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During the past year, grain-to-stover ratios
were used in: (1) a mass selection scheme,
and (2) selection among and within 51 lines.
The germplasm used in the mass selection
study was a composite derived from a cross
between a short early corn, from Antigua in
the Caribbean and a tall Tuxpeno from Mexico.
A program of mass selection in this composite
was started in Poza Rica, Veracruz in
1969, using a selecton intensity of five percent
for plants with the highest grain-to-stover ratio.
The population has undergone three cycles of
mass selection. During the second cycle, some
selection pressure was directed toward lowering
ear height, selecting only those plants with
the uppermost ear below 161 em. for the
grain-to-stover determinations. Badly diseased
or otherwise undesirable plants were de-tasseled
during the third cycle of mass selection.
Progress from the first cycle of selection
was evaluated in the summer of 1969 in a
performance trial with ten replicates. This trial
included: the original population Co; the first
cycle population, C I (Me) from the grain stover
program; and a first cycle population derived
from selection for grain weight per plant C l
(M).
Three plant densities (21,739; 43,478; and
65,217 plants/ha) were used in a split-plot
design. Data were recorded on days-to-silking,
plant and ear height, day-to-pollen shedding,
number of ears-per-100 plants, stover weight,
grain weight, shelling percentage, and percent
of lodged plants.
Mean values and the realized gain for
grain-to-stover ratio and grain yield of the
populations are presented in Table 1. Relative
to the original population, one cycle of
selection resulted in a gain of 2.9 percent in
grain-to-stover ratio at the rate of planting
similar to the one used during selection. Negative
values were obtained when the population
was evaluated at higher plant densities.
The population resulting from selection for
grain yield per plant showed no gain in grainto-stover
ratio at all three plant densities.
It is worth noting that the gains in yield
after one cycle of selection for grain-to-stover
ratio lC I (Me) vs. Co] were 2.2 percent, 2.4
percent, and 6.3 percent at 21,739; 43,478; and
62,517 plants per hectare, respectively. This
seems to indicate that selection for grain-tostover
ratio resulted in considerable improvement
in yield and tolerance to high plant densities.
One cycle of mass selection based on
yield-per-plant lC I (M) vs. Co] produced a
gain of 3.2 percent in grain yield at 21,739
plants per hectare, but there was no gain at
43,478 plants/ha, and a reduction of 4.9 percent
at 65,217 plants/ha.
There were changes associated with the
selection for grain-to-stover ratio in other
agronomic characteristics, also. In general,
the population C I (Me) was earlier, with shorter
plants and lower ears, and better standability
than the original population.
The outstanding feature of the selection for
grain-to-stover ratio seems to be the correlated
responses which enable the resulting
population to be: (1) more productive, (2) more
tolerant to high plant densities, (3) earlier, and
(4) shorter.
Estimation of Heritability and Correlations
with Grain·to-Stover Ratio
Using fifty families showing the highest
grain-to-stover ratio from a mass selection
program for this character, an experiment was
planted in Poza Rica, Veracruz, Mexico, to
estimate the heritability of grain-to-stover ratio
by parent-offspring regression and to compare
simple correlations between grain-to-stover
ratio and eight other characters. These characters
were: plant height, ear height, day-topollen
shedding, days-to-silking, lodged plants,
number of ears, stover weight, and grain
weight.
TABLE 13. Mean values and % realized gain for
grain/stover ratio and grain yield of three Compo
C populations at three planting densities. Poza
Rica, Veracruz, Mexico. 1969.
Grain/stover
Grain yield (kg/ha)
Mean % Gain Mean % Gain
21,739 pl/ha
Co 0.68 0.0 3391 0.0
Cl (Me) 0.70 + 2.9 3467 + 2.2
Cl (M) 0.67 - 1.5 3500 + 3.2
43,478 pl/ha
Co 0.68 0.0 5022 0.0
Cl (Me) 0.67 - 1.5 5141 + 2.4
Cl (M) 0.67 - 1.5 5022 0.0
65,217 pi/he
Co 0.64 0.0 5369 0.0
Cl (Me) 0.60 - 6.2 5706 + 6.3
Cl (M) 0.60 - 6.2 5109 - 4.9
The estimated heritability for grain-to-stover
ratio was 0.16 -+- 0.27, which falls within the
same range as grain yield. This value indicates
that selection for this charac'ter must necessary
show relatively small gains per cycle.
The correlation coefficients are presented
in Table 2A. Highly significant negative', correlations
were found between grain-to-stoVer
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