Since the writing of our last research report (Plant Sci. Lett. 23:139-145, 1981), more experiments on maize anther culture in vitro were carried out. The medium employed was also zheng-14 and the materials were maize Dan-Sun 91 and its derivatives. Anthers, approximately 5000 in number, were inoculated. It was found that the average response, in terms of callus initiation and embryoid growth, was about 15 percent. More than 50 percent of the embryoids could grow into plantlets without any change of plant hormones in the medium. Out of the calli, 15 new lines were established. Seven of these new lines have been subcultured and maintained in the culture room for several months.

Regenerated plantlets, however, varied widely in their gross morphology. It was difficult to determine whether these variations were brought about by mutations or by adverse environments. Over 50 percent of them manifested a certain degree of chlorophyll deficiency. When they grew in the greenhouse during winter, they produced predominantly pistillate inflorescences. Fully developed kernels were occasionally obtained upon crossing these haploid plants with pollen from diploid Wilbur's Flint. Nevertheless, the percent of seed set was very low.

When male inflorescences of Dan-Sun 91 were immersed in 2,4-D solution (10 mg/l) for 6 h before inoculation, the treatment failed to yield higher percent of response to culturing than the control. This is very different from the experimental results with tomato anther culture. When pretreatment with 2,4-D was carried out, it consistently yielded better response to culturing.

It was also observed that during callus and embryoid initiations as many as 5 points of growth were found for a single anther. These growth points could exclusively lead to the development of embryoids or to the development of calli, or to the development of both calli and embryoids. There was no evidence of preference for any of them.

In order to have a high percent of survival in transplanting haploid plantlets from culture medium to the greenhouse, it was important to autoclave the soil. Furthermore, the newly transferred plantlets should be provided with 60 percent humidity, a day temperature of 65 to 70 F, and a night temperature of 55 to 60 F. Under these conditions, we obtained as high as 45 percent survival.

Margaret Yu and Y. C. Ting

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