Doubled haploid (DH) system is an effective tool in improving breeding efficiency and has been widely applied in wheat breeding programs. Wheat x maize hybridization is used for the production of wheat DH because of its efficiency and ease of application. We carried out an experiment to investigate genotype effect of wheat (Triticum aestivum) and maize (Zea mays) on efficiency of wheat haploid production. In various wheat x maize crosses, ten wheat and seven maize genotypes were tested. Haploid embryos were rescued and cultured for plant regeneration. Average seed set, embryo formation and haploid regeneration of five wheat varieties in crosses with a pollinator cv. Gangdaok were about 75%, 19% and 8.4%, respectively. Their haploid regeneration ranged from 3.7~9.8% and cv. Jokyoung showed highest regeneration. Average seed set, embryo formation and haploid regeneration of seven maize genotypes in crosses with a parent cv. Jokyoung were about 78%, 18% and 9.6%, respectively. Their haploid regeneration ranged from 7.6~12.9% and cv. Kwangpyeongok showed highest regeneration followed by cvs. Gangdaok and Gangilok. Analysis of variance for seed set and embryo formation showed highly significant effects of wheat parents and maize pollinators, whereas their interaction effect was only significant for seed set. The effect of maize genotypes on these traits was greater than that of wheat genotypes. Consequently, cvs. Kwangpyeongok, Gangdaok and Gangilok were found to be better pollen donors among the genotypes tested in wheat x maize hybridization for wheat hybrid production.

This study was conducted to isolate a salt tolerant gene and to develop salt tolerant rice for reclaimed-saline areas through genetic transformation. A rice c/DRE binding factor 4 (OsCBF4) cDNA was isolated from rice (cv. Nipponbare) using RT-PCR. The full-length cDNA of the CBF4 gene consists of 1,429 nucleotides and 274 amino acid residues. The OsCBF4 shares from 33 to 49% identity of deduced amino acid sequence with other CBFs of rice. In order to develop salt tolerant rice, transgenic rice plants containing the OsCBF4 gene were obtained via Agrobacterium-mediated transformation. The stable incorporation of the OsCBF4 gene into rice genome was confirmed by PCR and Southern analysis. The stable expression of introduced gene was also validated by RT-PCR analysis in T₂ plants. Biological assay of T₃ progeny of the transgenic plants in Yoshida solution containing 120 mM Nacl for 2 weeks, confirmed that the OsCBF4 confers salt tolerance to transgenic rice plants. OsCBF4 transgene in the transgenic line CBF4-10 was markedly expressed up to over three-fold in the leaf by 120 mM NaCl treatment. Real-time PCR analysis revealed that the levels of the transgene expression were markedly increased under salt treatment. The transgenic line CBF4-10 which showed highest ability to recover from the saline stress could be used as a potential source for salt tolerance in rice breeding programs.