EARLY INFLORESCENCE AND FLORAL DEVELOPMENT IN ZEA DIPLOPERENNIS, DIPLOPERENNIAL TEOSINTE

Abstract

This study uses SEM and LM to investigate the ontogeny and histogenesis of the tassel and ear spikes, spikelets and florets of diploperennial teosinte, Zea diploperennis litis, Doebley, and Guzman. The pattern of development observed in this teosinte is compared to the literature descriptions of corresponding development in Zea mays L. The data indicate two distinct developmental patterns in teosinte: one characteristic of the male and mixed inflorescences; the other the female inflorescence. The branching pattern we observed in male and mixed inflorescences of diploperennial teosinte is identical to that described in both the male and female inflorescences of Z. mays. The initial primordium, a bract produced along the primary axis, subtends an axillary branch which bifurcates unequally, forming two spikelets, pedicellate and sessile. The sessile spikelet is interpreted as a branch of the pedicellate spikelet. The first bract produced on each spikelet is the outer glume. The developmental pattern of a mixed inflorescence shows a transition from distichous four‐rowed staminate spikelets to distichous two‐rowed cupulate fruitcases. At the transition node, a staminate pedicellate spikelet and a pistillate sessile spikelet is observed. In the pistillate spikelet, the outer glume becomes part of the cupulate fruitcase. In the female inflorescence, only a single spikelet forms in the axil of the initial primordium: the axillary branch primordium becomes the spikelet apex; and the initial primordium becomes the outer glume, eventually a part of the cupulate fruitcase. The first bract produced by the spikelet apical meristem is the inner glume. There is only one observable spikelet and no recognizable rudimentary spikelet, pedicellate or sessile. Therefore, while the cupulate fruitcases of female and mixed inflorescences appear identical at maturity, they do not have the same ontogeny. The evidence supports a hypothesis that the progenitor of a Z. mays ear may be a mixed teosinte inflorescence rather than a pure male tassel or pure female spike. The developmental morphology of male and female inflorescences of other Zea species should be examined.