To improve haploid plant production in durum wheat, the haplomethod involving intergeneric crossing with maize followed by embryo rescue was used. The influence of parental genotypes and various experimental factors were studied. Ten cultivars of Triticum turgidum ssp. durum (female parent) were crossed with eight genotypes of Zea mays. After pollination, plant stems were either maintained in situ or cut near the base and kept in a 2,4‐dichlorophenoxyacetic acid (2,4‐D)‐sucrose solution. Ten to 18 days after pollination, embryos were excised from developed ovaries and cultured on one of MS, MS/2, or B5 media. Haploid embryos and plants were obtained (78 green haploid plants regenerated in 0 year). The wheat genotype was significant for ovary development, embryo and plant formation, whereas the maize genotype was significant only for embryo formation. Detailed results of all crosses showed the best crossing partner for each wheat genotype. Cutting the plant stems after pollination gave better results than maintaining them in situ. The optimal stage for embryo rescue was 14 days and B5 and MS/2 media were more efficient than MS for embryo culture.
Small explants composed of 3-6 layers of epidermal and subepidermal cells excised from floral branches of Nicotiana tabacum are capable of de novo organogenesis. Continuous mitoses without organogenesis, or mitoses followed by the formation of floral buds, vegetative buds or roots can be obtained by varying the auxin-cytokinin-sucrose ratio in the medium. The physiological stage of the floral branches, and light and darkness had also an influence on the de novo organogenesis. Best floral-bud formation was obtained when explants were taken from plants in which the terminal bud was in the green-fruit stage, and were cultured on a medium with indole-3-acetic acid and kinetin both at 10(-6) M and with 3% sucrose, in the light. For differentiation of vegetative buds, the optimal auxin/cytokinin ratio was one tenth of that for floral-bud formation, while the sucrose concentration was the same. Optimal conditions for root formation were: explants from plants in which the terminal bud carried a mature fruit; 10(-7) M kinetin, 10(-5) M indole-3-butyric acid, and 1% sucrose in the medium; and culture in darkness. The optimal medium for callus formation contained 5×10(-6)M 2,4-dichlorophenoxyacetic acid, 10(-7) M kinetin and 3% sucrose.
Thin explants composed of the epidermis and underlying coUenchyma excised from leaf veins of Begonia rex and cultured in vitro are capable of neoformation of unicellular hairs, roots and buds. Unicellular hairs were formed over the entire surface of the explant when 10-^ M indole acetic acid or 10-'' M naphthaleneacetic acid (NAA) was added to the basal medium; each epidermal cell was potentially involved. The epidermis was most sensitive to a NAA treatment during the first few days of culture but 30% of the explants could still react after 4 days of culture without NAA. When NAA (5 x 10-'' M) and a cytokinin, zeatin (10-^ M), were added together, roots were formed from epidermal tissue after numerous divisions in the original cells. Their initiation was not related to particular cells. Buds were formed when a cytokinin (10-*' M) was added to the basal medium; bud meristems were formed from small groups of cells surrounding basal cells of glandular hairs. Hair formalion was inhibited by either high (32-27°C) or low (12°C) temperatures applied continuously. 32-27 C seemed to inhibit elongation of the hairs specifically, whereas 12 C inhibited earlier phases in hair formation. This hypothesis was supported by short temperature treatments applied at different times during hair formation.
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