Tassel plant of maize
--Ting, YC and Nguyen, DQ

It is known that morphogenesis of inflorescences of flowering plants is under genic control. Whenever a controlling gene(s) is turned on by induction factors, low temperature, ionizing radiation etc., the developmental pathway is normally as follows: the vegetative meristem gives rise to inflorescence meristem. In turn, the inflorescence meristem is transformed into floral meristem. Then, the floral meristem develops into floral parts. This is also true for maize. However, if an intrinsic developmental factor involved in the regulation of floral initiation is inactivated, maize floral development can be arrested. The following is an example of this altered development.

In the last summer, among a row of semi-perennial maize, one plant was particularly vigorous and bore more tillers than the others. However, it was slow in development. When the tassel of this plant emerged, it appeared strong and pendant, and its antheses were totally aborted. In consequence of this, many plantlets, starting from the proximal portion, grew out from the tassel of the main stalk (culm). By a single count, 78 of them were scored. Under close examination of these plantlets, it appeared that they originated from paired spikelets (Figure 1). Subsequently, this plant was tentatively designated tassel plant, or Tpl for short. In addition, some variations, such as in plant color and growth pattern among the plantlets, were observed, indicating segregation occurring during meiosis. This suggests that the plantlets might differentiate from the microspores. Nonetheless, this can not be ascertained until their chromosome number is determined.
 
Figure 1. Plantlets of a tassel plant. Size reduced by about 50 percent.

When the plantlets had reached about two weeks old, two-dozen of them were removed from the tassel and planted in pots in the greenhouse. About 50 percent of these transplanted plantlets continued to grow into large normal plants while the others reverted into pistillate flowers. Cross-fertilizations were attempted between these flowers and the sib tetraploid, but no seed sets were obtained. On the other hand, those plantlets left on the main tassel also continued to grow. Later about 10 percent of them also reverted to pistillate flowers with two or more silks.  

Cross-fertilizations were also attempted, but no viable seeds were found. The rest of the plantlets continued to grow to four to five-leaf stage. Then, they withered and died.

One of the above plant's tillers grown from the basal node also had a larger than average tassel. In addition to having more than 50 plantlets developed, it had a few antheses. Then they were followed by dehiscence. Consequently, its pollen was applied to silks of one half of its ear, and those of the other half were outcrossed to a sib (4n). At harvest, 73 well-developed kernels were obtained. Presumably one half of them developed from selfings, and the other, from crossings. There are now more than 10 plants descended from both selfings and crossings, growing in the greenhouse. These plants are normal in phenotypic appearance and are growing well. A planned genetic as well as tissue culture investigation is under way with these plants. 


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