Interspecific hybrids between helianthus PetiolarisNutt. and H. Annuus L.: Effect of backcrossing on meiosis

Abstract

Interspecific substitutions of the nucleus of Helianthus annuus (2n=34) into the cytoplasm of H. petiolaris (2n=34) were obtained by successive backcrossing using cultivated sunflower, H. annuus, as the recurrent pollen parent. Meiosis in the F1 was characterized by multivalents, suggesting that 10 of the 34 chromosomes were heterozygous for chromosomal interchanges. An additional pair of chromosomes also contained a paracentric inversion. Continued backcrossing resulted in rapid elimination of the meiotic aberrations evident in the F1. In the BC1, 1 of 11 plants had normal meiosis and by the BC2, only 13 of 54 plants had meiotic aberrations similar to those of the F1. However, trisomic progeny (2n=35) were found in 3 of the 11 BC1 plants and 20 of the 54 BC2 plants. No meiotic aberrations were observed in BC3 or BC4 plants. Plants with indehiscent anthers, and considered to be male sterile (M.S.), first occurred in the BC1 and, by the BC2, 51 of 54 plants were M.S. All 19 BC3 and 16 BC4 plants were M.S. Preliminary investigations suggest that the pollen from such plants is sterile and that the sterility is cytoplasmic rather than genetic. Disc-flower measurements were a useful technique for selecting samples at the correct stage of microsporogenesis, but could not be used to distinguish between successive backcrosses.