In order to study the genotype, age-size and hormonal dependence on callus initiation and maintenance, several tissue cultures of maize were carried out utilizing immature embryos of a floury-a x normal red flint hybrid, its parent inbred lines and other floury-a inbred lines. The culture protocols were the same as Green and Phillips (Crop Sci. 15:417-421, 1975), except that cultures were maintained in the dark at 28 C.
Figure 1 shows what apparently would be an optimal embryo age-size, in which the hormonal requirements would be the lowest for a good callus growth. Although the parameter used is not strictly the same, this result is in part different from Green's (Hortsci. 12:131-134, 1977), since he found a decrease of the percent of regenerating scutellar callus with embryo age.
Figure 2 shows the influence of genotype and 2,4-D concentration on the growth of callus. These results are in agreement with Green's, in the sense that immature embryos derived from hybrids produced callus at frequencies much higher than embryos from either parent individually.
Figure 3 shows the influence of genotype and orientation of maize embryos on the growth of callus. These results are also in agreement with the observations of Green and Phillips, but different from the ones of Harms et al. (Z. Pflanzenzucht. 77:347-351, 1976). When the orientation of the scutellar side was upwards, all of our primary cultures exhibited a short coleoptile emergent from the proliferating callus tissue. The subsequent embryo growth was quickly suppressed and the callus growth was fast. However, when the orientation of the scutellar side was downwards, the cultures exhibited long coleoptiles from the plumule-radicle axis, and very poor callus formation.
These preliminary results suggest that callus cultures (perhaps differentiating) can be obtained from immature floury-a and +/floury-a embryos. However, there is variability between genotypes in capability to initiate callus cultures. Hence, the optimal embryo age-size for excision and the hormonal requirement should be
tested for each particular genotype.
Miguel Angel Rapela
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