RECURRENT SELECTION FOR REGENERATION CAPACITY FROM IMMATURE EMBRYO-DERIVED CALLI IN MAIZE

Two cycles of recurrent selection to improve regeneration capacity fro m immature embryo-derived calli were implemented in the maize (Zea may s L.) double cross [(A188 x W64A) x (A634 x B79)]. The total number of shoots regenerated per embryo (TNSE) in two consecutive subcultures w as the selection criterion. After two cycles of selection, TNSE increa sed from 0.82 to 1.50 (+83%). A significant but lower increase (from 3 7.5-46.3%) was also noticed for the percentage of callus surface with embryo-like structures (PCE) at 4 wk after explanting, while no respon se was observed for callus fresh weight (CFW). These results indicate that recurrent selection can be successfully utilized in maize to impr ove regeneration capacity and, indirectly, the proliferation of embryo genic callus. The selection process did not lead to a decline in varia bility among progenies of the selected populations for TNSE, CFW, and PCE, suggesting that these traits are controlled by polygenic systems. For TNSE the mean value of parental lines was very close to the mean value of the A188 x W64A and A634 x B79 F2 generations and to the mean value of the source populations, indicating that the trait is mainly controlled by additive gene action. The limited indirect response to s election observed for PCE and CFW as well as low correlations of PCE a nd CFW with the trait under selection (TNSE) indicate that different s ets of genes are likely involved in controlling expression of PCE and CFW.