Spontaneous mutations.

Four different spontaneously‑occurring mutations in maize have been noted in the course of the genetics studies at Nebraska. All trace to lines secured from Dr. John H. Lonnquist's breeding material. These matters have been temporarily designated dp‑Nl, pg‑Nl, v‑Nl, and bt₁‑Nl. We will be glad to furnish seed carrying these mutations to anyone on request.

dp‑Nl. This mutant appeared in the F₂ from crosses of CC5 x recovered L289. The tassels of a portion of the plants had been irradiated. Fifty‑six of 103 F₂ families segregated for an abnormal type of plant, designated dp-Nl. Since the mutant plants occurred independently of treatment, including occurrence in some of the control cultures, the possibility of an irradiation‑induced mutation is excluded.

Segregation for dp‑Nl within a family varied from 1 in 4 plants to 1 in 18 plants with 98 abnormal plants in a total of 967 plants. At maturity, height of the mutant plants varied from 1/6 of the height of the normal sibs to almost normal height. The leaves were uniformly narrower and darker green than normal, with necrotic edges which frayed, giving a slashed appearance. The reproductive organs varied from plants producing both tassel and ear shoot to those lacking both. The tassels were small and bunched, but a superficial examination indicated that pollen was normal. Very limited cytological observations indicated the following: the various stages of meiosis were all present, but there was considerable deviation from the normal‑behavior of chromosomes. Some of the abnormalities observed were stickiness of chromosomes, delayed cell division, and aberrant spindle formation at meiosis II. Nevertheless, the resulting microspores and young pollen grains appeared normal for the most part.

pg‑Nl. In the same material as that in which dp‑Nl appeared, but confined to the 4‑minute nuclear‑reactor treatment, approximately half of the families segregated for a yellow‑green plant. The mutant plants died in an early stage of development. Segregating ratios within individual families were variable, but the 134 plants from the combined progenies gave a good fit to a ratio of 3 normal to 1 mutant. The possibility that the mutation was due to the treatment is remote since each of the 9 segregating families would have had to trace to the simultaneous occurrence of the same mutation in 9 different pollen grains. Neither could the mutation have been present in the male parent since the same plant was used in all the treatments. On the other hand, different plants were used as female for each treatment and they were descended from bulk selfed seed. The plant used as female parent in the 4-minute treatment must have been heterozygous for the recessive gene yg‑Nl. It is possible that the mutant plant may be due to one of the pg alleles which is lethal in its effect.

v‑Nl. This virescent can be traced to the heterozygous condition in a recovered L289 plant from selfed seed grown in 1948. In 5 segregating cultures grown in 1950, there was a good fit for a 3 normal : 1 mutant ratio for the entire population.

This mutation has a rather severe effect on the plant throughout its development. In addition to the virescent condition in the seedling stage the plants were noted to be about one‑half as tall as the normal sibs at approximately 30 days and 60 days after planting. The leaves tended to be stiff and narrow toward the tips. At flowering time the plants were about two‑thirds as tall as the normal sibs. The plants produced no kernels, even when allowed to open‑pollinate.

bt₁‑Nl. This mutant occurred in K167, a line from an open‑pollinated, yellow variety. It is conditioned by a single, recessive gene. The endosperm is similar to that described for bt₁. Extremely poor stands have been secured and the mutant plants are very late in flowering. Tests for genetic identity both by us and by Dr. E. G. Anderson at the California Institute of Technology indicate that this brittle is allelic to bt₁.

E.F. Frolik and Rosalind Morris