1. Male sterility.
Plantings of various white single, 3‑way and double crosses continued the past two years showed a number of additional inbred lines as carrying the necessary factors to cause pollen sterility when used as the male parent on 33‑16 or Ky 27. No white inbreds other than 33‑16, Ky 27 and Mo 2RF were found to carry the cytoplasmic contributions for sterility except 33‑16 made waxy. The yellow single cross M 1984 x M14, supplied by Dr. G. F. Sprague, was 100 per cent incompletely sterile whereas the reciprocal was normal. Five cytoplasmic male sterile yellow crosses supplied by Dr. D. F. Jones ranged from 40 to 100 per cent completely sterile.
Poor seed set has occurred in commercial hybrids which have exhibited only 20 per cent male sterile plants when it would seem the remaining plants should furnish sufficient pollen to produce good set. By keeping tassels bagged throughout the pollen shedding period and measuring the amounts of pollen produced it was found that pollen shedding plants in male‑sterile hybrids produced only 67 per cent as much pollen as plants in non‑sterile reciprocals.
Crosses made using 33‑16 as the seed parent and backcrossing to 33‑16 three times continued to exhibit male sterility, whereas when 33‑16 was used as the pollen parent in making the original cross and backcrossing to 33‑16 three times the plants have been normal, showing that 33‑16 carries a cytoplasmic contribution for sterility.
L. M. Josephson