Seedlings of the Helianthus annuus inbred lines P21 and HA89 were treated with colchicine to study chromosome doubling. Frequency of tetraploids, meiotic chromosome pairing, pollen stainability, and fertility were examined. Five-hour colchicines treatments at 0.15%, pH 5.4, with 2% dimethyl sulfoxide resulted in tetraploid sectors on 42% of P21 and 11% of HA89 plants. Tetraploids had larger disk florets and larger pollen grains. Otherwise, tetraploid plants were morphologically similar to their diploid progenitors. Tetraploidy in P21 was not stable, with plants having 2n = 4x = 65 to 70 chromosomes. Tetraploid plants of HA89 had reduced vigor and did not produce seed. At diakinesis, tetraploid P21 plants had an average of 0.85 univalents, 21.12 open bivalents, 6.66 closed bivalents, 0.21 trivalents, and 2.74 quadrivalents per cell. The number of chiasma per chromosome pair in P21 was reduced from 1.50 for diploid to 1.32 for tetraploid plants. Pollen stainability in tetraploid P21 was less than 50% and the plants produced an average of eight seeds per sibbed head, about 1% of normal seed set. Reciprocal crosses of diploid and tetraploid P21 produced four triploid plants. Backcrossing triploids to P21 produced 137 plants with 2n = 34 to 47 + t. Thirty-one of these plants were trisomies having 2n = 35.Key words: Helianthus annuus, tetraploids, triploids, trisomies.
Self- and cross-pollination effects on pollen tube growth and seed set in holm oak Quercus ilex L (Fagaceae)
