Corn shoot cultures would be useful for micro-propagation of exceptional genotypes, haploids, etc., and for continuously supplying homogeneous, sterile leaf material for mesophyll protoplast isolation. There was no report up to now of in vitro shoot cultures of corn. The majority of corn lines in normal use possess little or no tillering capacity. Field grown plants of a teosinte collection, El Salado, gave numerous tillers and many axillary branches. Scutellum cultures from immature embryos of B73 x El Salado were induced. These cultures regenerated numerous plantlets during subsequent passages. The plantlets, when transferred to MS medium containing sucrose (30 mg/l), IAA (2 mg/l), kinetin (2 mg/l) and agar (0.8%) gave continuous shoot proliferation. The cultures were incubated at 27 C under 16 h photoperiod at 5000 lux. Shoots from mature seeds of B73, El Salado, and B73 x El Salado were also tested for in vitro shoot culture capacity using similar culture conditions. B73 showed absolutely no response while El Salado and hybrid shoots gave similar results as those of plantlets from immature hybrid embryo cultures. In corn the ability to give in vitro shoot cultures appears to correlate with tillering capacity at the plant level, and may be a further indication (see also the first article above) that breeding, towards the highly specialized structure of a commercial dent corn has eliminated many characters essential for in vitro responses at the cell level.
H. S. Dhaliwal and H. Lorz
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