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THE INDUCTION OF POLYPLOIDY
IN NICOTIANA SPECIES AND
SPECIES HYBRIDS
By Treatment with Colchicine
HAROLD H. SMITH
Bureau of Plant Industry, U. S. Department of Agriculture
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DIPLOID AND INDUCED POLYPLOID FORMS OF NICOTIANA GLAUCA
Frontispiece
Leaves, stomata and plant habits of the diploid (vertical column A) and of polyploids
Nos. 17, 14 and 15 (columns B, C and 1 respectively). The polyploids had thicker, differently-
shaped leaves, and the stomata were larger and more widely-spaced than in the diploids. Poly-
ploids Nos. 14 and 17 both had 4n chromosomes in the pollen-mother cells-two sets from each
parent species. The marked differences between these two polyploids apparently were due to
the fact that the epidermal tissue, and possibly deeper layers, of No. 17 had a chromosome
number higher than 4n. The diploid plant pictured here is younger than the polyploids and
should be taller for true comparison.
T HE problem of polyploidy in the
genus Nicotiana has been of inter-
est for some time, especially in
relation to the formation of fertile allo-
tetraploids from species crosses. Chro-
mosome doubling has resulted from hy-
bridization1'11 and by use of the follow-
ing artificial treatments: chloroform,2
x-ray,3 bacteria,10 centrifuging,7 growing
shoots from callus tissue formed by
growth hormones6' 12 and, most recently,
by colchicine.
In a preliminary report, Warmke and
Blakeslee19 stated that 51 per cent of the
mature plants grown from colchicine
treated seed of N. Sanderae had tetra-
ploid characteristics. The growing point
of seedlings of the sterile F1 tabacumm X
glutinosa), were treated by them with a
lanolin-colchicine emulsion and 13 per
cent produced branches with a higher
percentage of good pollen than the un-
treated hybrids. Some set seed indicating
that the sterile hybrid had been trans-
ferred into a fertile allotetraploid.
Kostoff8 has published the following
statement concerning his results with
colchicine treatments on tobacco: "Ap-
plying colchicine solution I obtained
tetraploid plants from Nicotiana rustica,
N. tabacum, N. glauca, N. suaveolens,
N. rmegalosiphon, N. velutina, N. alata-
Sanderae, N. suaveolens-alata, . . . and
octoploid in N. alata-Sanderae." Some
of these were described in a more recent
article.9'^
The data reported in this paper deal
with experiments begun in October,
1937, on some Nicotiana species and hy-
brids for the purpose of investigating the
use of colchicine and studying the nature
of the polyploids produced.
Material, Methods, and Results
1. Seed Treatment
Mature p)olyploid plants of Nicotiana
glauca, N. tabacum, F (tabacum X
glauca), and a species hybrid segregant
derived from crosses between N. rustica
and N. tabacum have been raised from
seed treated with 0.2, 0.4, and 0.8 per
cent colchicine for periods of 7, 10, and
14 days. The treatments consisted of
keeping a small amount of seed in about
two cc. of a water solution of the speci-
fied concentrations of colchicine for the
three different periods of time.
Controls of dry seed were planted for
each treated lot. A second control in
which the seed were soaked in water for
seven days, corresponding to the seven
day colchicine treatment, was made on
N. Langsdorffi, F1 (tabacum X sylves-
tris) and F1 (tabacum X glauca). Soak-
ing, in water only, reduced the germina-
tion of Lang sdorffi and the F1 (tabacum
X sylvestris) from 80 per cent to 10 per
cent. Germination of seed of F1 (ta-
bacuin X glauca) was not appreciably re-
duced by the water soaking, a fact which
may partly account for the better results
obtained with this type.
In a preliminary experiment only the
strongest dosage, 0.8 per cent for 14
days, was tried on three different spe-
cies and eight species hybrids. This
treatment affected almost all the plants
that came up; but was generally so
severe that germination was greatly re-
duced and the seedlings were unable to
develop roots or stem growing points.
The swelling and stunting caused by 14-
day treatments with 0.2 and 0.8 per cent
colchicine are illustrated in Figure 1.
Four affected seedlings of N. glauca
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