Hayes and Garber - Cucurbit Breeding

184 BREEDING CROP PLANTS
Xenia may result from crossing varieties which differ in a
single visible endosperm character. When a character difference
is dependent on a single dominant factor, xenia occurs only when
the factor is carried by the male parent, or, when dominance is
incomplete, xenia results when either variety is the male. When
a character difference is dependent on more than one factor, all
located in one parent, and dominance appears complete, xenia
occurs only when these differential factors are located in the
male; when dominance is incomplete, xenia occurs if the factors
are located in either parent. When two varieties have a similar
character or a different character expression but contain between
them endosperm factors necessary for the production of a new
character, xenia occurs when either variety is the male.
The inheritance of an intermediate starchy-sweet (called
pseudo-starchy) condition, which is often present in some sweet
corn ears, has been studied by Jones (1919). Three factors were
shown to explain the results: (1) a plant factor, A, necessary for
complete expression of the so-called pseudo-starchy character;
(2) an endosperm factor, B, which prevents the characteristic
shrinking of sweet seeds ; (3) an endosperm factor, C, determining
C gives complete dominance, while A and B give an
opaqueness.
intermediate condition when heterozygous, and B in addition
shows a cumulative effect in proportion to the number of factors
involved. C and c give the greatest differential effect only
in the presence of the homozygous condition for A and B. From
this brief discussion it is easy to see that reciprocal crosses
between AABBcc X aabbCC will not give like results. AABBcc
fertilized with aabbCC will give an endosperm condition ABBbcC,
while the reciprocal cross will give abbBCc. As A is necessary
for recognizable expression of pseudo-starchiness, one cross
will show xenia while its reciprocal will not.
The following endosperm characters have been studied and
the results are briefly summarized. (See Table XXXIX.)
The cross between the waxy variety of Chinese maize and
American sweet varieties is of interest, as in FI maize with a
corneous endosperm was obtained, while in F^ a ratio of 9
horny to 4 sweet to 3 waxy seeds was obtained. Many starchysweet
crosses have been studied and as yet no case has been
obtained which showed more than a single main factor difference.
Apparently the sub-species, Z. mays saccharata, differs by only
a single main factor from the starchy subspecies.