__Inheritance
of kernel‑row number__.

__ __

During the months preceding Dr. Emerson's death he had been engaged in summarizing his work of many years on the inheritance of number of kernel rows in maize. It has been possible, with this material available which included some tabulated data and a partly completed manuscript, to go back through the records and construct a fairly complete picture of the results he had obtained. On the basis of the information collected a paper has been written and is being submitted for publication. The substance of the paper is outlined below.

The original material used consisted of thirteen 12‑rowed,
three 10‑rowed and six 8‑rowed inbreds. Even after many generations
of inbreeding each line continued to show variability for row number, e.g.,
among individuals of the 12‑rowed lines there were characteristically
many with 10 and with 14 rows, and somewhat fewer with 8 and 16 rows on the
ear. The lines were tested for homozygosity of row‑number genes by
demonstrating that selection of ears with diverse row numbers as parents had no
differential effect on the mean row number of their progeny. Similar tests were
conducted on F_{1}'s between inbred lines with the same result; namely,
that selection was ineffective.

The thirteen 12‑rowed genotypes were crossed
in all possible combinations to produce 78 F_{1}'s. Of these 76 had
deviations in the plus direction from the mid‑parent value. The average
increment was +0.85 rows. The six 8‑rowed genotypes were also crossed in
all possible combinations to produce 15 F_{1}'s. Of these 10 had
deviations in the plus direction from the mid‑parent value. The average
increment was +0.09 rows. The 8‑ and 12‑rowed genes were then
intercrossed in all possible combinations (except one) to produce 77 F_{1}'s.
Of these 45 deviated from the mid‑parent value in a minus direction. The
average increment was ‑0.15 rows. The deviations, with the possible
exception of the data on 8‑x8‑rowed crosses, were statistically
significant.

A plausible interpretation of these results was considered
to be: (1)

that the 8‑rowed genotypes contained a
preponderance of dominant genes for decreasing row number, that they differed
from each other by relatively few of these genes and that the slight plus increment
of average F_{1} over mid‑parent value could be accounted for by
general hybrid vigor of the plant; (2) that the 12‑rowed genotypes
contained a more nearly equal number of dominant plus and minus modifiers for
row number and that the greater plus increment of average F_{1} over
mid‑parent value was due primarily to general hybrid vigor (not as
greatly counteracted by a preponderance of dominant minus modifiers as in the 8‑rowed
lines), and (3) that the average minus deviation of the 8‑x12‑rowed
F_{1}'s from the mid‑parent value could be accounted for by a
preponderance of minus modifiers by which the 8- and 12‑rowed genotypes
were presumed to differ (sufficient in number or magnitude of effect to more
than counteract the influence of hybrid vigor).

In order to determine whether the 12‑rowed
phenotypes differed from each other by genes for row number, segregating
progenies (usually F_{3} to F_{5}) from 66 F_{1}'s (all
possible combinations among 12 of the 13 inbreds) were selected for high and
for low row number. Selection was effective in shifting the mean in at least 63
of these progenies. It was concluded, therefore, that 10 of the inbreds each
differed from the other eleven by genes for row number and the remaining two
could be the same as only one other line. This being the case, it should have
been possible to accumulate additional modifiers in either direction by
selection in progeny derived from crosses involving many lines.

Six extracted lines, each derived from crossing four
original 12‑rowed inbreds together, were developed by inbreeding and
selection for a high number of rows for five generations. The means of these
four‑line derivatives were raised above that possible in selections from
crosses between two lines. Finally, three extracted lines of multiple genotype
origin (each derived from intercrosses involving seven of the 12‑rowed
inbreds) were developed by inbreeding and selection for high row number for
five generations. In the F_{5} generation of these three lines the mode
was raised to 22 kernel rows. It has been possible to show, therefore, that by
hybridization among 12‑rowed phenotypes, recombination and selection,
modifying genes for increasing row number were accumulated so that the
expression of this character was raised from 12 to 22 kernel rows on the ear.

H. H. Smith