Interspecific substitutions of the nucleus of Helianthus annuus (2n = 34) cv. Saturn into the cytoplasm of H. petiolaris (2n = 34) by successive backcrossing, resulted in progenies with indehiscent anthers contaimng white, rather than normal yellow, pollen. Further backcrossing by cv. Saturn failed to restore pollen shed, suggesting that the male sterility was cytoplasmic. In vivo germination tests of pollen from 23 such plants from eight BC, lines, indicated complete pollen sterility for 14 plants, but normal seed set, suggesting that female fertility was not affected. Meiosis in all plants examined was normal.
Crosses between seven sources of pollen-fertility restorer, one collection of wild H. ~N~UUS, and an existing source of cytoplasmic male sterility, resulted in a high frequency of plants with normal pollen shed in all F, progenies. However, no normal pollen shed was evident in F, progenies for similar crosses between BC, male-steriles and three of the seven restorer sources, nor for the single wild H. annuus evaluated. The foregoing suggests that the backcross substitution lines are a new source of cytoplasmic male sterility. The inheritance of restoration of pollen shed was complex and not fully elucidated. Some data suggested that two independent, complementary, dominant genes were required, but others indicated two to three independent, dominant genes.