In tissue culture, use of various plant growth regulators has been sho
wn to modify callus growth and plant regeneration rates. This study ex
amined the effects of 0.5, 1.0, 1.5 and 2.0 mu M concentrations and tw
o modes of application of abscisic acid (ABA), namely in the medium an
d topical application, on callus growth and plant regeneration of two
wheat (Triticum aestivum L.) genotypes, PI 137739 and 'Stephens'. Call
us induction and proliferation were arrested by ABA treatments in the
first month. Enhanced growth of up to 3-fold was observed in ABA treat
ed calli compared to control when they were transferred to maintenance
medium without ABA in the second month. In 'Stephens', increased plan
tlet production was observed when ABA was incorporated in the medium.
Thus, wheat genotypes responded differently to ABA treatments with reg
ards to calli growth and plant regeneration capability.