11.
Row number studies.
Variability within inbred lines of maize has long
been observed. Hy2 and R4 are highly variable, while many other lines are
relatively uniform. Dr. R. A. Emerson's work has pointed out that environmental
conditions may affect row number.
In 1946 approximately 40 ears were selected from
standard selfed material of each of the inbred lines, Iowa L289, Indiana WF9,
Illinois 90, Illinois R4, and U.S.D.A. C.I. 187‑2. No effort was made to
select for row number when these ears were picked out. These were "ear
hilled" in 1947, "ear rowed" in 1948, and "ear hilled"
again in 1949.
Replicated, randomized block plantings were made of
some of these sub‑lines in 1948 and 1949. In all five inbreds studied,
highly significant differences existed between the means of certain sub-lines.
Extreme differences as observed during the past growing season are indicated in
table 1.
Table 1. Primordia*
number of inbred lines
|
Inbred |
High row number |
Low row number sub‑line (X) |
Primordia number required for significance (1%
level) |
|
L289 |
5.98 |
5.77 |
.08 |
|
WF9 |
8.94 |
7.67 |
.22 |
|
90 |
10.87 |
10.41 |
.40 |
|
R4 |
9.16 |
8.50 |
.39 |
|
187‑2 |
8.44 |
6.97 |
.23 |
*
Row number equals primordia number x 2.
Statistically significant differences exist between
means of the F1 crosses of sub‑lines when crossed on to the
same tester, i.e., a sub‑line of another inbred. F2 and
backcross data are inconclusive, although in some cases, these means too are
significantly different.
Studies were made over a two‑year period on
intra‑plant variation in row number within three inbred lines, and their
three possible single crosses. Mean values of these are indicated below. Node 1
is the uppermost ear‑bearing node, node 5, the lowermost node studied.
Table 2. Primordia
number at successive nodes
|
|
Node |
||||
|
Pedigree |
1 |
2 |
3 |
4 |
5 |
|
L289‑22B |
6.12 |
6.08 |
5.43 |
4.91 |
5.10 |
|
WF9‑24 |
8.56 |
9.00 |
8.75 |
8.44 |
8.78 |
|
90‑4 |
11.89 |
11.19 |
10.42 |
9.64 |
9.08 |
|
|
|
|
|
|
|
|
L289 x 90 |
8.07 |
7.27 |
7.03 |
6.64 |
6.45 |
|
L289 x WF9 |
7.43 |
7.00 |
6.91 |
6.59 |
6.48 |
|
WF9 x 90 |
10.41 |
10.14 |
9.52 |
9.03 |
8.89 |
It appears that the later differentiated ears
possess higher row number than those differentiated when the plant is smaller,
except in the case of WF9, where no such gradation exists.
An attempt was made to evaluate to what degree non‑genetic
factors would affect row number. Inbred and hybrid plants were cut off slightly
above ground level shortly after their emergence. This treatment was continued
for varying lengths of time, usually until some of the plantings died. Counts
of row numbers at each of the five nodes indicate that this treatment was
highly effective in reducing row number. The magnitude of this reduction was
highly variable, but in all observed cases, positive.
It appears likely that at least some of the commonly
used inbred lines are genetically heterogeneous for row number, and that
selection can shift the mean row number normally associated with that line.
D. E. Alexander