Flores-Reyes, I., and C. M. Rick.
The production by colchicine of true-breeding lines that differ genetically from controls has been reported by several workers. They attribute this unusual phenomenon to a series of colchicine effects: (1) reduction to haploid chromosome number, (2) induction of mutation, (3) doubling of chromosome number by the usual colchicine action. Chronologically the first step could be either No. 1 or No. 2, but No. 3 would have to be last.
Tomato material that was treated for another purpose in the 1958 season provided a good opportunity to search for this kind of colchicine response. The material consisted of two lines of F1 hybrids, one heterozygous for ah, yv, and dl, the other for MacArthur's stock, a\l, c, d\l, and l\l. Colchicine (0.5%) was applied in lanolin emulsion to the terminal growing point and leaf axils of 20-day seedlings growing vigorously under greenhouse conditions. One, two, and three-day applications were made, but the single application was sufficient to induce polyploidy. The plants were later transplanted to the field in the usual fashion. Some measure of the penetration and influence of the treatment is given by the fact that approximately half of the branches of treated plants were 4N.
The first 20 plants of each line were allocated to this experiment. Each plant was pruned to four main branches, which were inspected frequently throughout the season. Pollen samples were examined as an assay of chromosome number and phenotypic expression was observed, particularly for the characters for which the plants were known to be heterozygous. Fruits were harvested and seeds extracted separately for each diploid branch. These seeds were then sown and the seedlings scored for the respective characters. To date 88 progenies of 20-25 seedlings apiece have been processed in this manner.
Seemingly the material in this experiment would afford a better opportunity than pure lines for testing the homozygotizing effect of colchicine because a response could be observed without the occurrence of mutation (step 2). Nevertheless, no phenotypic manifestation of any of the genes was seen in branches of the treated plants except for the usual heterozygous expression of d\1 (slight roughening of the leaf surface). The progeny tests are summarized in the following table. Each progeny segregated for the genes anticipated from its pedigree. The Chi-squares indicate a significant deviation from 3:1 only for c, and give no significant indications of heterogeneity between families. The data therefore give no suggestion of a homozygotizing effect of colchicine treatment.
Total Deviation Heterogeneity
Family Gene Chi-square Chi-square d.f. Chi-square d.f.
419 a\1 21.59 0.109 1 21.48 50
d\1 20.77 0.0002 1 20.77 50
c 29.09 7.O9** 1 22.00 50
421 yv 28.37 1.83 1 26.44 36
ah 14.73 0.0002 1 14.73 36
dl* 4.60 0.067 1 4.53 14
* segregations for dl were not scored in some of the progenies.
** significant at the 1% level.