"Scattergrain" white double crosses.
In the fall of 1945 a number of farmers' fields of hybrid corn were reported in Kentucky, Tennessee and Indiana which failed to set seed properly. In several fields examined near Henderson, Kentucky, the seed set ranged from as low as about 20 per cent to 85 per cent or better. The difficulty received considerable local publicity and the hybrids concerned were locally designated as "scattergrain" hybrids. The trouble was restricted to white hybrids but the reports indicated that hybrids from several different seed corn companies were involved. Evidence pointed to male sterility on a field‑wide scale as the cause of the poor seed set. The amount of sterility occurring in the same hybrid varied from field to field and seemed to be worse in bottom‑land fields that were planted late.
On the basis of information obtained on the pedigrees of sme of the offending hybrids, seed of a series of reciprocal single crosses was collected or produced in the greenhouse during the winter of 1945‑'46. Observational plantings of these singles and several of the "scattergrain" double crosses were made at Lexington, Berea and Henderson, Kentucky, and at Beltsville, Maryland, in 1946. The data obtained do not permit a critical analysis of the cause of the sterility as, for some unexplained reason, the sterility occurred with a much lower frequency in the single crosses than in the double crosses. Sufficient data were obtained on the sterility, however, to suggest the following as important contributory factors:
1. The sterility seems to occur only in crosses which have a cytoplasmic contribution from 33‑16, an old inbred line developed in Indiana.
2. Sterility in the hybrids also is influenced by contributions from the male parent. The substitution of only one line in the male parentage of one of the "scattergrain" double crosses, completely eliminated the sterility in the resulting double cross.
3. The expression of the sterility is very subject to environmental influence.
Merle T. Jenkins
L. M. Josephson