There are many factors that influence maize callus growth in vitro, including genotype, source and stage of donor tissue and medium components. In previous investigations (Rapela, MNL 58:110-112, 1984) we have detected differences in the percentage of formation of compact callus tissue and of such callus forming somatic embryos due to the genotype and the effect of the medium. New results in our laboratory reveal that genotype (inbred or hybrid nature of the explant) is not an important factor in determining the response for somatic embryogenesis in vitro. Also, differences between media basal components did not have as much influence on somatic embryogenesis as did the amount of sucrose and proline.
The stage of donor tissue, however, seems to be a very important factor in obtaining somatic embryogenesis in vitro. We investigated the relationship between developmental stage of the embryo at the time of excision and the percentage of formation of organogenic or embryogenic tissue (Table 1).
Younger embryos, less than 0.9 mm in length, showed poor or no response in Medium B and Medium C. In Medium A, the percentage of such embryos forming organogenic callus was reduced. Older embryos, larger than 3.5 mm in length, showed no response and germinated in Medium B and Medium C. Attempts to induce formation of embryogenic tissue from mature excised embryos were done with several genotypes using different 2,4-D concentrations and with or without agar, but we have not obtained any positive results.
These results with floury-a, flint and fl-a x flint hybrid genotypes are consistent with the results obtained by Lu et al. (TAG 66:285-289, 1983) working with dent genotypes. On the other hand, the induction of soft and friable (organogenic) callus in Medium A appears, to a great extent, independent of the developmental stage of the donor tissue.
Table 1. For references see above. Between 10 and 15 embryos were cultured in each medium.
Miguel Angel Rapela
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