Effects
of irradiating corn assels with slow neutrons.
Work is in progress in our laboratory on determining the genetical and cytological effects of irradiating maize pollen with slow neutrons. The work has been under way for two years.
Seed for these tests was furnished by Dr. L. J.
Stadler. The female plants were of the genotype aaprprsusu and the male plants
of the genotype AAPrPrSuSu.
In 1947, the corn for irradiation was grown at the
Agricultural Experiment Station, Lincoln, Nebraska, and in 1948 at the Pfister
Associated Growers corn breeding nursery, Naperville, Illinois. In addition,
tassels for the 1947 tests were secured from Dr. C. R. Burnham at St. Paul,
Minnesota. Irradiations were made by placing the tassels in the thermal‑neutron
column of the heavy water pile at the Argonne National Laboratory in Chicago.
The flux was 7 x 1010 neutrons per square centimeter per second at
the position of the tassels. In the 1948 tests, an X‑ray treatment of
1200 r units was also included for comparison.
Table I. Mutations affecting the entire F1
aleurone or endosperm of individual kernels with respect to three marked loci
and percentages of defective kernels from crosses of aaprprsusu plants by
AAPrPrSuSu plants, the tassels of which were irradiated with slow neutrons1
or X‑rays.
|
|
A
locus |
Pr
locus |
Su
locus |
Kernel
development |
||||
|
Treatment |
Total
no. Kernels examined |
Per
cent Kernels colorless |
Total
no. Kernels examined |
Per
cent Kernels red |
Total
no. Kernels examined |
Per
cent Kernels sugary |
Total
no. Kernels examined |
Per
cent Kernels defective |
|
|
|
|
|
|
|
|
|
|
|
Control |
11,326 |
.10 |
11,178 |
.02 |
11,320 |
.01 |
11,380 |
.55 |
|
X‑ray
(1200 r)2 |
6,544 |
5.64 |
5,923 |
.86 |
6,081 |
3.26 |
6,690 |
8.97 |
|
Neutrons |
|
|
|
|
|
|
|
|
|
1/2
minute2 |
3,167 |
.95 |
3,131 |
.10 |
3,166 |
.44 |
3,246 |
2.34 |
|
1
minute |
8,244 |
.82 |
8,160 |
.12 |
8,261 |
.46 |
8,470 |
2.42 |
|
2
minutes |
9,308 |
4.33 |
8,777 |
.89 |
9,164 |
2.38 |
9,992 |
8.30 |
|
4
minutes |
6,203 |
8.83 |
5,484 |
1.51 |
5,522 |
4.45 |
7,761 |
28.93 |
|
8
minutes |
1,925 |
13.04 |
1,660 |
1.45 |
1,515 |
5.61 |
3,335 |
54.81 |
|
16
minutes3 |
47 |
25.53 |
35 |
0 |
49 |
12.24 |
208 |
76.44 |
1Flux
was 7 x 1010 neutrons per square centimeter per second.
2Data
from 1948 crop only.
3Data
from 1947 crop only.
Table 2. Mutations
(chimeras) affecting sections of the F1 aleurone or endosperm of
individual kernels with respect to three marked loci and percentages of kernels
with sections defective in development, from crosses of aaprprsusu plants by
AAPrPrSuSu plants, the tassels of which were irradiated with slow neutrons or X‑rays.
|
|
A
locus |
Pr
locus |
Su
locus |
Kernel
development |
||||
|
Treatments |
Total
no. kernels examined |
Per
cent kernels mosaic
for colorless |
Total
no. kernels examined |
Per
cent kernels mosaic
for red |
Total
no. kernels examined |
Per
cent kernels mosaic
for sugary |
Total
no. kernels examined |
Per
cent kernels mosaic
for defective |
|
|
||||||||
|
Control |
11,314 |
1.24 |
11,176 |
.10 |
11,319 |
.03 |
10,217 |
.04 |
|
X‑ray
(1200 r)2 |
6,176 |
1.39 |
5,874 |
.37 |
5,883 |
.34 |
6,090 |
.20 |
|
Neutrons |
||||||||
|
1/2
minute2 |
3,137 |
1.20 |
3,128 |
.19 |
3,152 |
.16 |
3,170 |
.06 |
|
1
minute |
8,176 |
1.38 |
8,149 |
.23 |
8,225 |
.11 |
7,431 |
.04 |
|
2
minutes |
8,904 |
2.56 |
8,699 |
.37 |
9,018 |
.22 |
6,671 |
.24 |
|
4
minutes |
5,659 |
2.36 |
5,466 |
.58 |
5,286 |
.38 |
4,931 |
.52 |
|
8
minutes |
1,675 |
4.12 |
1,636 |
.91 |
1,430 |
.83 |
1,113 |
1.42 |
|
16
minutes3 |
35 |
2.78 |
35 |
0 |
49 |
0 |
-- |
-- |
1Flux
was 7 x 1010 neutrons per square centimeter per second.
2Data
from 1948 crop only.
3Data
from 1947 crop only.
Observations on mutations affecting the entire F1
aleurone or endosperm of individual kernels with respect to the three marked
loci for the various treatments are presented in table 1. Percentages of
kernels with the F1 tissue defective in development, as determined
by external appearance of the caryopsis as a whole, are also shown for the
various treatments.
Mutations involving the same characters but
affecting only sections of individual kernels (chimeras) are reported in table
2.
The F1 generation from seed produced in
1947 was grown at Lincoln in 1948. Plantings were made directly in the field on
May 21 and June 8, except that at the first planting date the defective seeds
were planted in the greenhouse. The results from this planting in the greenhouse
are not included because of rodent injury. Combined data on stands from the
various treatments for the two planting dates are presented in table 3.
Table
3. Stand of F1 plants from crosses of normal by normal with tassels
irradiated at various lengths of time with slow neutrons. Combined data from
plantings made at Lincoln, Nebraska, on May 21 and June 8, 1948.
|
Length of time tassels
exposed to neutron irradiation |
No. of kernels planted |
Stand of plants |
|
|
No. |
Per cent |
||
|
|
|||
|
Control |
279 |
256 |
91.8 |
|
1 minute |
337 |
297 |
88.1 |
|
2 minutes |
346 |
286 |
82.7 |
|
4 minutes |
429 |
206 |
48.0 |
|
8 minutes |
328 |
101 |
30.8 |
|
16 minutes |
38 |
2 |
5.3 |
E.
F. Frolik and
Rosalind
Morris