Somatic embryogenesis, regeneration, phenotypic and cytological evaluation of selected Philippine papaya (Carica papaya L.) genotypes
2019
Magdalita, P.M. | San Pascual, A.O.
The use of artificial seeds using somatic embryos induced from zygotic embryos of papaya was explored as a way of rapidly increasing plant production in vitro. Cross- and self-pollination of selected parents and inbred lines, respectively, was done to generate zygotic embryos as explants materials. These genetic materials contain tolerance to Papaya ringspot virus type-P (PRSV-P). Ninety to 120 d-old papaya fruit of selected inbred lines and hybrids were harvested and ivory-colored seeds were dissected to obtain the zygotic embryos. These embryos were explanted in MS medium supplemented with 10 mg L-1 2,4-D. A mixture of somatic embryos and calli developed on the apical dome of the zygotic embryos 1-2 months after explanting and continue to proliferate until the 6th month after explanting. Torpedo-type somatic embryos mixed with calli developed 8 months after explanting on De Fossard medium without plant growth regulators. These embryos regenerated into whole plants with complete roots and shoot 7-8 months after explanting. They were acclimatized inside an acclimatization box placed inside the screenhouse and hardened seedlings were planted in the field and evaluated for phenotypic characteristics. Tree and fruit characteristics of the somatic embryo-derived plants are similar to the seed-derived control plants. Inbred line 4172 produced 8 sexually ambivalent male (SAM) plants out of 34 (23.5%) regenerants from somatic embryogenesis, which may indicate the occurrence of somaclonal variation. The SAM exhibited chromosomal aberrations such as laggards, bridges, univalent and unpaired chromosomes during metaphase of meiotic cells. However, these laggards catch up and were able to migrate to the opposite poles during telophase. The abnormal meiotic cells later reverted to normal leading to high pollen viability and germination.
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