Sunflower Interspecific Hybrids and Amphiploids of Helianthus Annuus ✕ H. Bolanderi

Abstract

Sterility in F1 sunflower (Helianthus annuus L.) interspecific hybrids limits utilization of wild Helianthus species for the improvement of cultivated sunflower. This experiment was conducted to simplify and improve the effectiveness of the colchicine chromosome doubling technique, to analyze the resultant tetraploids, and to evaluate the role of chromosome doubled sectors of H. annuus ✕ H. bolanderi Gray F1 hybrids in improving backcross seed set. Apical meristems of seedlings were submerged in 150 or 250 mg L−1 colchicine solutions with 0.02 L L−1 dimethyl sulfoxide (DMSO), at pH = 5.4 for 5 h in the dark. Frequency of amphliploids, meiotic chromosome pairing, pollen stainability, and seed set were determined. The 150 mg L−1 colchicine treatment resulted in doubled sectors in 32% of the P21 ✕ H. bolanderi hybrids. Tetraploids had larger disk florets and pollen grains. Gross morphology of the tetraploid plants was similar to their diploid progenitors. Diploid P21 ✕ H. bolanderi hybrids had 5 to 6% pollen stainability and set an average of 4.5 seeds per head upon sib‐pollination. Multivalents at diakinesis involved as many as 14 chromosomes and indicated that P21 and H. bolanderi differ by seven reciprocal translocations. Chromosome doubling increased sib‐pollinated seed set to 61.8 seeds per head. Backcrosses of the amphiploids with P21 and inbred line HA89 set 13.3 and 3.0 seeds per head, respectively. Pollinating P21 and HA89 with pollen from the amphiploid resulted in 45.8 and 38.8 seeds per head, respectively. This seedling colchicine treatment was effective for doubling the chromosomes of the P21 ✕ H. bolanderi hybrids, and the resultant amphiploids had improved fertility and sufficient backcrossed seed set for efficient gene transfer into cultivated sunflower.