Somatic embryogenesis was improved in guava (Psidium guajava L.) cv. Allahabad safeda by periodic subculture of zygotic embryos explants (10-weeks post-anthesis) onto 3% (w/v) sucrose containing plant growth regulator free full-strength Murashige and Skoog’s agar-solidified medium following an initial induction in the presence of 2,4-dichlorophenoxy acetic acid (2,4-D). The interaction of 2,4-D concentrations and treatment durations showed significant effects on six different embryogenesis parameters viz. (i) frequency of embryogenesis, (ii) intensity of embryogenesis, (iii) frequency of elongated torpedo-stage somatic embryos, (iv) frequency of short torpedo-stage somatic embryos, (v) frequency of lower- (cotyledonary, heart, and globular) stages somatic embryos, and (vi) efficiency of embryogenesis. The embryogenesis responses were shifted gradually from 0.01 mgl^-1 to 0.5 mgl^-1 concentrations 2,4-D in a temporal manner. An 8-days treatment of zygotic embryo explants with 0.5 mgl^-1 2,4-D induced somatic embryogenesis in highest efficiency. The role of exogenous and endogenous concentration of total, free, conjugated, and bound forms of various polyamines viz. putrescine, spermidine and spermine were studied and discussed in regulation of somatic embryogenesis as a function of 2,4-D concentration. The present study on guava (P. guajava L.) cv. safeda indicated that temporal regulation of somatic embryogenesis by 2,4-D was modulated by polyamines metabolism.

guava, polyamines, somatic embryogenesis, zygotic embryo