BATON ROUGE, LOUISIANA

Louisiana State University Agricultural Center

DEBRECEN, HUNGARY

University of Agricultural Sciences

Somatic embryogenesis in S0, S1, and S2 generations of two maize populations

--Paul Pepo, Manjit S. Kang, Neeraja Kondapi and J. Ivan Dickson

Two maize populations developed in the LSU maize breeding program, viz., [(Mo17 x B73) x (L91R x Yellow Creole)] and [(Mo17 x B73) x (L331 x Yellow Creole)], hereafter referred to as L91R population and L331 population, respectively, were evaluated for their in vitro culturability and regeneration potential. The S0, S1, and S2 generations were subjected to tissue culture using the following procedures:

Seeds were surface-sterilized for 10 min. in a 0.2% aqueous mercurous chloride solution, rinsed overnight under running tap water, and re-sterilized for 5 min. in a 0.2% aqueous mercurous chloride solution, followed by several water rinses. Twenty five kernels of each generation were germinated. Aseptic seedlings were grown on a 1% agar-solidified medium containing the inorganic constituents of Murashige and Skoog (Physiol. Plant. 42:139-145, 1962), 3% sucrose, 26.7µM glycine, 4.1µM nicotinic acid, 2.4µM pyridoxine-HCl and 0.3µM thiamine-HCl.

Radicles were aseptically separated from plumules at scutellar nodes and the explants were cut into five, 2-3mm long pieces. These explants and intact, mature embryos were plated on MS medium. The pH was adjusted to 5.8 before autoclaving. Incubation was done at 26 C with 16/8 photoperiod.

The 2,4-D concentration varied between 1 and 5mg/L. After callus induction, meristematic segments were discarded; the remainder were transferred to the above culture medium for callus proliferation. To induce further differentiation, calli were subcultured on MS medium supplemented with different concentrations of 2,4-D and zeatin. Regenerated plantlets were transferred to hormone-free medium for root development.

Results (Table 1) indicated that the callus induction frequency for the two populations ranged from 4.7 to 60.9%. The highest

Table 1. Callus initiation and regeneration for L331 and L91R populations
 
   
Callus induction (%)
Regeneration (%)
Explant Inbred stage L331  L91R L331 L91R
Radicle (R) S0 60.9 41.1 4.75 1.51
  S1 58.0 32.0 4.45 0.0
  S2 56.0 23.9 0.0 0.0
  Mean 58.3 33.4 2.70 0.59
Plumule (P) S0 41.9 30.1 9.94 3.05
  S1 39.0 23.9 6.65 1.26
  S2 38.9 19.0 4.43 0.0
  Mean 40.0 25.1 6.95 1.65
Embryo (E) S0 40.0 9.8 5.00 2.17
  S1 38.2 7.2 2.06 1.20
  S2 35.8 4.7 1.05 0.0
  Mean 38.0 7.5 2.75 1.25
Mean: R+P+E S0 50.9  33.3 7.03 2.26
    (601/1181) (228/1016) (83/1181) (23/1016)
  S1 47.9 26.1 4.79 0.67
    (590/1232) (233/893) (59/1232) (6/893)
  S2 46.9 19.9 3.92 0.0
    (577/1230) (134/673) (25/1230) (0/673)

frequency of callus formation was exhibited by the radicle tissue and the lowest by the embryo. In both populations, callus induction frequency decreased as amount of homozygosity increased, which suggested that callus induction was controlled primarily by dominant gene action.

Explants differed in plant regeneration percentages in both populations. A maximum number of plants was regenerated from plumule in the L331 population. No plant regeneration was noted in the S2 generation of L91R population. Results suggested that plant regeneration would be increasingly more difficult in the inbred generations and that prior to embarking on a tissue culture-based breeding program, responsive genotypes must be identified for use in a breeding program.


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