Inheritance of earliness in certain varieties of spring wheat

1. Results are reported on the inheritance of earliness in various crosses between six varieties of spring wheat. 2. The date when the tip of the first head of each plant emerged from the top of the sheath was used as the index of earliness. 3. Parents, the F1, and the F2 generations were planted the same day and grown for comparison in 1925. In 1926 a similar comparison was made between the parents, the F2, and the F3 generations. 4. The mean of the F1 population was intermediate but nearer to the early parent than to the later parent. The means of the F2's were intermediate or tended toward the early parent. 5. The F2 was more variable than either parent and extended over a range approximating the combined range of both parents. The F3 families showed almost all degrees of earliness within the limits of the parent varieties. In one cross neither extreme was reached, in another the extreme of the late parent only was reached, while in a third the extremes of both parents were exceeded. 6. The data indicate that earliness may be due to the action of a number of independent multiple factors having cumulative effect. From the evidence available, however, it is impossible to draw definite conclusions as to the exact number or value of the factors concerned. 7. Where the parental types are not recovered in F2, it is probably due to insufficient numbers. Where the parental types are exceeded, there is evidently a case of transgressive inheritance. 8. In the cross between Federation and Master a positive correlation was found between number of days from planting to heading and the height of plant, the correlation coefficient being 0.394 +/- .019. 9. The occurrence of dwarfs in the cross between Federation and Master is discussed. It is explained by assuming the interaction of two pairs of factors, "D", a dominant factor for dwarfness, and "I", an inhibitor, which, when present in the dominant form, prevents the appearance of the dwarf character.