In Vitro Long-Term Cultures of Papaya (Carica Papaya L.).

Abstract We present the data on proliferation corresponding to 10 years of continuous incubation in vitro of papaya shoots, and propose a reliable method for long-term micropropagation for papaya, using two types of explants: Microshoots from somatic embryos, and from axillary buds of papaya. Three different media were assayed. The proliferation medium (PPRM) allowed to maintain papaya shoots under continuous proliferation during 20 years, maintaining a consistent behaviour. Most of the shoots developed in PPRM rooted during the incubation, and after acclimated easily, maintaining the morphological characteristics of the parental plants, flowering and setting fruits normally. The PPRM medium consist in MS medium supplemented with NAA (0.1 mg l-1), BA (0.5 mg l-1), GA3 (0.5 mg l-1) and Adenine sulphate (40 mg l-1). The average multiplication rate was higher than 20 shoots per explant along the long-term assay. The elongation medium (PELM), was designed to recover shoots with a poor growth, and allowed the development of high quality shoots ready for rooting, and consist in a MS basal medium supplemented with NAA (0.1 mg l-1), Kin (0.5 mg l-1) and GA3 (1 mg l-1). The rooting medium (PROM) was designed to induce high quality roots from non-rooted shoots and consist in a half strength MS medium plus IBA (1mg l-1). On PROM, agar can be exchanged for expanded vermiculite. Acclimation took place inside an acclimatization tunnel under progressive hydric stress. After 4 weeks, the plant recovery rate was 90% for plants maintained under continuous proliferation during ten years.