J. Hered. 47(5): 229–233 (1956).
COLCHICINE-INDUCED TRUE-BREEDING CHIMERAL SECTORS IN FLAX
V. A. DIRKS, J. G. ROSS AND D. D. HARPSTEAD*

THE induction by colchicine treatment of homozygous diploid variants in sorghum without change in chromosome number has been reported by Franzke and Ross.5 Ross, Franzke and Schuh8 have demonstrated that agronomically important characteristics in sorghum may be changed as a result of treatment and that the progeny of the changed plants breed true in the majority of cases. As part of a program to investigate the universality of this phenomenon in other biological material, seedlings of flax, soybeans, corn and wheat have been treated with colchicine in the same manner at the South Dakota Station. This study is concerned with the results of treatment of F1 seedlings of crosses between varieties of flax containing gene markers to permit the detection of somatic segregation.7

Materials and Methods

The epicotyls of F1 seedlings from eleven different flax crosses were coated with 0.5 percent colchicine in lanolin as soon as the cotyledons opened. The treated epicotyls formed typical c-tumors, and subsequently new shoots arose from these growths. Since Franzke and Ross5 had noted chimeral effects in sorghum, seed from each of the main branches arising from the c-tumor was kept separate during harvest to permit the identification of possible chimeras. The progenies of the branches were grown in individual progeny rows in 1952 and classified for flower color, rust resistance and other obvious characteristics. Promising material was advanced to yield tests, consisting of four-row rod-row plots in three replications.

Surplus F1 seed of a series of crosses made as part of a flax improvement program was used in this study. Some of these crosses involved a wide range of characters, which would permit recognition of somatic segregation. This report is primarily concerned with the progeny of two of these crosses: (a) Crystal (C.I. 982) x B-5128 (C.I. 980) (b) Crystal (C.I. 982) x Can. 3855B. Crystal is yellow-seeded, white-flowered, tall and wilt resistant, and carries the L factor for rust resistance.8 B-5128 is brown-seeded, blue-flowered, tall, and moderately wilt resistant, and has the N4 gene for rust resistance. Can. 3855B is a brown-seeded, blue-flowered type with the L factor for rust resistance. Brown seed coat is dominant to yellow; blue flowers are dominant to white; the genes for seed-coat color and for flower color are linked. Plants with either the N4 or L gene or both are resistant to the Race 180 of Melampsora lini (Pers.) Lev. prevalent in the Brookings area in 1953, while plants without at least one of these genes are susceptible.

Observations and Discussion

When treated plants were harvested it was noted that in one F1 plant of the cross Crystal x B-5128, branches differed in the color of seed produced. Branches 1, 2 and 3 had only brown seed; branches 4 and 5, only yellow seed; branch 6, a mixture of yellow and brown seed. Seed harvested from each of these branches is shown in Figure 18, arranged around seeds from an untreated F2 plant. Seed from the sixth branch of the original plant was separated into yellow (6a) and brown (6b) fractions. In 1952, each lot of seed from the separated fractions and from each of the first five branches produced F3 plants uniform within each lot for seed color, flower color, height, general plant type, and rust resistance. The true-breeding nature of these progenies in the next three generations was established by observations at Brookings in 1953, 1954 and 1955 (Table 1). Mean yields taken during these three years indicated that as a group, the brown-seeded branches significantly out-yielded the yellow-seeded branches during this period. They out-performed the yellow ...

Somatic Segregation Biblio