8. Dwarf and short plants.


a. Classification of genes controlling reduced plant, height was continued on a considerable scale during the 1950 season. Twenty-six stocks carrying unidentified and unlocated dwarfing genes were grown. Some of these stocks ("Oakes dwarf," "Hy dwarf," "R4 dwarf" and others) have previously been described in the Maize News Letter; others are new.


b. The designation brachytic‑2 (br-2 is suggested for the major gene controlling reduced internode length in the "Oakes dwarf" and "R4 dwarf" stocks. This mutant gene is opparently of rather freauent independent occurrence, since Singleton reports several additional stocks which carry it. "Oakes dwarf" and "R4 dwarf" differ phenotypically in that the former has all internodes greatly shortened, while the "R4 dwarf" and related stocks ("Hahn 6" and others) have short internodes only below the ear. The F1 between the two stocks shows the same internode length pattern as "R4 dwarf." It thus appears that one major gene and one or more modifiers are involved, though we cannot at present exclude the possibility of multiple allelomorphism. F2 data are so far inconclusive.


c. Six new short mutants, five of which were found in standard inbred lines, have been found to be genetically different from br-1, br-2, Singleton's rd, and the "Hy dwarf" gene. Further tests are in progress.


d. F2 of "W8 dwarf" x br2 shows a segregation of 13 apparently normal: 3 "W8 dwarf" type in the seedling stage. "W8 dwarf" type segregates can easily be classified in this stage, since elongation of the leaf sheaths is greatly reduced. At maturity, normal height plants, both short types and the double dwarf can be classified, giving a close fit to a 9 : 3 : 3 : 1 ratio.


e. Both "W8 dwarf" and "O7 dwarf" type segregates can easily be classified in the seedling stage F2 populations of both these mutants with multiple-chromosome testers from Stadler and Mangelsdorf have been studied intensively in the greenhouse this winter. The "W8 dwarf" gene is quite definitely not linked with lg-1. (Chrom. 2), a (Chrom. 3), gl1 (Chrom. 7) or g1 (Chrom. 10). There is a possibility that it is loosely linked with su1 (Chrom. 4), but more precise tests are needed.


Earl R. Leng and M.L. Vineyard