Sustained treatment with gibberellic acid of maize plants carrying one of the dominant genes teopod and corn-grass.

NICKERSON, NORTON H. (Washington U., St. Louis, Missouri.) Sustained treatment with gibberellic acid of maize plants carrying one of the dominant genes Teopod and Corn-grass. Amer. Jour. Bot. 47(10): 809-815. Illus. 1960.-Groups of field-grown plants of 2 dominant maize mutants, Corn-grass (Cg) and Teopod (Tp), were treated with either distilled water or with 1 of 3 concentrations of aqueous gibberellic acid (GA) every 3 days from the seedling stage until tassel emergence. Both dominant mutants were found to respond to GA in such manner that certain treated plants became essentially normal in phenotype. The role of GA in modifying expression of specific genes is briefly discussed. EFFECTS of gibberellic acid on different plants are being reported with increasing frequency. Stowe and Yamaki (1957) presented the first complete review; recently (1959) they have made a short but up-to-date survey. Brian (1959) has covered recent literature more thoroughly and has made an attempt to integrate some of the seemingly controversial effects reported. The first instance in which plants of known genotype were phenotypically modified by external application of gibberellic acid (hereinafter called GA) was reported by Phinney (1956) in his work with maize. Brian and Hemming (1955) also obtained a similar reaction to GA by dwarf peas, but the peas they employed were a commercial variety of unilknown genotype. Other work by Plummer and Tomes (1957) on dwarf tomatoes, by Cooper (1958) oni dwarf perennial rye-grass (Lolium), and by Irvinie and Freyre (1960) on dwarf Tephrosia has shown that gibberellic acid could overcome effects of these specific recessive genes such that treated plants in each case assuLmed proportions of normal plants. All the instances cited involved recessive genes; this paper deals with effects of GA on 2 dominant genes found in maize, Corn-grass (Cg) and Teopod (Tp). Both these genes may be reduced in expression by appropriate treatment with GA to the point where plants that carry them are essentially normal in appearance. MATERIALS AND METHODS.-A limited supply of seed2 of the 2 stocks containing these genes was planted on June 20, 1958. Both samples were derived from open-pollinated ears, but plants were in such positions in the field that pollen available was only from siblings. Each of the seed stocks was shelled from a single ear which exhibited the genetic clharacter being investigated. Germination 'Received for publication MIay 18, 1959. This work was part of a research program carried out during the summer of 1958 while the author held a National Science Foundation Science Faculty Fellowship. Thanks are extended to Dr. B. 0. Phinney who kindly consented to review this manuscript. 2 Seed stocks were kindly supplied by Dr. William L. Browni, Pioneer Hi-Bred Corn Company, Johnston, Iowa. was nearly 100%. Each of the 2 stands of seedlings was divided into 4 equal groups. Each Cg group contained 9 plants; each Tp group contained 17 plants. On July 9, about 2 wk. after germination, young plants had 3-4 leaves, and treatments were begun. Each third day thereafter, until tassel emergenice, 1 ml. of distilled water only for control plants and for others 1 ml. of distilled water containing a particular concentration of GA 3 was administered to each of the respective apical leaf cavities. A total of 14 treatments was administered before tassel emergence. In cases where excessive tillers developed, only the original main leaf cavity was treated. Treatments are summarized in table 1. The groups were not randomized, but another experiment in the same field (Nickerson, 1959) showed conclusively that results obtained with identical concentrations of GA were independent of field location for any particular strain of maize. GA solutions wvere freshly made each week and kept in darkness at 19?C. To eliminate any possible effect of interaction between insecticides, fungicides and GA. no snraving was done either for control of fungi, of which none was noted, or for insects. of which both corn earworm and corn borers were noted. Fertilizer (Agrico 5-10-10) was applied at the rate of 600 lb. per acre during the fourth week after planting. RESULTS. Plants containing the dominant Corngrass gene were found to respond to treatment with GA in direct relation to dosage. The numbers of Cg plants which occurred in each treatment group of 9 plants were 5. 5, 5 and 4 respectively. Tke genotypes of the 'lants are thus assumed to be either +/+ or Cg/+, the combinations to be expected if an ear on a Cg/+ plant were pollinated with pollen produced on a +/+ plant. The results noted below are based on a coromarison of all mutant plants in each group. Each Cg-carrying plant could be easily identified at the third leaf stage by its narrow, glaucous blue-green leaves. 'GA used in this experiment was supplied by courtesy of Dr. Curt Leben, Agricultural Research Division, Eli Lilly & Company, Greenfield, Indiana. rThe JOURNAL for November (47: 713-808) was issued November 14, 1960.1 AMERICAN JOURNAL OF BOTANY, Vol. 47, No. 10. December, 1960