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With the same purpose in mind, 35 Sl
lines derived from combinations of USA Corn
Belt and Mexican germplasm were used to
generate the same two types of population
with respect to leaf orientation. These populations
went through one cycle of synthesis
at EI Roque, Guanajuato, Mexico in 1969.
The process of developing several lines
differing in leaf orientation is underway on 47
S~ lines of Tuxpeno.
Defoliation trials: A number of defoliation
trials have been carried out involving the following
treatments: (1) control, (2) removal of
leaves above the ear, (3) removal of leaves
below the ear, (4) removal of alternate leaves,
(5) splitting and remova~ of one-half of the
leaf blade on all leaves, (6) tying-up of leaves
above the ear to an angle of approximately
10°, (7) same as No. 5 above, plus tying up
of leaves above the ear to an angle of 10°,
(8) splitting and removal of one-half of the
leaf blade above the ear and tying up of
leaves above the ear.
The experimental findings indicate a trend
toward a decreased per-plant grain yield due
to removal of leaves above the ear. This decrease
seems to be equal to, or greater than,
the decrease due to removal of the leaves
below the ear.
The effect on grain-per-plant, due to tying
up the leaves above the ear to a more erect
position, is not clear. However, there are
some indications of a beneficial effect of erect
leaves at high population densities (higher leaf
area indices). In treatments where one-halt
of each leaf was removed along the midrib,
a detrimental effect was observed when the
leaves above the ear were tied in the erect
position.
Two plants from the same population (Tuxpefio
brachytic-2) exhibiting marked differences in leaf
habit (or angle). By breeding for. erect leaves it
is hoped to improve light interception particularly
at high population densities.
Maximum Yield Study
A study was initiated at Tlaltizapan in
June, 1969, to investigate the yields obtained
on a per-unit-time and per-unit-Iand area basis.
High popUlations and continuous cropping
were used. Initially, the varieties chosen for
this experiment were two improved populations
(Caribbean Composite and Tuxpeno Composite)
and two unimproved collections (Guerrero
221 of the race Pepitilla, and Oaxaca 179,
of the race Zapalote Chico). The Zapalote
Chico is very early, and short in stature, while
the other three varieties are late and tall. Each
variety was planted at three popUlations densities
and fertilizer was applied at the same
rate on a per-plant basis in all densities.
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