The effects of level of 2,4-D and time in culture on regeneration rate and chromosome numbers of regenerants from calli of the hybrid Triticum aestivum cv. Chinese Spring ph1b × Thinopyrum ponticum (2n = 10x = 70)

Thinopyrum ponticum (Podp.) Barkworth &D. R. Dewey (2n = 10x = 70) has excellent resistance for both leaf and stem rusts. Long-term callus cultures were established from the immature embryos of a hybrid between Triticum aestivum L. (2n = 6x = 42) × Th. ponticum. They were maintained in culture for over 2 years and continued to grow and have organogenetic capacity. With increasing time on a maintenance medium, the plant regeneration rates of the hybrid calli decreased when transferred to regeneration media containing 0.1, 0.2, or 0.5 mg/L 2,4-D, but the rate of decrease was much higher at 0.5 mg/L than at either 0.1 or 0.2 mg/L 2,4-D. After 3 months of subculture, the highest plant regeneration rate was obtained on the medium containing 0.5 mg/L 2,4-D (1.11 plantlets/callus), while on the 24th month of subculture the highest plant regeneration rate was obtained on the medium containing 0.1 mg/L 2,4-D (0.20 plantlets/callus). Thus, it was shown that as the calli aged it was important to reduce the level of 2,4-D in the regeneration medium. Over 2 years, a total of 667 regenerants were successfully transferred and grown to maturity. Chromosome numbers in root-tip cells were determined for 539 regenerants and ranged from 36 to 70. Telocentric chromosomes were frequent. A fertile plant was found among the regenerants after 15 months of subculture. It had 56 chromosomes with 2.15 (1–6) univalents, 22.76 (17–26) closed bivalents, 3.55 (1–9) open bivalents, and 0.41 (0–3) trivalents and was highly resistant to stem rust race 15B-1. Callus culture of wide hybrids can be used to introgress characters from alien species into wheat.Key words: wheat, callus culture, long-term regeneration, wide hybridization.