During the 1948 season 100 monoploid maize plants were obtained, all of maternal origin. Of these, 43 were from dent corns, 53 from sweet corns and 4 from genetic stocks. The average frequency of occurrence was about 1/900 in the dent corns and 1/375 in the sweet. Twenty‑eight of the sweet corn monoploids were derived from a sample of 3,814 hybrid kernels of which Robson's Golden Cross Bantam was the seed parent. Ignoring this sample, the average frequency of occurrence in the sweet corns tested was 1/640.
About 1/5 of the monoploids yielded one or more kernels on selfing and about 1/3 set seed upon outcrossing. Most of the pollen used in selfing was obtained from diploid sectors in the tassels of the monoploids. The rate of spontaneous doubling of the chromosome complement in these plants appears to be fairly high, as evidenced by occasional anthers of normal (2n) size, full of viable pollen.
Sectors noted ranged from a part of a single anther to whole florets, tassel branches, and, in one case, the whole tassel. In colchicine treated plants more 2n sectors were noted and the plants yielded about three times as nnany kernels per plant (average, 10 kernels) as the untreated controls an selfing and outcrossing. In cases where only one to three kernels were obtained germination tended to be poor.
In material being examined at present approximately 100 more maternal monoploids have been found and one paternal monoploid. From 300 to 400 monoploid plants should be available for study this season. In addition a number of homozygous lines derived from monoploids are being grown for study and increase.
Sherret S. Chase