Coleoptile Length of Dwarf Wheat Isolines

The dwarfing alleles in wheat (Triticum aestivum L.) are associated with shorter coleoptile length that can produce unacceptable and erratic stands. The combined effect of temperature (2, 10, 18°C) and five gibberellic acid (GA) concentrations [0, 5, 50, 100, 500 mg L−1 of potassium gibberellin A3 (C19H21O6K)] in the germination medium on the coleoptile length of four homozygous isolines [normal or T‐0 (Rht‐B1a/Rht‐D1a), semidwarf‐1 or SD‐1 (Rht‐B1b/Rht‐D1a), semidwarf‐2 or SD‐2 (Rht‐B1a/Rht‐D1b), dwarf or D‐12 (Rht‐B1b/Rht‐D1b)] in ‘Marfed’ (spring) and ‘Burt’ (winter) was studied. With each decrease in temperature, the coleoptile length in each isoline and cultivar increased, with the increase greater in those isolines and cultivars having the shortest length at 18°C and containing at least one dwarfing allele (Rht‐B1b and/or Rht‐D1b). At 2°C, higher GA concentrations increased coleoptile length over 0 GA mg L−1 in all isolines, with the greatest increase at the 500 mg L−1 concentration. The three midconcentrations (5, 50, 100 mg L−1) resulted in an intermediate but almost equal increase. Increasing temperatures decreased the response to GA so that at 18°C, only T‐0 and SD‐1 responded to GA applications. The reported “GA insensitivity” was found to be highly temperature dependent, with the Rht‐B1b allele having a wider temperature response range than Rht‐D1b The results suggested that differences in genetic background, possibly related to the winter–spring growth habit, could influence the effect of the dwarfing alleles.