Massal Induction of Carica papaya L. ^|^lsquo;Golden^|^rsquo; Somatic Embryos and Somaclone Screening by Flow Cytometry and Cytogenetic Analysis

Abstract

Summary Somatic embryogenesis is a relevant micropropagation technique in Carica papaya �Goldenin 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.