The androgenic callus induction and plant regeneration with the least response through anther culture are the key problems in biotechnology-based papaya (Carica papaya L.) breeding. Improvement of papaya response by anther culture through flower size and PGRs’ combinations earnestly need investigation. The presented research aimed to determine the microspore stage and viability based on the flower size and a combination of plant growth regulators (PGRs) in MS (Murashige and Skoog) medium to induce embryogenic callus and somatic embryos in papaya. Explants used in the study were the anthers of hermaphrodite flowers. This study comprised three different experiments, i.e., microspore development and viability test, 2,4-D (2,4-Dichlorophenoxyacetic acid) and TDZ (Thidiazuron) optimization for embryogenic callus induction, and NAA (naphthalene acetic acid) and CPPU (N-[2-Chloro-4-pyridyl]-N’-phenylurea) optimization for somatic embryos’ formation. Results revealed hermaphrodite flower buds were 10–25 mm in length, which can be effective for embryogenic callus induction as they contained the high percentage of uninucleate stage microspores and demonstrated high viability (>95%). The combination treatment of 2,4-D (0.1 mg L^-1) and TDZ (0.5 mg L^-1) induced the most percentage of anther forming callus (20.4%), with 58.7% of that as embryogenic callus. The combination of NAA (0.1 mg L^-1) and CPPU (0.5 mg L^-1) resulted in 70% embryogenic callus plated developed into the maximum average globular embryos (38.8).

Keywords: Papaya (C. papaya L.), callus induction, flower size, hermaphrodite flowers, microspores stage, 2,4-D, TDZ, NAA, CPPU

Key findings: The induction of somatic embryos in papaya (C. papaya L.) anther culture can be successful through an appropriate size of hermaphrodite flowers and the use of PGRs’ combination in the culture medium. This information is crucial to support papaya breeding programs to obtain double haploid lines through anther culture.