycles of rapid division producing a fasciated apex. The number of branches may differ from plant to plant within a progeny or even from ear to ear on the same plant.

Fewer kernels as a percent of ovules present mature on Fas ears than on their nonmutant sibs. The abortive kernels are usually on the inner surfaces of the branches.

Well-developed staminate structures that produce mature pollen typically terminate the branches.

As might be expected, the tassel of Fas plants is also affected. As tassel development commences, the apical meristem broadens and then divides. There may be several more divisions producing a highly branched central spike, and Fas plants can be first identified by the tassel morphology. The development of the Fas tassel further parallels ear development in that the branches on the central spike complete development normally.

Seed of this mutant will be sent to the Coop and can also be obtained from Oliver Nelson.


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