Cytoplasmic Male Sterility in Helianthus giganteus L. × H. annuus L. Interspecific Hybrids 1

A potential new source of male‐sterile cytoplasm was successfully produced using interspecific hybridization of Helianthus spp. A partial substitution of the nucleus of cultivated sunflower [H. annuus L. (2n 5 34; x = 17)] into the cytoplasm of the perennial H . giganteus L. (2n = 34) was obtained by hybridizing H . giganteus with wild H . annuus , and then backcrossing four times, using the open‐pollinated sunflower ‘Saturn’ as the recurrent pollen parent. Plants with indehiscent anthers and white, rather than normal yellow, pollen were found after two crosses by Saturn. Progeny from these plants were male sterile for two further backcrosses. In vivo germination tests of pollen from 20 such male‐sterile plants indicated complete pollen sterility for 15, but normal seed set when cross‐pollinated, suggesting that female fertility was not affected. Crosses between an inbred tester line without genes for pollen fertility restoration as the pollen parent and an existing source of male‐sterile cytoplasm or four putative malesterile backcross lines as the female parents, failed to restore pollen shed in the 15 F 1 families evaluated. In similar crosses using three pollen fertility restorer sources as the pollen parents, pollen shed was restored in some or all plants of nine F 1 families involving an existing source of male‐sterile cytoplasm. However, pollen shed was restored in male‐sterile backcross lines by only one of the three pollen restorer sources, suggesting that the backcross substitution lines from H . giganteus are a potential new source of male‐sterile cytoplasm, which has been designated as cms 3 .