Effects of various phytohormones on haploid wheat production in wheat x maize crosses

The effects of phytohormones on the production of haploid wheat were examined in the intergeneric crosses between Japanese wheat cultivar (Triticum aestivum cv. Zenkojikomugi) and maize (Zea mays cv. Pioneer P80 Lisa). The detached wheat spikes pollinated with maize were cultured in a solution containing sucrose and sulfurous acid supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D), indole-acetic acid, naphthalene acetic acid, kinetin or 6-benzylaminopurine at 0, 0.1, 1, 10, 100 or 1000 mg L-1. Haploid embryos obtained were cultured on agarose-solidified B5 medium. The frequency of plant regeneration was significantly affected only by the treatment with 100 mg L-1 2,4-D. Thus, the detached spikes were cultured in the medium containing 2,4-D at 0, 25, 50, 75, 100, 125, 150, 175, 200 or 400 mg L-1. The treatments with 50 mg L-1 2,4-D increased the embryo size, but the treatments with above 75 mg L-1 2,4-D inhibited the development of the embryo. The percentage of florets developing into haploid plants was increased by the treatment with 100 mg L-1 2,4-D. Therefore, the concentration of 2,4-D in the spikes treated with 2,4-D at 50, 100 and 150 mg L-(1) were measured by gas chromatography. The concentration of 2,4-D in the seed was increased to 9.24 ppm by the treatment with 100 mg L-1 2,4-D, a further increase of 2,4-D concentration in the medium having no effect. On the other hand, the concentration of 2,4-D in the glumes and rachis increased up to 12.72 and 41.55 ppm by the treatment with 100 and 150 mg L-1 2,4-D, respectively. The treatments with 2,4-D at a concentration higher than 100 mg L-1 inhibited embryo development. The present results suggested that 2,4-D at the concentrations from 50 to 100 mg L-1 would be optimum for haploid wheat production using maize.