Chestnut Hill, Massachusetts
Boston College
More studies of day length effect on cloning gene in tetraploid maize --Ting, YC and Tran, L In order to find out how short-day illumination (12 hrs or less) affects the expression of cloning gene in tetraploid maize (Zea mays L.), several tests were conducted in the last few years. Descriptions of these tests follow:--In July of 1999, a short-day treatment was applied to 11 adult plants heterozygous for the cloning gene (Clg clg clg clg), by covering them with black plastic barrels from 6:00 PM to 10:00 AM the next day. At that time, those plants were a little over three months old and their male inflorescences just began to initiate. The treatment continued for three months. One month after the treatment was discontinued, contrary to expectation, none of the treated plants responded positively by regenerating tassel plantlets. However, three of the control-plants having the same genetic background manifested a weak expression of plantlet regeneration by growing out three to five plantlets per tassel. It was intriguing! When those control-plants showing regeneration were sib-crossed, many well developed kernels were obtained. Therefore, it was deemed necessary to make another test on the transmission of the cloning gene. Subsequently, in early November of the year 2000, 12 selected kernels of one of the above parental plants were sown in the greenhouse. In the first week of February of this year, the same number of kernels of another parental plant were sown next to the first planting. Last May, it was observed that six adult plants of the first planting were healthy and well developed, and four of the second planting did as well. About three weeks later, it was surprising to find that only one of six of the first group and two of the second responded respectively by regenerating vigorous tassel plantlets. Figure 1 depicts one of the tassels bearing many plantlets. This plant was one of the pedigree plants of the fifth generation of cloning gene transmission. In the middle of last June, a further test on the behavior of the cloning gene was carried out. Of each of the above positive respondents, 10 plantlets were detached and planted in the summer experimental plot. The plantlets were at the three- to four-leaf stage in development. In the first week of July, it was found that one of the plantlets grew to about two feet tall and regenerated plantlets. However, in contrast, all of the other plantlets continued to develop into normal adult plants and, on average, they reached about six feet in height two months later. They all failed to regenerate plantlets. The above plantlet transmission experiment was conducted under long-day (more than 12 hrs) condition, from the time of their initiation to the stage of their seed maturation. Up to the present, it appears that a tentative conclusion can be drawn on the inheritance of the cloning gene in the tetraploid, starchy and semiperennial maize. It is dominant. The expression of its phenotype was more likely to be affected by day length; short day was more effective in the induction of plantlet regeneration than long day. Nevertheless, under a short day regime, the stage of plant growth may play a certain role in the sensitivity of the cloning gene to day length.

Figure 1.

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