Influence of picloram and thidiazuron on high frequency plant regeneration in elite cultivars of wheat with long-term retention of morphogenecity using meristematic shoot segments

Meristematic shoot segments (MSSs) were used to develop an efficient and reproducible regeneration system via multiple shoot differentiation in two elite cultivars of winter wheat. Cylindrical basal shoot segments, 3-4 mm in length, were excised from seedlings derived from mature embryos that had been germinated directly on MS-based medium containing growth regulators. These segments were further cultured on the same medium formulations. Out of 24 variations analysed, the combination of 2 mg/l 4-amino-3,5,6-trichloropicolinic acid (picloram) + 3 mg/l thidiazuron (TDZ) was found to be the most effective in inducing clumps of multiple shoots/buds with little callusing. Sectors of these clumps were (1) further multiplied by biweekly subculturing on 2 mg/l picloram + 2.5 mg/l TDZ leading to highly differentiating green clusters of buds without loss of morphogenesis for more than 12 months so far, and without albinism, or (2) transferred to 0.1 mg/l picloram + 1 mg/l TDZ for shoot development and elongation. The elongated shoots rooted on basal medium with 0.5 mg/l indole-3-butyric acid (IBA) were transferred to soil and showed normal growth and fertility. Both cultivars formed multiple shoots ranging from 28 to 33 per responding MSS after 10-12 weeks.