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A project was initiated in 1968 to evaluate
the value of mass selection for prolificacy as
a means of population improvement in tropical
germ plasm grown under local conditions. A
second objective was to determine if a genotype
x plant density interaction could be detected
in the original and selected populations.
Three sources of germplasm were chosen,
one being somewhat prolific (Va- Cuba 11J x
Georgia cow corn) and two non-prolific (V 1 ­
Cuba 11J x V 2 -Ooeto and Veracruz 181 x Antigua
Gr. 1). Two cycles of selection were
carried out in both 1968 and 1969. Plantings
of 26,000 plants per hectare were made and
individual plants with strong prolific tendency
at flowering were selected. Pollen from selected
plants was bulked and used to pollinate
most plants in the block.
At maturity, prolific plants were harvested
and seed bulked to form the next cycle. About
1000 plants were used each cycle, from which
10 to 12 percent were selected for the next
cycle.
In 1969, the four cycles of selection were
compared with the original varieties for earnumber
and grain yield at a plant density of
40,000 plants/ha. The last cycles (P/ 4) were
also compared with the original varieties (P/ 0)
at three plant densities (26,000; 40,000 and
53,000 plants/ha.
The findings suggest that selection resulted
in a small increase in ear number, but was
ineffective in altering grain yield. There were
changes in both grain yields and ear number
due to selection, although the former character
was not consistent in its performance over
varieties or densities. However, there were
no significant first-order interactions in the
second irial.
Results from the 1969 evaluation tests suggest
that the prolific character did not respond
rapidly to selection. These results were
not expected, as previous reports had indicated
relatively high heritability for this trait.
Even though ear number was increased, the
magnitude of the response was not encouraging
on a per-cycle basis. At best, the average
increase over all varieties was only 3.5 percent
per cycle for ear number and 2.3 percent per
cycle for yield. Results are not conclusive that
yield was Improved by selection for increased
ear number.
Several factors may be involved in the lack
of rapid response to selection based on the
prolific character. Further tests should reveal
if the present results are valid. If the 1969
tests do represent a true evaluation of selection
progress, other factors must be considered.
One or more of the following could be
important factors in selection response: (1) A
season x genotype interaction may exist that
reduces effectiveness of selection in an "offseason".
(2) Selection procedures wete such
that true prolific plants were not identified at
pollination. (3) The character, ears per plant,
is not as highly heritable as suggested in
other studies.
Maturity and Yield Relationships
Another study was initiated in 1968 to investigate
the relationship of maturity and yield
within three genetic popUlations. The procedure
was designed to separate each variety
into early, medium, and late-maturing groups
by a modified mass selection scheme.
Significant changes in maturity occurred in
both directions as a result of selection, when
maturity is measured by silking date. Similar
changes were noted in moisture content at
harvest. The average changes were rather
small for early maturity (1.3 days per cycle)
and for late maturity (approx. 1 day per cycle).
However, this was expected under such mild
selection intensity. The greatest change was
shown by Antigua 20 x Okuzuruwase (population
1), for earliness. This change was
probably related to more vigorous selection in
the first cycle.
Grain yields tended to be maintained in the
early groups, but increased in two populations
for the medium and late groups. However,
rigid selection for grain yield per se, was not
practiced. Plant height was positively related
to maturity. The strongest association was
observed in the Antigua 20 x Okuzuruwase
variety, where 15 and 9 centimeter height
differences were recorded between early-medium
and medium-late maturing groups, respectively.
Results of this experiment suggest the possibility
of maintaining, or even increasing, the
grain yield of the source population, with
rather mild selection for earliness. The study
may suggest that this procedure, when carried
out on a larger scale, could be effective in
producting high yielding, early-maturing varieties.
Soil Fertility Experiments
Two experiments were conducted at Farm
Suwan in 1969 in an attempt to establish response
curves of maize varieties to changes
in soil fertility. The first experiment was de-
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