Unlike rice embryogenic callus which can maintain regenerability
over 40 weeks (Nabors et al., 1983), sorghum embryogenic callus does
not maintain a useful level of regenerability over four weeks. The reason
for this phenomenon is, as yet, unknown. Our data from three tested
lines unequivocally demonstrated that the optimal callus age was
two-weeks old. When callus was four-weeks old, the regeneration
rate and regenerability dropped markedly. For instance, SA281 could
produce 59 shoots per IE when callus was two-weeks old; however, it
only generated 3 shoots per IE when callus was four-weeks old
(Table 4). Therefore, callus age plays a critical role on regenerability