The phenomenon of in vivo propagation of plantlets from male spikelets in maize-teosinte hybrids was reported earlier by H. K. Singh (MNL56:152, 1983). In our studies, in vivo development of plantlets from tassel spikelets occurred with variable expressivity and penetrance depending upon the parents involved in the crosses. The outer glumes of the spikelets remain normal and the inner glume forms the first leaf. The anther development is suppressed in crosses involving maize and Zea mays ssp. parviglumis, whereas development of anther is normal in maize-Z. diploperennis and maize-Z. luxurians crosses. The plantlets in situ grow into mature plants with height ranging from 40-120cm. The plantlets were generally tripsacoid with female spikelets resembling teosinte. When these plantlets are transplanted at an early stage directly into the field, they grow into normal plants. These transplants (R1) also showed the ability of in vivo regeneration. The R2 progenies also exhibited this phenomenon. The frequency of embryoid formation and subsequent regeneration of plantlets in vivo in the R2 generation was comparable to that of R1 and F1 generations. Analysis of F2 progenies suggests that it is a polygenic trait. Both the cytological and morphological features indicated the sporophytic origin of plantlets.
In vitro culture studies of glumes showed that somatic cells are embryonically determined very early in tassel development. Glumes cultured five days after tassel initiation developed into a whole plant in the medium devoid of hormones. Glumes of F1s cultured in the callusing medium (MS + 2mg/l 2,4-D), showed a high frequency of embryogenic callus which was slightly yellowish, tough with tiny nodules on the surface and contained small oval cells with prominent nuclei and dense cytoplasm (Ann. Bot. 66:497-500, 1990) as compared to the parents. The cross between CM111 and Z. diploperennis produced a very high frequency of embryogenic callus (88.2%) and showed regeneration on hormone free MS medium. This demonstrated that there is endogenous alteration in the auxin-cytokinin balance which is a critical factor for embryo initiation. Occurrence of this phenomenon of in vivo regeneration in maize x teosinte opens up considerable scope for genetic manipulation and helps in studying the regulation of plant development.
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