1. In the second generation from crosses of deviating lines with the original normal line, mono-factorial segregation is indicated by dwarf plant, pale top and crooked stalk. (Backcrossed ratio 52 tall; 32 dwarf where 42:42 were expected. F2 selfed 49 green straight, 9 green crooked, 23 pale straight, 3 pale crooked where 47:15:15:5 were expected.) Narrow leaf cannot be separated clearly from normal in individual plants. F3 progenies ranged in average leaf width from 74 to 93 mm compared to 72 for narrow and 92 for normal under similar conditions. Average height ranged from 92 to 103 inches compared with 91 for narrow and 95 for normal. In previous tests narrow leaf plants have been slightly taller than normal. Both the extracted homozygous normals and deviates have come out of the cross slightly enlarged, an indication that other factors are involved. Further testing is necessary to establish the significance of these differences.
Blotched leaf and late-flowering types have not yet been compared after extraction from the cross with normal.
In view of the fact that the long inbred Leaming lines continued to decline in yield during 20 generations it is quite possible that these lines which have not been selfed continuously for this length of time are still segregating for minor physiological changes along with the visible morphological changes which seem to be mutations.
The normal lines, in the two cases tested, show no increases when crossed with the same normal lines from which they have been separate for many generations. Therefore, the possibility of accumulation of dominant genes from both parents seems to be ruled out. Further testing of this point is needed.
There is the possibility of mutations or delayed segregations affecting combining ability that have no visible effect in the homozygous condition or in crosses with the same line from other sources. Three of the long inbred Leaming lines selfed for eight and nine generations were separated into two sub lines each and maintained separately for seven additional generations of self-fertilization. During this period they showed no visible differences but when intercrossed they all gave significant increases in some measurable character.
Two of these lines were again separated in the 17th and 22nd generations and further self-fertilized for eleven and six generations. When the first generation crosses between these sub lines were compared with their normal parents no significant differences were obtained. In one of these cases the parental lines differed slightly in visible characters. All of this evidence indicates delayed segregation from an enforced heterozygous complex.
Five of the six deviating lines which show heterosis when crossed back to the normal line have been tested in outcrosses with unrelated lines. No significant differences in yield of grain were obtained between crosses of normal by unrelated normal compared to deviating line by the same unrelated normal. For practical purposes it is important that there were no decreases in yield.
D. F. Jones