Hermaphrodite florets in a derivative of a corn x teosinte hybrid

Individual florets from corn, teosinte and Tripsacum inflorescences are typically unisexual. Although the tassel-seed mutants in corn produce part male, part female inflorescences, the individual florets are either male or female--not hermaphrodite. The material to be described arose from a complex parentage involving two marker stocks of corn (tassel-seed, Ts5, and unbranched, ub), a primitive popcorn from the Maize Collection identified as Argentine Altiplano 548, and a Mexican race of teosinte, "El Salado." Teosinte was used only as a male parent during the breeding procedure:

(Ts5 x Altiplano) x teosinte. A tassel-seed type extracted from this cross was selfed to provide Parent A.

(ub x teosinte). This hybrid was selfed and a homozygote, ub ub, extracted in F2 to provide Parent B.

Parent A was heterozygous for tassel-seed; Parent B was homozygous for unbranched. A small progeny from the F2, A x B, segregated for tassel-seed and what was, supposedly, a modified variant of unbranched (i.e., tassels with a main axis and only 2-3 laterals). Among the segregates was a new type, having the gross morphology and exterior spikelet morphology of a normal corn tassel, except that silks emerged from nearly all the spikelets. It was thought, at first, that all the spikelets had been converted completely from male to female, without the usual condensation and rachis enlargement associated with tassel-seed. Accordingly, the "tassel" was outpollinated in an attempt to set seeds. Ten to twelve days after pollination the developing caryopses began to protrude through the sterile glumes and concomitantly anthers were extruded and began to shed a limited amount of pollen. Careful dissection of the spikelets showed that the basal floret in most spikelets was hermaphrodite. It included all the normal structures of a male floret (glumes, paleas, three anthers) and in addition a developing caryopsis with the withered base of the silk still attached (see text figure). The upper floret in each spikelet was normal (i.e. unisexual, male). Spikelets located toward the extremities of the tassel branches were entirely male. Although the anthers shed a limited amount of pollen, and the pollen grains appear normal under microscopic examination, it is not yet known to what extent they are viable. In any event, the plant is completely self-sterile because of its strong protogyny. The development of axillary branches (ear shoots) is much delayed and no silks have emerged to date.

Figure.

S. G. Stephens


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