Massal Induction of Carica papaya L. 'Golden' Somatic Embryos and Somaclone Screening by Flow Cytometry and Cytogenetic Analysis

Somatic embryogenesis is a relevant micropropagation technique in Carica papaya 'Golden' in view of the difficulties met in conventional seed propagation and the lack of an effective method for early sex determination in this trioecious species. Considering the interest in large-scale production of C. papaya seedlings, we adapted a somatic embryogenesis procedure associating liquid system and immature zygotic embryo explants. This protocol markedly contributed to an increase in the yield of friable embryogenic calli, resulting in a large number of normal somatic embryos at various developmental stages. From these embryos, plantlets were regenerated and evaluated for occurrence of somaclonal variation. Flow cytometry screening revealed diploid (88%), tetraploid (6%), and aneuploid (6%) plantlets. Owing to an interest in the mass propagation of diploid individuals, the karyotype of these plantlets was also analyzed. With this approach, diploidy (2X-18) was confirmed and no structural aberrations were found. Considering the results and the applicability of large-scale production of somatic embryos in C. papaya, the tissue culture protocols shown here could be used for commercial purposes. Moreover, the cytometric and cytogenetic analyses were crucial for a rapid, reliable and conclusive evaluation of the genetic stability of C. papaya plantlets regenerated by somatic embryogenesis.