Adventitious embryogenesis and plantlet regeneration from ovules of unpollinated ovaries of papaya (Carica papaya L.)

Ovules were excised from unpollinated papaya ovaries before flowering and imbedded on the culture media containing cytokinin, auxin, and gibberellins. Adventitious embryos were induced only in the culture media with mixed gibberellins and GA3 in the dark. No embryo was initiated with cytokinin and auxin, whereas the gibberellin mixture(GA(3)>80%, GA(1)+GA(4) is approximately equal to 10%, minute amount of GA(2)+GA(7)), GA(3), and GA(4) individually promoted induction, but GA(1), GA(5), and GA(7) were ineffective. The adventitious embryos were directly induced from the ovules. However, there were many abnormal embryos with malformed cotyledons. The induced embryos were transferred onto a hormone -free MS medium to regenerate plantlets. Plantlets, derived from embryos with gibberellin mixture, GA3, and GA4, and their respective percentages were 18.6, 26.4, and 26.9. The total number of surviving plants after acclimatization was only 44 (7.2%). All acclimated plants were diploid (2n=18), whereas some of the adventitious embryos were heteroploid and tetraploid (4n=36). RAPD analyses of the regenerated plants using primer RA-1 and RA-47 showed that several had differing banding patterns from those of their parents. Therefore, it is suggested that some of the regenerated plants were induced from haploidic reproductive cells.