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 x 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) x 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.